X-Git-Url: https://wimlib.net/git/?p=wimlib;a=blobdiff_plain;f=src%2Flzms-compress.c;h=da1904fc9f66cf8927db8a08cc31176a7e9c4c51;hp=871c12c7aac817e6ea1cecd29e7e7ea733b7ace9;hb=a5f0f107247cc6400c0bd25f41e49d658fd2b7d7;hpb=91b0f909393476f39ed5865dfe4b27c244ba3c48

diff --git a/src/lzms-compress.c b/src/lzms-compress.c
index 871c12c7..da1904fc 100644
--- a/src/lzms-compress.c
+++ b/src/lzms-compress.c
@@ -1,47 +1,36 @@
 /*
  * lzms-compress.c
+ *
+ * A compressor that produces output compatible with the LZMS compression format.
  */
 
 /*
  * Copyright (C) 2013, 2014 Eric Biggers
  *
- * This file is part of wimlib, a library for working with WIM files.
- *
- * wimlib is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free
- * Software Foundation; either version 3 of the License, or (at your option)
- * any later version.
+ * This file is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation; either version 3 of the License, or (at your option) any
+ * later version.
  *
- * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * This file is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
  * details.
  *
- * You should have received a copy of the GNU General Public License
- * along with wimlib; if not, see http://www.gnu.org/licenses/.
- */
-
-/* This a compressor for the LZMS compression format.  More details about this
- * format can be found in lzms-decompress.c.
- *
- * Also see lzx-compress.c for general information about match-finding and
- * match-choosing that also applies to this LZMS compressor.
- *
- * NOTE: this compressor currently does not code any delta matches.
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this file; if not, see http://www.gnu.org/licenses/.
  */
 
 #ifdef HAVE_CONFIG_H
 #  include "config.h"
 #endif
 
-#include "wimlib.h"
-#include "wimlib/assert.h"
-#include "wimlib/compiler.h"
-#include "wimlib/compressor_ops.h"
 #include "wimlib/compress_common.h"
+#include "wimlib/compressor_ops.h"
 #include "wimlib/endianness.h"
 #include "wimlib/error.h"
 #include "wimlib/lz_mf.h"
+#include "wimlib/lz_repsearch.h"
 #include "wimlib/lzms.h"
 #include "wimlib/util.h"
 
@@ -49,31 +38,28 @@
 #include <limits.h>
 #include <pthread.h>
 
-/* Stucture used for writing raw bits to the end of the LZMS-compressed data as
- * a series of 16-bit little endian coding units.  */
+/* Stucture used for writing raw bits as a series of 16-bit little endian coding
+ * units.  This starts at the *end* of the compressed data buffer and proceeds
+ * backwards.  */
 struct lzms_output_bitstream {
-	/* Buffer variable containing zero or more bits that have been logically
-	 * written to the bitstream but not yet written to memory.  This must be
-	 * at least as large as the coding unit size.  */
-	u16 bitbuf;
 
-	/* Number of bits in @bitbuf that are valid.  */
-	unsigned num_free_bits;
+	/* Bits that haven't yet been written to the output buffer.  */
+	u64 bitbuf;
+
+	/* Number of bits currently held in @bitbuf.  */
+	unsigned bitcount;
 
 	/* Pointer to one past the next position in the compressed data buffer
 	 * at which to output a 16-bit coding unit.  */
-	le16 *out;
-
-	/* Maximum number of 16-bit coding units that can still be output to
-	 * the compressed data buffer.  */
-	size_t num_le16_remaining;
+	le16 *next;
 
-	/* Set to %true if not all coding units could be output due to
-	 * insufficient space.  */
-	bool overrun;
+	/* Pointer to the beginning of the output buffer.  (The "end" when
+	 * writing backwards!)  */
+	le16 *begin;
 };
 
-/* Stucture used for range encoding (raw version).  */
+/* Stucture used for range encoding (raw version).  This starts at the
+ * *beginning* of the compressed data buffer and proceeds forward.  */
 struct lzms_range_encoder_raw {
 
 	/* A 33-bit variable that holds the low boundary of the current range.
@@ -91,25 +77,21 @@ struct lzms_range_encoder_raw {
 	 * subsequent such coding units are 0xffff.  */
 	u32 cache_size;
 
-	/* Pointer to the next position in the compressed data buffer at which
-	 * to output a 16-bit coding unit.  */
-	le16 *out;
+	/* Pointer to the beginning of the output buffer.  */
+	le16 *begin;
 
-	/* Maximum number of 16-bit coding units that can still be output to
-	 * the compressed data buffer.  */
-	size_t num_le16_remaining;
+	/* Pointer to the position in the output buffer at which the next coding
+	 * unit must be written.  */
+	le16 *next;
 
-	/* %true when the very first coding unit has not yet been output.  */
-	bool first;
-
-	/* Set to %true if not all coding units could be output due to
-	 * insufficient space.  */
-	bool overrun;
+	/* Pointer just past the end of the output buffer.  */
+	le16 *end;
 };
 
 /* Structure used for range encoding.  This wraps around `struct
  * lzms_range_encoder_raw' to use and maintain probability entries.  */
 struct lzms_range_encoder {
+
 	/* Pointer to the raw range encoder, which has no persistent knowledge
 	 * of probabilities.  Multiple lzms_range_encoder's share the same
 	 * lzms_range_encoder_raw.  */
@@ -157,6 +139,7 @@ struct lzms_huffman_encoder {
 	u32 codewords[LZMS_MAX_NUM_SYMS];
 };
 
+/* Internal compression parameters  */
 struct lzms_compressor_params {
 	u32 min_match_length;
 	u32 nice_match_length;
@@ -164,44 +147,35 @@ struct lzms_compressor_params {
 	u32 optim_array_length;
 };
 
-/* State of the LZMS compressor.  */
+/* State of the LZMS compressor  */
 struct lzms_compressor {
-	/* Pointer to a buffer holding the preprocessed data to compress.  */
-	u8 *window;
 
-	/* Current position in @buffer.  */
-	u32 cur_window_pos;
+	/* Internal compression parameters  */
+	struct lzms_compressor_params params;
 
-	/* Size of the data in @buffer.  */
-	u32 window_size;
+	/* Data currently being compressed  */
+	u8 *cur_window;
+	u32 cur_window_size;
 
-	/* Lempel-Ziv match-finder.  */
+	/* Lempel-Ziv match-finder  */
 	struct lz_mf *mf;
 
-	/* Temporary space to store found matches.  */
+	/* Temporary space to store found matches  */
 	struct lz_match *matches;
 
-	/* Match-chooser data.  */
+	/* Per-position data for near-optimal parsing  */
 	struct lzms_mc_pos_data *optimum;
-	unsigned optimum_cur_idx;
-	unsigned optimum_end_idx;
-
-	/* Maximum block size this compressor instantiation allows.  This is the
-	 * allocated size of @window.  */
-	u32 max_block_size;
-
-	/* Compression parameters.  */
-	struct lzms_compressor_params params;
+	struct lzms_mc_pos_data *optimum_end;
 
 	/* Raw range encoder which outputs to the beginning of the compressed
-	 * data buffer, proceeding forwards.  */
+	 * data buffer, proceeding forwards  */
 	struct lzms_range_encoder_raw rc;
 
 	/* Bitstream which outputs to the end of the compressed data buffer,
-	 * proceeding backwards.  */
+	 * proceeding backwards  */
 	struct lzms_output_bitstream os;
 
-	/* Range encoders.  */
+	/* Range encoders  */
 	struct lzms_range_encoder main_range_encoder;
 	struct lzms_range_encoder match_range_encoder;
 	struct lzms_range_encoder lz_match_range_encoder;
@@ -209,33 +183,79 @@ struct lzms_compressor {
 	struct lzms_range_encoder delta_match_range_encoder;
 	struct lzms_range_encoder delta_repeat_match_range_encoders[LZMS_NUM_RECENT_OFFSETS - 1];
 
-	/* Huffman encoders.  */
+	/* Huffman encoders  */
 	struct lzms_huffman_encoder literal_encoder;
 	struct lzms_huffman_encoder lz_offset_encoder;
 	struct lzms_huffman_encoder length_encoder;
 	struct lzms_huffman_encoder delta_power_encoder;
 	struct lzms_huffman_encoder delta_offset_encoder;
 
-	/* LRU (least-recently-used) queues for match information.  */
-	struct lzms_lru_queues lru;
-
-	/* Used for preprocessing.  */
+	/* Used for preprocessing  */
 	s32 last_target_usages[65536];
+
+#define LZMS_NUM_FAST_LENGTHS 256
+	/* Table: length => length slot for small lengths  */
+	u8 length_slot_fast[LZMS_NUM_FAST_LENGTHS];
+
+	/* Table: length => current cost for small match lengths  */
+	u32 length_cost_fast[LZMS_NUM_FAST_LENGTHS];
+
+#define LZMS_NUM_FAST_OFFSETS 32768
+	/* Table: offset => offset slot for small offsets  */
+	u8 offset_slot_fast[LZMS_NUM_FAST_OFFSETS];
 };
 
+/*
+ * Match chooser position data:
+ *
+ * An array of these structures is used during the near-optimal match-choosing
+ * algorithm.  They correspond to consecutive positions in the window and are
+ * used to keep track of the cost to reach each position, and the match/literal
+ * choices that need to be chosen to reach that position.
+ */
 struct lzms_mc_pos_data {
+
+	/* The cost, in bits, of the lowest-cost path that has been found to
+	 * reach this position.  This can change as progressively lower cost
+	 * paths are found to reach this position.  */
 	u32 cost;
-#define MC_INFINITE_COST ((u32)~0UL)
-	union {
-		struct {
-			u32 link;
-			u32 match_offset;
-		} prev;
-		struct {
-			u32 link;
-			u32 match_offset;
-		} next;
-	};
+#define MC_INFINITE_COST UINT32_MAX
+
+	/* The match or literal that was taken to reach this position.  This can
+	 * change as progressively lower cost paths are found to reach this
+	 * position.
+	 *
+	 * This variable is divided into two bitfields.
+	 *
+	 * Literals:
+	 *	Low bits are 1, high bits are the literal.
+	 *
+	 * Explicit offset matches:
+	 *	Low bits are the match length, high bits are the offset plus 2.
+	 *
+	 * Repeat offset matches:
+	 *	Low bits are the match length, high bits are the queue index.
+	 */
+	u64 mc_item_data;
+#define MC_OFFSET_SHIFT 32
+#define MC_LEN_MASK (((u64)1 << MC_OFFSET_SHIFT) - 1)
+
+	/* The LZMS adaptive state that exists at this position.  This is filled
+	 * in lazily, only after the minimum-cost path to this position is
+	 * found.
+	 *
+	 * Note: the way we handle this adaptive state in the "minimum-cost"
+	 * parse is actually only an approximation.  It's possible for the
+	 * globally optimal, minimum cost path to contain a prefix, ending at a
+	 * position, where that path prefix is *not* the minimum cost path to
+	 * that position.  This can happen if such a path prefix results in a
+	 * different adaptive state which results in lower costs later.  We do
+	 * not solve this problem; we only consider the lowest cost to reach
+	 * each position, which seems to be an acceptable approximation.
+	 *
+	 * Note: this adaptive state also does not include the probability
+	 * entries or current Huffman codewords.  Those aren't maintained
+	 * per-position and are only updated occassionally.  */
 	struct lzms_adaptive_state {
 		struct lzms_lz_lru_queues lru;
 		u8 main_state;
@@ -245,60 +265,101 @@ struct lzms_mc_pos_data {
 	} state;
 };
 
-/* Initialize the output bitstream @os to write forwards to the specified
+static void
+lzms_init_fast_slots(struct lzms_compressor *c)
+{
+	/* Create table mapping small lengths to length slots.  */
+	for (unsigned slot = 0, i = 0; i < LZMS_NUM_FAST_LENGTHS; i++) {
+		while (i >= lzms_length_slot_base[slot + 1])
+			slot++;
+		c->length_slot_fast[i] = slot;
+	}
+
+	/* Create table mapping small offsets to offset slots.  */
+	for (unsigned slot = 0, i = 0; i < LZMS_NUM_FAST_OFFSETS; i++) {
+		while (i >= lzms_offset_slot_base[slot + 1])
+			slot++;
+		c->offset_slot_fast[i] = slot;
+	}
+}
+
+static inline unsigned
+lzms_get_length_slot_fast(const struct lzms_compressor *c, u32 length)
+{
+	if (likely(length < LZMS_NUM_FAST_LENGTHS))
+		return c->length_slot_fast[length];
+	else
+		return lzms_get_length_slot(length);
+}
+
+static inline unsigned
+lzms_get_offset_slot_fast(const struct lzms_compressor *c, u32 offset)
+{
+	if (offset < LZMS_NUM_FAST_OFFSETS)
+		return c->offset_slot_fast[offset];
+	else
+		return lzms_get_offset_slot(offset);
+}
+
+/* Initialize the output bitstream @os to write backwards to the specified
  * compressed data buffer @out that is @out_limit 16-bit integers long.  */
 static void
 lzms_output_bitstream_init(struct lzms_output_bitstream *os,
 			   le16 *out, size_t out_limit)
 {
 	os->bitbuf = 0;
-	os->num_free_bits = 16;
-	os->out = out + out_limit;
-	os->num_le16_remaining = out_limit;
-	os->overrun = false;
+	os->bitcount = 0;
+	os->next = out + out_limit;
+	os->begin = out;
 }
 
-/* Write @num_bits bits, contained in the low @num_bits bits of @bits (ordered
- * from high-order to low-order), to the output bitstream @os.  */
-static void
-lzms_output_bitstream_put_bits(struct lzms_output_bitstream *os,
-			       u32 bits, unsigned num_bits)
+/*
+ * Write some bits, contained in the low @num_bits bits of @bits (ordered from
+ * high-order to low-order), to the output bitstream @os.
+ *
+ * @max_num_bits is a compile-time constant that specifies the maximum number of
+ * bits that can ever be written at this call site.
+ */
+static inline void
+lzms_output_bitstream_put_varbits(struct lzms_output_bitstream *os,
+				  u32 bits, unsigned num_bits,
+				  unsigned max_num_bits)
 {
-	bits &= (1U << num_bits) - 1;
+	LZMS_ASSERT(num_bits <= 48);
 
-	while (num_bits > os->num_free_bits) {
+	/* Add the bits to the bit buffer variable.  */
+	os->bitcount += num_bits;
+	os->bitbuf = (os->bitbuf << num_bits) | bits;
 
-		if (unlikely(os->num_le16_remaining == 0)) {
-			os->overrun = true;
-			return;
-		}
+	/* Check whether any coding units need to be written.  */
+	while (os->bitcount >= 16) {
 
-		unsigned num_fill_bits = os->num_free_bits;
+		os->bitcount -= 16;
 
-		os->bitbuf <<= num_fill_bits;
-		os->bitbuf |= bits >> (num_bits - num_fill_bits);
+		/* Write a coding unit, unless it would underflow the buffer. */
+		if (os->next != os->begin)
+			*--os->next = cpu_to_le16(os->bitbuf >> os->bitcount);
 
-		*--os->out = cpu_to_le16(os->bitbuf);
-		--os->num_le16_remaining;
-
-		os->num_free_bits = 16;
-		num_bits -= num_fill_bits;
-		bits &= (1U << num_bits) - 1;
+		/* Optimization for call sites that never write more than 16
+		 * bits at once.  */
+		if (max_num_bits <= 16)
+			break;
 	}
-	os->bitbuf <<= num_bits;
-	os->bitbuf |= bits;
-	os->num_free_bits -= num_bits;
 }
 
 /* Flush the output bitstream, ensuring that all bits written to it have been
- * written to memory.  Returns %true if all bits were output successfully, or
- * %false if an overrun occurred.  */
+ * written to memory.  Returns %true if all bits have been output successfully,
+ * or %false if an overrun occurred.  */
 static bool
 lzms_output_bitstream_flush(struct lzms_output_bitstream *os)
 {
-	if (os->num_free_bits != 16)
-		lzms_output_bitstream_put_bits(os, 0, os->num_free_bits + 1);
-	return !os->overrun;
+	if (os->next == os->begin)
+		return false;
+
+	if (os->bitcount != 0)
+		*--os->next = cpu_to_le16(os->bitbuf << (16 - os->bitcount));
+
+	return true;
 }
 
 /* Initialize the range encoder @rc to write forwards to the specified
@@ -311,10 +372,9 @@ lzms_range_encoder_raw_init(struct lzms_range_encoder_raw *rc,
 	rc->range = 0xffffffff;
 	rc->cache = 0;
 	rc->cache_size = 1;
-	rc->out = out;
-	rc->num_le16_remaining = out_limit;
-	rc->first = true;
-	rc->overrun = false;
+	rc->begin = out;
+	rc->next = out - 1;
+	rc->end = out + out_limit;
 }
 
 /*
@@ -334,26 +394,19 @@ lzms_range_encoder_raw_init(struct lzms_range_encoder_raw *rc,
 static void
 lzms_range_encoder_raw_shift_low(struct lzms_range_encoder_raw *rc)
 {
-	LZMS_DEBUG("low=%"PRIx64", cache=%"PRIx64", cache_size=%u",
-		   rc->low, rc->cache, rc->cache_size);
 	if ((u32)(rc->low) < 0xffff0000 ||
 	    (u32)(rc->low >> 32) != 0)
 	{
 		/* Carry not needed (rc->low < 0xffff0000), or carry occurred
 		 * ((rc->low >> 32) != 0, a.k.a. the carry bit is 1).  */
 		do {
-			if (!rc->first) {
-				if (rc->num_le16_remaining == 0) {
-					rc->overrun = true;
-					return;
-				}
-				*rc->out++ = cpu_to_le16(rc->cache +
-							 (u16)(rc->low >> 32));
-				--rc->num_le16_remaining;
+			if (likely(rc->next >= rc->begin)) {
+				if (rc->next != rc->end)
+					*rc->next++ = cpu_to_le16(rc->cache +
+								  (u16)(rc->low >> 32));
 			} else {
-				rc->first = false;
+				rc->next++;
 			}
-
 			rc->cache = 0xffff;
 		} while (--rc->cache_size != 0);
 
@@ -377,15 +430,15 @@ lzms_range_encoder_raw_flush(struct lzms_range_encoder_raw *rc)
 {
 	for (unsigned i = 0; i < 4; i++)
 		lzms_range_encoder_raw_shift_low(rc);
-	return !rc->overrun;
+	return rc->next != rc->end;
 }
 
 /* Encode the next bit using the range encoder (raw version).
  *
  * @prob is the chance out of LZMS_PROBABILITY_MAX that the next bit is 0.  */
-static void
-lzms_range_encoder_raw_encode_bit(struct lzms_range_encoder_raw *rc, int bit,
-				  u32 prob)
+static inline void
+lzms_range_encoder_raw_encode_bit(struct lzms_range_encoder_raw *rc,
+				  int bit, u32 prob)
 {
 	lzms_range_encoder_raw_normalize(rc);
 
@@ -400,7 +453,7 @@ lzms_range_encoder_raw_encode_bit(struct lzms_range_encoder_raw *rc, int bit,
 
 /* Encode a bit using the specified range encoder. This wraps around
  * lzms_range_encoder_raw_encode_bit() to handle using and updating the
- * appropriate probability table.  */
+ * appropriate state and probability entry.  */
 static void
 lzms_range_encode_bit(struct lzms_range_encoder *enc, int bit)
 {
@@ -410,207 +463,197 @@ lzms_range_encode_bit(struct lzms_range_encoder *enc, int bit)
 	/* Load the probability entry corresponding to the current state.  */
 	prob_entry = &enc->prob_entries[enc->state];
 
-	/* Treat the number of zero bits in the most recently encoded
-	 * LZMS_PROBABILITY_MAX bits with this probability entry as the chance,
-	 * out of LZMS_PROBABILITY_MAX, that the next bit will be a 0.  However,
-	 * don't allow 0% or 100% probabilities.  */
-	prob = prob_entry->num_recent_zero_bits;
-	if (prob == 0)
-		prob = 1;
-	else if (prob == LZMS_PROBABILITY_MAX)
-		prob = LZMS_PROBABILITY_MAX - 1;
-
-	/* Encode the next bit.  */
+	/* Update the state based on the next bit.  */
+	enc->state = ((enc->state << 1) | bit) & enc->mask;
+
+	/* Get the probability that the bit is 0.  */
+	prob = lzms_get_probability(prob_entry);
+
+	/* Update the probability entry.  */
+	lzms_update_probability_entry(prob_entry, bit);
+
+	/* Encode the bit.  */
 	lzms_range_encoder_raw_encode_bit(enc->rc, bit, prob);
+}
 
-	/* Update the state based on the newly encoded bit.  */
-	enc->state = ((enc->state << 1) | bit) & enc->mask;
+/* Called when an adaptive Huffman code needs to be rebuilt.  */
+static void
+lzms_rebuild_huffman_code(struct lzms_huffman_encoder *enc)
+{
+	make_canonical_huffman_code(enc->num_syms,
+				    LZMS_MAX_CODEWORD_LEN,
+				    enc->sym_freqs,
+				    enc->lens,
+				    enc->codewords);
 
-	/* Update the recent bits, including the cached count of 0's.  */
-	BUILD_BUG_ON(LZMS_PROBABILITY_MAX > sizeof(prob_entry->recent_bits) * 8);
-	if (bit == 0) {
-		if (prob_entry->recent_bits & (1ULL << (LZMS_PROBABILITY_MAX - 1))) {
-			/* Replacing 1 bit with 0 bit; increment the zero count.
-			 */
-			prob_entry->num_recent_zero_bits++;
-		}
-	} else {
-		if (!(prob_entry->recent_bits & (1ULL << (LZMS_PROBABILITY_MAX - 1)))) {
-			/* Replacing 0 bit with 1 bit; decrement the zero count.
-			 */
-			prob_entry->num_recent_zero_bits--;
-		}
+	/* Dilute the frequencies.  */
+	for (unsigned i = 0; i < enc->num_syms; i++) {
+		enc->sym_freqs[i] >>= 1;
+		enc->sym_freqs[i] += 1;
 	}
-	prob_entry->recent_bits = (prob_entry->recent_bits << 1) | bit;
+	enc->num_syms_written = 0;
 }
 
 /* Encode a symbol using the specified Huffman encoder.  */
-static void
-lzms_huffman_encode_symbol(struct lzms_huffman_encoder *enc, u32 sym)
+static inline void
+lzms_huffman_encode_symbol(struct lzms_huffman_encoder *enc, unsigned sym)
 {
-	LZMS_ASSERT(sym < enc->num_syms);
-	lzms_output_bitstream_put_bits(enc->os,
-				       enc->codewords[sym],
-				       enc->lens[sym]);
+	lzms_output_bitstream_put_varbits(enc->os,
+					  enc->codewords[sym],
+					  enc->lens[sym],
+					  LZMS_MAX_CODEWORD_LEN);
 	++enc->sym_freqs[sym];
-	if (++enc->num_syms_written == enc->rebuild_freq) {
-		/* Adaptive code needs to be rebuilt.  */
-		LZMS_DEBUG("Rebuilding code (num_syms=%u)", enc->num_syms);
-		make_canonical_huffman_code(enc->num_syms,
-					    LZMS_MAX_CODEWORD_LEN,
-					    enc->sym_freqs,
-					    enc->lens,
-					    enc->codewords);
-
-		/* Dilute the frequencies.  */
-		for (unsigned i = 0; i < enc->num_syms; i++) {
-			enc->sym_freqs[i] >>= 1;
-			enc->sym_freqs[i] += 1;
-		}
-		enc->num_syms_written = 0;
-	}
+	if (++enc->num_syms_written == enc->rebuild_freq)
+		lzms_rebuild_huffman_code(enc);
 }
 
 static void
-lzms_encode_length(struct lzms_huffman_encoder *enc, u32 length)
+lzms_update_fast_length_costs(struct lzms_compressor *c);
+
+/* Encode a match length.  */
+static void
+lzms_encode_length(struct lzms_compressor *c, u32 length)
 {
 	unsigned slot;
 	unsigned num_extra_bits;
 	u32 extra_bits;
 
-	slot = lzms_get_length_slot(length);
+	slot = lzms_get_length_slot_fast(c, length);
 
+	extra_bits = length - lzms_length_slot_base[slot];
 	num_extra_bits = lzms_extra_length_bits[slot];
 
-	extra_bits = length - lzms_length_slot_base[slot];
+	lzms_huffman_encode_symbol(&c->length_encoder, slot);
+	if (c->length_encoder.num_syms_written == 0)
+		lzms_update_fast_length_costs(c);
 
-	lzms_huffman_encode_symbol(enc, slot);
-	lzms_output_bitstream_put_bits(enc->os, extra_bits, num_extra_bits);
+	lzms_output_bitstream_put_varbits(c->length_encoder.os,
+					  extra_bits, num_extra_bits, 30);
 }
 
+/* Encode an LZ match offset.  */
 static void
-lzms_encode_offset(struct lzms_huffman_encoder *enc, u32 offset)
+lzms_encode_lz_offset(struct lzms_compressor *c, u32 offset)
 {
 	unsigned slot;
 	unsigned num_extra_bits;
 	u32 extra_bits;
 
-	slot = lzms_get_position_slot(offset);
-
-	num_extra_bits = lzms_extra_position_bits[slot];
+	slot = lzms_get_offset_slot_fast(c, offset);
 
-	extra_bits = offset - lzms_position_slot_base[slot];
+	extra_bits = offset - lzms_offset_slot_base[slot];
+	num_extra_bits = lzms_extra_offset_bits[slot];
 
-	lzms_huffman_encode_symbol(enc, slot);
-	lzms_output_bitstream_put_bits(enc->os, extra_bits, num_extra_bits);
-}
-
-static void
-lzms_begin_encode_item(struct lzms_compressor *ctx)
-{
-	ctx->lru.lz.upcoming_offset = 0;
-	ctx->lru.delta.upcoming_offset = 0;
-	ctx->lru.delta.upcoming_power = 0;
-}
-
-static void
-lzms_end_encode_item(struct lzms_compressor *ctx, u32 length)
-{
-	LZMS_ASSERT(ctx->window_size - ctx->cur_window_pos >= length);
-	ctx->cur_window_pos += length;
-	lzms_update_lru_queues(&ctx->lru);
+	lzms_huffman_encode_symbol(&c->lz_offset_encoder, slot);
+	lzms_output_bitstream_put_varbits(c->lz_offset_encoder.os,
+					  extra_bits, num_extra_bits, 30);
 }
 
 /* Encode a literal byte.  */
 static void
-lzms_encode_literal(struct lzms_compressor *ctx, u8 literal)
+lzms_encode_literal(struct lzms_compressor *c, unsigned literal)
 {
-	LZMS_DEBUG("Position %u: Encoding literal 0x%02x ('%c')",
-		   ctx->cur_window_pos, literal, literal);
-
-	lzms_begin_encode_item(ctx);
-
 	/* Main bit: 0 = a literal, not a match.  */
-	lzms_range_encode_bit(&ctx->main_range_encoder, 0);
+	lzms_range_encode_bit(&c->main_range_encoder, 0);
 
 	/* Encode the literal using the current literal Huffman code.  */
-	lzms_huffman_encode_symbol(&ctx->literal_encoder, literal);
-
-	lzms_end_encode_item(ctx, 1);
+	lzms_huffman_encode_symbol(&c->literal_encoder, literal);
 }
 
-/* Encode a (length, offset) pair (LZ match).  */
+/* Encode an LZ repeat offset match.  */
 static void
-lzms_encode_lz_match(struct lzms_compressor *ctx, u32 length, u32 offset)
+lzms_encode_lz_repeat_offset_match(struct lzms_compressor *c,
+				   u32 length, unsigned rep_index)
 {
-	int recent_offset_idx;
-
-	LZMS_DEBUG("Position %u: Encoding LZ match {length=%u, offset=%u}",
-		   ctx->cur_window_pos, length, offset);
-
-	LZMS_ASSERT(length <= ctx->window_size - ctx->cur_window_pos);
-	LZMS_ASSERT(offset <= ctx->cur_window_pos);
-	LZMS_ASSERT(!memcmp(&ctx->window[ctx->cur_window_pos],
-			    &ctx->window[ctx->cur_window_pos - offset],
-			    length));
-
-	lzms_begin_encode_item(ctx);
+	unsigned i;
 
 	/* Main bit: 1 = a match, not a literal.  */
-	lzms_range_encode_bit(&ctx->main_range_encoder, 1);
+	lzms_range_encode_bit(&c->main_range_encoder, 1);
 
 	/* Match bit: 0 = an LZ match, not a delta match.  */
-	lzms_range_encode_bit(&ctx->match_range_encoder, 0);
-
-	/* Determine if the offset can be represented as a recent offset.  */
-	for (recent_offset_idx = 0;
-	     recent_offset_idx < LZMS_NUM_RECENT_OFFSETS;
-	     recent_offset_idx++)
-		if (offset == ctx->lru.lz.recent_offsets[recent_offset_idx])
-			break;
+	lzms_range_encode_bit(&c->match_range_encoder, 0);
 
-	if (recent_offset_idx == LZMS_NUM_RECENT_OFFSETS) {
-		/* Explicit offset.  */
+	/* LZ match bit: 1 = repeat offset, not an explicit offset.  */
+	lzms_range_encode_bit(&c->lz_match_range_encoder, 1);
 
-		/* LZ match bit: 0 = explicit offset, not a recent offset.  */
-		lzms_range_encode_bit(&ctx->lz_match_range_encoder, 0);
+	/* Encode the repeat offset index.  A 1 bit is encoded for each index
+	 * passed up.  This sequence of 1 bits is terminated by a 0 bit, or
+	 * automatically when (LZMS_NUM_RECENT_OFFSETS - 1) 1 bits have been
+	 * encoded.  */
+	for (i = 0; i < rep_index; i++)
+		lzms_range_encode_bit(&c->lz_repeat_match_range_encoders[i], 1);
 
-		/* Encode the match offset.  */
-		lzms_encode_offset(&ctx->lz_offset_encoder, offset);
-	} else {
-		int i;
+	if (i < LZMS_NUM_RECENT_OFFSETS - 1)
+		lzms_range_encode_bit(&c->lz_repeat_match_range_encoders[i], 0);
 
-		/* Recent offset.  */
+	/* Encode the match length.  */
+	lzms_encode_length(c, length);
+}
 
-		/* LZ match bit: 1 = recent offset, not an explicit offset.  */
-		lzms_range_encode_bit(&ctx->lz_match_range_encoder, 1);
+/* Encode an LZ explicit offset match.  */
+static void
+lzms_encode_lz_explicit_offset_match(struct lzms_compressor *c,
+				     u32 length, u32 offset)
+{
+	/* Main bit: 1 = a match, not a literal.  */
+	lzms_range_encode_bit(&c->main_range_encoder, 1);
 
-		/* Encode the recent offset index.  A 1 bit is encoded for each
-		 * index passed up.  This sequence of 1 bits is terminated by a
-		 * 0 bit, or automatically when (LZMS_NUM_RECENT_OFFSETS - 1) 1
-		 * bits have been encoded.  */
-		for (i = 0; i < recent_offset_idx; i++)
-			lzms_range_encode_bit(&ctx->lz_repeat_match_range_encoders[i], 1);
+	/* Match bit: 0 = an LZ match, not a delta match.  */
+	lzms_range_encode_bit(&c->match_range_encoder, 0);
 
-		if (i < LZMS_NUM_RECENT_OFFSETS - 1)
-			lzms_range_encode_bit(&ctx->lz_repeat_match_range_encoders[i], 0);
+	/* LZ match bit: 0 = explicit offset, not a repeat offset.  */
+	lzms_range_encode_bit(&c->lz_match_range_encoder, 0);
 
-		/* Initial update of the LZ match offset LRU queue.  */
-		for (; i < LZMS_NUM_RECENT_OFFSETS; i++)
-			ctx->lru.lz.recent_offsets[i] = ctx->lru.lz.recent_offsets[i + 1];
-	}
+	/* Encode the match offset.  */
+	lzms_encode_lz_offset(c, offset);
 
 	/* Encode the match length.  */
-	lzms_encode_length(&ctx->length_encoder, length);
+	lzms_encode_length(c, length);
+}
 
-	/* Save the match offset for later insertion at the front of the LZ
-	 * match offset LRU queue.  */
-	ctx->lru.lz.upcoming_offset = offset;
+static void
+lzms_encode_item(struct lzms_compressor *c, u64 mc_item_data)
+{
+	u32 len = mc_item_data & MC_LEN_MASK;
+	u32 offset_data = mc_item_data >> MC_OFFSET_SHIFT;
 
-	lzms_end_encode_item(ctx, length);
+	if (len == 1)
+		lzms_encode_literal(c, offset_data);
+	else if (offset_data < LZMS_NUM_RECENT_OFFSETS)
+		lzms_encode_lz_repeat_offset_match(c, len, offset_data);
+	else
+		lzms_encode_lz_explicit_offset_match(c, len, offset_data - LZMS_OFFSET_OFFSET);
 }
 
-#define LZMS_COST_SHIFT 5
+/* Encode a list of matches and literals chosen by the parsing algorithm.  */
+static void
+lzms_encode_item_list(struct lzms_compressor *c,
+		      struct lzms_mc_pos_data *cur_optimum_ptr)
+{
+	struct lzms_mc_pos_data *end_optimum_ptr;
+	u64 saved_item;
+	u64 item;
+
+	/* The list is currently in reverse order (last item to first item).
+	 * Reverse it.  */
+	end_optimum_ptr = cur_optimum_ptr;
+	saved_item = cur_optimum_ptr->mc_item_data;
+	do {
+		item = saved_item;
+		cur_optimum_ptr -= item & MC_LEN_MASK;
+		saved_item = cur_optimum_ptr->mc_item_data;
+		cur_optimum_ptr->mc_item_data = item;
+	} while (cur_optimum_ptr != c->optimum);
+
+	/* Walk the list of items from beginning to end, encoding each item.  */
+	do {
+		lzms_encode_item(c, cur_optimum_ptr->mc_item_data);
+		cur_optimum_ptr += (cur_optimum_ptr->mc_item_data) & MC_LEN_MASK;
+	} while (cur_optimum_ptr != end_optimum_ptr);
+}
+
+/* Each bit costs 1 << LZMS_COST_SHIFT units.  */
+#define LZMS_COST_SHIFT 6
 
 /*#define LZMS_RC_COSTS_USE_FLOATING_POINT*/
 
@@ -662,7 +705,7 @@ lzms_do_init_rc_costs(void)
 		for (u32 j = 0; j < LZMS_COST_SHIFT; j++) {
 			w *= w;
 			bit_count <<= 1;
-			while (w >= (1U << 16)) {
+			while (w >= ((u32)1 << 16)) {
 				w >>= 1;
 				++bit_count;
 			}
@@ -681,24 +724,14 @@ lzms_init_rc_costs(void)
 	pthread_once(&once, lzms_do_init_rc_costs);
 }
 
-/*
- * Return the cost to range-encode the specified bit when in the specified
- * state.
- *
- * @enc		The range encoder to use.
- * @cur_state	Current state, which indicates the probability entry to choose.
- *		Updated by this function.
- * @bit		The bit to encode (0 or 1).
- */
-static u32
-lzms_rc_bit_cost(const struct lzms_range_encoder *enc, u8 *cur_state, int bit)
+/* Return the cost to range-encode the specified bit from the specified state.*/
+static inline u32
+lzms_rc_bit_cost(const struct lzms_range_encoder *enc, u8 cur_state, int bit)
 {
 	u32 prob_zero;
 	u32 prob_correct;
 
-	prob_zero = enc->prob_entries[*cur_state & enc->mask].num_recent_zero_bits;
-
-	*cur_state = (*cur_state << 1) | bit;
+	prob_zero = enc->prob_entries[cur_state].num_recent_zero_bits;
 
 	if (bit == 0)
 		prob_correct = prob_zero;
@@ -708,447 +741,486 @@ lzms_rc_bit_cost(const struct lzms_range_encoder *enc, u8 *cur_state, int bit)
 	return lzms_rc_costs[prob_correct];
 }
 
-static u32
-lzms_huffman_symbol_cost(const struct lzms_huffman_encoder *enc, u32 sym)
+/* Return the cost to Huffman-encode the specified symbol.  */
+static inline u32
+lzms_huffman_symbol_cost(const struct lzms_huffman_encoder *enc, unsigned sym)
 {
-	return enc->lens[sym] << LZMS_COST_SHIFT;
+	return (u32)enc->lens[sym] << LZMS_COST_SHIFT;
 }
 
-static u32
-lzms_offset_cost(const struct lzms_huffman_encoder *enc, u32 offset)
+/* Return the cost to encode the specified literal byte.  */
+static inline u32
+lzms_literal_cost(const struct lzms_compressor *c, unsigned literal,
+		  const struct lzms_adaptive_state *state)
 {
-	u32 slot;
-	u32 num_extra_bits;
+	return lzms_rc_bit_cost(&c->main_range_encoder, state->main_state, 0) +
+	       lzms_huffman_symbol_cost(&c->literal_encoder, literal);
+}
+
+/* Update the table that directly provides the costs for small lengths.  */
+static void
+lzms_update_fast_length_costs(struct lzms_compressor *c)
+{
+	u32 len;
+	int slot = -1;
 	u32 cost = 0;
 
-	slot = lzms_get_position_slot(offset);
+	for (len = 1; len < LZMS_NUM_FAST_LENGTHS; len++) {
 
-	cost += lzms_huffman_symbol_cost(enc, slot);
+		while (len >= lzms_length_slot_base[slot + 1]) {
+			slot++;
+			cost = (u32)(c->length_encoder.lens[slot] +
+				     lzms_extra_length_bits[slot]) << LZMS_COST_SHIFT;
+		}
 
-	num_extra_bits = lzms_extra_position_bits[slot];
+		c->length_cost_fast[len] = cost;
+	}
+}
+
+/* Return the cost to encode the specified match length, which must be less than
+ * LZMS_NUM_FAST_LENGTHS.  */
+static inline u32
+lzms_fast_length_cost(const struct lzms_compressor *c, u32 length)
+{
+	LZMS_ASSERT(length < LZMS_NUM_FAST_LENGTHS);
+	return c->length_cost_fast[length];
+}
 
-	cost += num_extra_bits << LZMS_COST_SHIFT;
+/* Return the cost to encode the specified LZ match offset.  */
+static inline u32
+lzms_lz_offset_cost(const struct lzms_compressor *c, u32 offset)
+{
+	unsigned slot = lzms_get_offset_slot_fast(c, offset);
 
-	return cost;
+	return (u32)(c->lz_offset_encoder.lens[slot] +
+		     lzms_extra_offset_bits[slot]) << LZMS_COST_SHIFT;
 }
 
-static u32
-lzms_get_length_cost(const struct lzms_huffman_encoder *enc, u32 length)
+/*
+ * Consider coding the match at repeat offset index @rep_idx.  Consider each
+ * length from the minimum (2) to the full match length (@rep_len).
+ */
+static inline void
+lzms_consider_lz_repeat_offset_match(const struct lzms_compressor *c,
+				     struct lzms_mc_pos_data *cur_optimum_ptr,
+				     u32 rep_len, unsigned rep_idx)
 {
-	u32 slot;
-	u32 num_extra_bits;
-	u32 cost = 0;
+	u32 len;
+	u32 base_cost;
+	u32 cost;
+	unsigned i;
 
-	slot = lzms_get_length_slot(length);
+	base_cost = cur_optimum_ptr->cost;
 
-	cost += lzms_huffman_symbol_cost(enc, slot);
+	base_cost += lzms_rc_bit_cost(&c->main_range_encoder,
+				      cur_optimum_ptr->state.main_state, 1);
 
-	num_extra_bits = lzms_extra_length_bits[slot];
+	base_cost += lzms_rc_bit_cost(&c->match_range_encoder,
+				      cur_optimum_ptr->state.match_state, 0);
+
+	base_cost += lzms_rc_bit_cost(&c->lz_match_range_encoder,
+				      cur_optimum_ptr->state.lz_match_state, 1);
+
+	for (i = 0; i < rep_idx; i++)
+		base_cost += lzms_rc_bit_cost(&c->lz_repeat_match_range_encoders[i],
+					      cur_optimum_ptr->state.lz_repeat_match_state[i], 1);
 
-	cost += num_extra_bits << LZMS_COST_SHIFT;
+	if (i < LZMS_NUM_RECENT_OFFSETS - 1)
+		base_cost += lzms_rc_bit_cost(&c->lz_repeat_match_range_encoders[i],
+					      cur_optimum_ptr->state.lz_repeat_match_state[i], 0);
 
-	return cost;
+	len = 2;
+	do {
+		cost = base_cost + lzms_fast_length_cost(c, len);
+		if (cost < (cur_optimum_ptr + len)->cost) {
+			(cur_optimum_ptr + len)->mc_item_data =
+				((u64)rep_idx << MC_OFFSET_SHIFT) | len;
+			(cur_optimum_ptr + len)->cost = cost;
+		}
+	} while (++len <= rep_len);
 }
 
-static u32
-lzms_get_matches(struct lzms_compressor *ctx, struct lz_match **matches_ret)
+/*
+ * Consider coding each match in @matches as an explicit offset match.
+ *
+ * @matches must be sorted by strictly increasing length and strictly increasing
+ * offset.  This is guaranteed by the match-finder.
+ *
+ * We consider each length from the minimum (2) to the longest
+ * (matches[num_matches - 1].len).  For each length, we consider only the
+ * smallest offset for which that length is available.  Although this is not
+ * guaranteed to be optimal due to the possibility of a larger offset costing
+ * less than a smaller offset to code, this is a very useful heuristic.
+ */
+static inline void
+lzms_consider_lz_explicit_offset_matches(const struct lzms_compressor *c,
+					 struct lzms_mc_pos_data *cur_optimum_ptr,
+					 const struct lz_match matches[],
+					 u32 num_matches)
 {
-	*matches_ret = ctx->matches;
-	return lz_mf_get_matches(ctx->mf, ctx->matches);
+	u32 len;
+	u32 i;
+	u32 base_cost;
+	u32 position_cost;
+	u32 cost;
+
+	base_cost = cur_optimum_ptr->cost;
+
+	base_cost += lzms_rc_bit_cost(&c->main_range_encoder,
+				      cur_optimum_ptr->state.main_state, 1);
+
+	base_cost += lzms_rc_bit_cost(&c->match_range_encoder,
+				      cur_optimum_ptr->state.match_state, 0);
+
+	base_cost += lzms_rc_bit_cost(&c->lz_match_range_encoder,
+				      cur_optimum_ptr->state.lz_match_state, 0);
+	len = 2;
+	i = 0;
+	do {
+		position_cost = base_cost + lzms_lz_offset_cost(c, matches[i].offset);
+		do {
+			cost = position_cost + lzms_fast_length_cost(c, len);
+			if (cost < (cur_optimum_ptr + len)->cost) {
+				(cur_optimum_ptr + len)->mc_item_data =
+					((u64)(matches[i].offset + LZMS_OFFSET_OFFSET)
+						<< MC_OFFSET_SHIFT) | len;
+				(cur_optimum_ptr + len)->cost = cost;
+			}
+		} while (++len <= matches[i].len);
+	} while (++i != num_matches);
 }
 
 static void
-lzms_skip_bytes(struct lzms_compressor *ctx, u32 n)
+lzms_init_adaptive_state(struct lzms_adaptive_state *state)
 {
-	lz_mf_skip_positions(ctx->mf, n);
+	unsigned i;
+
+	lzms_init_lz_lru_queues(&state->lru);
+	state->main_state = 0;
+	state->match_state = 0;
+	state->lz_match_state = 0;
+	for (i = 0; i < LZMS_NUM_RECENT_OFFSETS - 1; i++)
+		state->lz_repeat_match_state[i] = 0;
 }
 
-static u32
-lzms_get_literal_cost(struct lzms_compressor *ctx,
-		      struct lzms_adaptive_state *state, u8 literal)
+static inline void
+lzms_update_main_state(struct lzms_adaptive_state *state, int is_match)
 {
-	u32 cost = 0;
-
-	state->lru.upcoming_offset = 0;
-	lzms_update_lz_lru_queues(&state->lru);
-
-	cost += lzms_rc_bit_cost(&ctx->main_range_encoder,
-				 &state->main_state, 0);
-
-	cost += lzms_huffman_symbol_cost(&ctx->literal_encoder, literal);
+	state->main_state = ((state->main_state << 1) | is_match) % LZMS_NUM_MAIN_STATES;
+}
 
-	return cost;
+static inline void
+lzms_update_match_state(struct lzms_adaptive_state *state, int is_delta)
+{
+	state->match_state = ((state->match_state << 1) | is_delta) % LZMS_NUM_MATCH_STATES;
 }
 
-static u32
-lzms_get_lz_match_cost_nolen(struct lzms_compressor *ctx,
-			     struct lzms_adaptive_state *state, u32 offset)
+static inline void
+lzms_update_lz_match_state(struct lzms_adaptive_state *state, int is_repeat_offset)
 {
-	u32 cost = 0;
-	int recent_offset_idx;
+	state->lz_match_state = ((state->lz_match_state << 1) | is_repeat_offset) % LZMS_NUM_LZ_MATCH_STATES;
+}
 
-	cost += lzms_rc_bit_cost(&ctx->main_range_encoder,
-				 &state->main_state, 1);
-	cost += lzms_rc_bit_cost(&ctx->match_range_encoder,
-				 &state->match_state, 0);
+static inline void
+lzms_update_lz_repeat_match_state(struct lzms_adaptive_state *state, int rep_idx)
+{
+	int i;
 
-	for (recent_offset_idx = 0;
-	     recent_offset_idx < LZMS_NUM_RECENT_OFFSETS;
-	     recent_offset_idx++)
-		if (offset == state->lru.recent_offsets[recent_offset_idx])
-			break;
+	for (i = 0; i < rep_idx; i++)
+		state->lz_repeat_match_state[i] =
+			((state->lz_repeat_match_state[i] << 1) | 1) %
+				LZMS_NUM_LZ_REPEAT_MATCH_STATES;
 
-	if (recent_offset_idx == LZMS_NUM_RECENT_OFFSETS) {
-		/* Explicit offset.  */
-		cost += lzms_rc_bit_cost(&ctx->lz_match_range_encoder,
-					 &state->lz_match_state, 0);
+	if (i < LZMS_NUM_RECENT_OFFSETS - 1)
+		state->lz_repeat_match_state[i] =
+			((state->lz_repeat_match_state[i] << 1) | 0) %
+				LZMS_NUM_LZ_REPEAT_MATCH_STATES;
+}
 
-		cost += lzms_offset_cost(&ctx->lz_offset_encoder, offset);
-	} else {
-		int i;
+/*
+ * The main near-optimal parsing routine.
+ *
+ * Briefly, the algorithm does an approximate minimum-cost path search to find a
+ * "near-optimal" sequence of matches and literals to output, based on the
+ * current cost model.  The algorithm steps forward, position by position (byte
+ * by byte), and updates the minimum cost path to reach each later position that
+ * can be reached using a match or literal from the current position.  This is
+ * essentially Dijkstra's algorithm in disguise: the graph nodes are positions,
+ * the graph edges are possible matches/literals to code, and the cost of each
+ * edge is the estimated number of bits that will be required to output the
+ * corresponding match or literal.  But one difference is that we actually
+ * compute the lowest-cost path in pieces, where each piece is terminated when
+ * there are no choices to be made.
+ *
+ * Notes:
+ *
+ * - This does not output any delta matches.
+ *
+ * - The costs of literals and matches are estimated using the range encoder
+ *   states and the semi-adaptive Huffman codes.  Except for range encoding
+ *   states, costs are assumed to be constant throughout a single run of the
+ *   parsing algorithm, which can parse up to @optim_array_length bytes of data.
+ *   This introduces a source of inaccuracy because the probabilities and
+ *   Huffman codes can change over this part of the data.
+ */
+static void
+lzms_near_optimal_parse(struct lzms_compressor *c)
+{
+	const u8 *window_ptr;
+	const u8 *window_end;
+	struct lzms_mc_pos_data *cur_optimum_ptr;
+	struct lzms_mc_pos_data *end_optimum_ptr;
+	u32 num_matches;
+	u32 longest_len;
+	u32 rep_max_len;
+	unsigned rep_max_idx;
+	unsigned literal;
+	unsigned i;
+	u32 cost;
+	u32 len;
+	u32 offset_data;
 
-		/* Recent offset.  */
-		cost += lzms_rc_bit_cost(&ctx->lz_match_range_encoder,
-					 &state->lz_match_state, 1);
+	window_ptr = c->cur_window;
+	window_end = window_ptr + c->cur_window_size;
 
-		for (i = 0; i < recent_offset_idx; i++)
-			cost += lzms_rc_bit_cost(&ctx->lz_repeat_match_range_encoders[i],
-						 &state->lz_repeat_match_state[i], 0);
+	lzms_init_adaptive_state(&c->optimum[0].state);
 
-		if (i < LZMS_NUM_RECENT_OFFSETS - 1)
-			cost += lzms_rc_bit_cost(&ctx->lz_repeat_match_range_encoders[i],
-						 &state->lz_repeat_match_state[i], 1);
+begin:
+	/* Start building a new list of items, which will correspond to the next
+	 * piece of the overall minimum-cost path.  */
 
+	cur_optimum_ptr = c->optimum;
+	cur_optimum_ptr->cost = 0;
+	end_optimum_ptr = cur_optimum_ptr;
 
-		/* Initial update of the LZ match offset LRU queue.  */
-		for (; i < LZMS_NUM_RECENT_OFFSETS; i++)
-			state->lru.recent_offsets[i] = state->lru.recent_offsets[i + 1];
-	}
+	/* States should currently be consistent with the encoders.  */
+	LZMS_ASSERT(cur_optimum_ptr->state.main_state == c->main_range_encoder.state);
+	LZMS_ASSERT(cur_optimum_ptr->state.match_state == c->match_range_encoder.state);
+	LZMS_ASSERT(cur_optimum_ptr->state.lz_match_state == c->lz_match_range_encoder.state);
+	for (i = 0; i < LZMS_NUM_RECENT_OFFSETS - 1; i++)
+		LZMS_ASSERT(cur_optimum_ptr->state.lz_repeat_match_state[i] ==
+			    c->lz_repeat_match_range_encoders[i].state);
 
+	if (window_ptr == window_end)
+		return;
 
-	state->lru.upcoming_offset = offset;
-	lzms_update_lz_lru_queues(&state->lru);
+	/* The following loop runs once for each per byte in the window, except
+	 * in a couple shortcut cases.  */
+	for (;;) {
 
-	return cost;
-}
+		/* Find explicit offset matches with the current position.  */
+		num_matches = lz_mf_get_matches(c->mf, c->matches);
 
-static u32
-lzms_get_lz_match_cost(struct lzms_compressor *ctx,
-		       struct lzms_adaptive_state *state,
-		       u32 length, u32 offset)
-{
-	return lzms_get_lz_match_cost_nolen(ctx, state, offset) +
-	       lzms_get_length_cost(&ctx->length_encoder, length);
-}
+		if (num_matches) {
+			/*
+			 * Find the longest repeat offset match with the current
+			 * position.
+			 *
+			 * Heuristics:
+			 *
+			 * - Only search for repeat offset matches if the
+			 *   match-finder already found at least one match.
+			 *
+			 * - Only consider the longest repeat offset match.  It
+			 *   seems to be rare for the optimal parse to include a
+			 *   repeat offset match that doesn't have the longest
+			 *   length (allowing for the possibility that not all
+			 *   of that length is actually used).
+			 */
+			if (likely(window_ptr - c->cur_window >= LZMS_MAX_INIT_RECENT_OFFSET)) {
+				BUILD_BUG_ON(LZMS_NUM_RECENT_OFFSETS != 3);
+				rep_max_len = lz_repsearch3(window_ptr,
+							    window_end - window_ptr,
+							    cur_optimum_ptr->state.lru.recent_offsets,
+							    &rep_max_idx);
+			} else {
+				rep_max_len = 0;
+			}
 
-static struct lz_match
-lzms_match_chooser_reverse_list(struct lzms_compressor *ctx, unsigned cur_pos)
-{
-	unsigned prev_link, saved_prev_link;
-	unsigned prev_match_offset, saved_prev_match_offset;
+			if (rep_max_len) {
+				/* If there's a very long repeat offset match,
+				 * choose it immediately.  */
+				if (rep_max_len >= c->params.nice_match_length) {
 
-	ctx->optimum_end_idx = cur_pos;
+					lz_mf_skip_positions(c->mf, rep_max_len - 1);
+					window_ptr += rep_max_len;
 
-	saved_prev_link = ctx->optimum[cur_pos].prev.link;
-	saved_prev_match_offset = ctx->optimum[cur_pos].prev.match_offset;
+					if (cur_optimum_ptr != c->optimum)
+						lzms_encode_item_list(c, cur_optimum_ptr);
 
-	do {
-		prev_link = saved_prev_link;
-		prev_match_offset = saved_prev_match_offset;
+					lzms_encode_lz_repeat_offset_match(c, rep_max_len,
+									   rep_max_idx);
 
-		saved_prev_link = ctx->optimum[prev_link].prev.link;
-		saved_prev_match_offset = ctx->optimum[prev_link].prev.match_offset;
+					c->optimum[0].state = cur_optimum_ptr->state;
 
-		ctx->optimum[prev_link].next.link = cur_pos;
-		ctx->optimum[prev_link].next.match_offset = prev_match_offset;
+					lzms_update_main_state(&c->optimum[0].state, 1);
+					lzms_update_match_state(&c->optimum[0].state, 0);
+					lzms_update_lz_match_state(&c->optimum[0].state, 1);
+					lzms_update_lz_repeat_match_state(&c->optimum[0].state,
+									  rep_max_idx);
 
-		cur_pos = prev_link;
-	} while (cur_pos != 0);
+					c->optimum[0].state.lru.upcoming_offset =
+						c->optimum[0].state.lru.recent_offsets[rep_max_idx];
 
-	ctx->optimum_cur_idx = ctx->optimum[0].next.link;
+					for (i = rep_max_idx; i < LZMS_NUM_RECENT_OFFSETS; i++)
+						c->optimum[0].state.lru.recent_offsets[i] =
+							c->optimum[0].state.lru.recent_offsets[i + 1];
 
-	return (struct lz_match)
-		{ .len = ctx->optimum_cur_idx,
-		  .offset = ctx->optimum[0].next.match_offset,
-		};
-}
+					lzms_update_lz_lru_queue(&c->optimum[0].state.lru);
+					goto begin;
+				}
 
-/* This is similar to lzx_choose_near_optimal_item() in lzx-compress.c.
- * Read that one if you want to understand it.  */
-static struct lz_match
-lzms_get_near_optimal_item(struct lzms_compressor *ctx)
-{
-	u32 num_matches;
-	struct lz_match *matches;
-	struct lz_match match;
-	u32 longest_len;
-	u32 longest_rep_len;
-	u32 longest_rep_offset;
-	unsigned cur_pos;
-	unsigned end_pos;
-	struct lzms_adaptive_state initial_state;
-
-	if (ctx->optimum_cur_idx != ctx->optimum_end_idx) {
-		match.len = ctx->optimum[ctx->optimum_cur_idx].next.link -
-				    ctx->optimum_cur_idx;
-		match.offset = ctx->optimum[ctx->optimum_cur_idx].next.match_offset;
-
-		ctx->optimum_cur_idx = ctx->optimum[ctx->optimum_cur_idx].next.link;
-		return match;
-	}
+				/* If reaching any positions for the first time,
+				 * initialize their costs to "infinity".  */
+				while (end_optimum_ptr < cur_optimum_ptr + rep_max_len)
+					(++end_optimum_ptr)->cost = MC_INFINITE_COST;
 
-	ctx->optimum_cur_idx = 0;
-	ctx->optimum_end_idx = 0;
-
-	longest_rep_len = ctx->params.min_match_length - 1;
-	if (lz_mf_get_position(ctx->mf) >= LZMS_MAX_INIT_RECENT_OFFSET) {
-		u32 limit = lz_mf_get_bytes_remaining(ctx->mf);
-		for (int i = 0; i < LZMS_NUM_RECENT_OFFSETS; i++) {
-			u32 offset = ctx->lru.lz.recent_offsets[i];
-			const u8 *strptr = lz_mf_get_window_ptr(ctx->mf);
-			const u8 *matchptr = strptr - offset;
-			u32 len = 0;
-			while (len < limit && strptr[len] == matchptr[len])
-				len++;
-			if (len > longest_rep_len) {
-				longest_rep_len = len;
-				longest_rep_offset = offset;
+				/* Consider coding a repeat offset match.  */
+				lzms_consider_lz_repeat_offset_match(c, cur_optimum_ptr,
+								     rep_max_len, rep_max_idx);
 			}
-		}
-	}
 
-	if (longest_rep_len >= ctx->params.nice_match_length) {
-		lzms_skip_bytes(ctx, longest_rep_len);
-		return (struct lz_match) {
-			.len = longest_rep_len,
-			.offset = longest_rep_offset,
-		};
-	}
+			longest_len = c->matches[num_matches - 1].len;
 
-	num_matches = lzms_get_matches(ctx, &matches);
+			/* If there's a very long explicit offset match, choose
+			 * it immediately.  */
+			if (longest_len >= c->params.nice_match_length) {
 
-	if (num_matches) {
-		longest_len = matches[num_matches - 1].len;
-		if (longest_len >= ctx->params.nice_match_length) {
-			lzms_skip_bytes(ctx, longest_len - 1);
-			return matches[num_matches - 1];
-		}
-	} else {
-		longest_len = 1;
-	}
+				lz_mf_skip_positions(c->mf, longest_len - 1);
+				window_ptr += longest_len;
 
-	initial_state.lru = ctx->lru.lz;
-	initial_state.main_state = ctx->main_range_encoder.state;
-	initial_state.match_state = ctx->match_range_encoder.state;
-	initial_state.lz_match_state = ctx->lz_match_range_encoder.state;
-	for (int i = 0; i < LZMS_NUM_RECENT_OFFSETS - 1; i++)
-		initial_state.lz_repeat_match_state[i] = ctx->lz_repeat_match_range_encoders[i].state;
+				if (cur_optimum_ptr != c->optimum)
+					lzms_encode_item_list(c, cur_optimum_ptr);
 
-	ctx->optimum[1].state = initial_state;
-	ctx->optimum[1].cost = lzms_get_literal_cost(ctx,
-						     &ctx->optimum[1].state,
-						     *(lz_mf_get_window_ptr(ctx->mf) - 1));
-	ctx->optimum[1].prev.link = 0;
+				lzms_encode_lz_explicit_offset_match(c, longest_len,
+								     c->matches[num_matches - 1].offset);
 
-	for (u32 i = 0, len = 2; i < num_matches; i++) {
-		u32 offset = matches[i].offset;
-		struct lzms_adaptive_state state;
-		u32 position_cost;
+				c->optimum[0].state = cur_optimum_ptr->state;
 
-		state = initial_state;
-		position_cost = 0;
-		position_cost += lzms_get_lz_match_cost_nolen(ctx, &state, offset);
+				lzms_update_main_state(&c->optimum[0].state, 1);
+				lzms_update_match_state(&c->optimum[0].state, 0);
+				lzms_update_lz_match_state(&c->optimum[0].state, 0);
 
-		do {
-			u32 cost;
+				c->optimum[0].state.lru.upcoming_offset =
+					c->matches[num_matches - 1].offset;
 
-			cost = position_cost;
-			cost += lzms_get_length_cost(&ctx->length_encoder, len);
+				lzms_update_lz_lru_queue(&c->optimum[0].state.lru);
+				goto begin;
+			}
 
-			ctx->optimum[len].state = state;
-			ctx->optimum[len].prev.link = 0;
-			ctx->optimum[len].prev.match_offset = offset;
-			ctx->optimum[len].cost = cost;
-		} while (++len <= matches[i].len);
-	}
-	end_pos = longest_len;
-
-	if (longest_rep_len >= ctx->params.min_match_length) {
-		struct lzms_adaptive_state state;
-		u32 cost;
-
-		while (end_pos < longest_rep_len)
-			ctx->optimum[++end_pos].cost = MC_INFINITE_COST;
-
-		state = initial_state;
-		cost = lzms_get_lz_match_cost(ctx,
-					      &state,
-					      longest_rep_len,
-					      longest_rep_offset);
-		if (cost <= ctx->optimum[longest_rep_len].cost) {
-			ctx->optimum[longest_rep_len].state = state;
-			ctx->optimum[longest_rep_len].prev.link = 0;
-			ctx->optimum[longest_rep_len].prev.match_offset = longest_rep_offset;
-			ctx->optimum[longest_rep_len].cost = cost;
-		}
-	}
+			/* If reaching any positions for the first time,
+			 * initialize their costs to "infinity".  */
+			while (end_optimum_ptr < cur_optimum_ptr + longest_len)
+				(++end_optimum_ptr)->cost = MC_INFINITE_COST;
 
-	cur_pos = 0;
-	for (;;) {
-		u32 cost;
-		struct lzms_adaptive_state state;
-
-		cur_pos++;
-
-		if (cur_pos == end_pos || cur_pos == ctx->params.optim_array_length)
-			return lzms_match_chooser_reverse_list(ctx, cur_pos);
-
-		longest_rep_len = ctx->params.min_match_length - 1;
-		if (lz_mf_get_position(ctx->mf) >= LZMS_MAX_INIT_RECENT_OFFSET) {
-			u32 limit = lz_mf_get_bytes_remaining(ctx->mf);
-			for (int i = 0; i < LZMS_NUM_RECENT_OFFSETS; i++) {
-				u32 offset = ctx->optimum[cur_pos].state.lru.recent_offsets[i];
-				const u8 *strptr = lz_mf_get_window_ptr(ctx->mf);
-				const u8 *matchptr = strptr - offset;
-				u32 len = 0;
-				while (len < limit && strptr[len] == matchptr[len])
-					len++;
-				if (len > longest_rep_len) {
-					longest_rep_len = len;
-					longest_rep_offset = offset;
-				}
-			}
-		}
+			/* Consider coding an explicit offset match.  */
+			lzms_consider_lz_explicit_offset_matches(c, cur_optimum_ptr,
+								 c->matches, num_matches);
+		} else {
+			/* No matches found.  The only choice at this position
+			 * is to code a literal.  */
 
-		if (longest_rep_len >= ctx->params.nice_match_length) {
-			match = lzms_match_chooser_reverse_list(ctx, cur_pos);
+			if (end_optimum_ptr == cur_optimum_ptr)
+				(++end_optimum_ptr)->cost = MC_INFINITE_COST;
+		}
 
-			ctx->optimum[cur_pos].next.match_offset = longest_rep_offset;
-			ctx->optimum[cur_pos].next.link = cur_pos + longest_rep_len;
-			ctx->optimum_end_idx = cur_pos + longest_rep_len;
+		/* Consider coding a literal.
 
-			lzms_skip_bytes(ctx, longest_rep_len);
+		 * To avoid an extra unpredictable brench, actually checking the
+		 * preferability of coding a literal is integrated into the
+		 * adaptive state update code below.  */
+		literal = *window_ptr++;
+		cost = cur_optimum_ptr->cost +
+		       lzms_literal_cost(c, literal, &cur_optimum_ptr->state);
 
-			return match;
-		}
+		/* Advance to the next position.  */
+		cur_optimum_ptr++;
 
-		num_matches = lzms_get_matches(ctx, &matches);
+		/* The lowest-cost path to the current position is now known.
+		 * Finalize the adaptive state that results from taking this
+		 * lowest-cost path.  */
 
-		if (num_matches) {
-			longest_len = matches[num_matches - 1].len;
-			if (longest_len >= ctx->params.nice_match_length) {
-				match = lzms_match_chooser_reverse_list(ctx, cur_pos);
+		if (cost < cur_optimum_ptr->cost) {
+			/* Literal  */
+			cur_optimum_ptr->cost = cost;
+			cur_optimum_ptr->mc_item_data = ((u64)literal << MC_OFFSET_SHIFT) | 1;
 
-				ctx->optimum[cur_pos].next.match_offset =
-					matches[num_matches - 1].offset;
-				ctx->optimum[cur_pos].next.link = cur_pos + longest_len;
-				ctx->optimum_end_idx = cur_pos + longest_len;
+			cur_optimum_ptr->state = (cur_optimum_ptr - 1)->state;
 
-				lzms_skip_bytes(ctx, longest_len - 1);
+			lzms_update_main_state(&cur_optimum_ptr->state, 0);
 
-				return match;
-			}
+			cur_optimum_ptr->state.lru.upcoming_offset = 0;
 		} else {
-			longest_len = 1;
-		}
+			/* LZ match  */
+			len = cur_optimum_ptr->mc_item_data & MC_LEN_MASK;
+			offset_data = cur_optimum_ptr->mc_item_data >> MC_OFFSET_SHIFT;
 
-		while (end_pos < cur_pos + longest_len)
-			ctx->optimum[++end_pos].cost = MC_INFINITE_COST;
-
-		state = ctx->optimum[cur_pos].state;
-		cost = ctx->optimum[cur_pos].cost +
-			lzms_get_literal_cost(ctx,
-					      &state,
-					      *(lz_mf_get_window_ptr(ctx->mf) - 1));
-		if (cost < ctx->optimum[cur_pos + 1].cost) {
-			ctx->optimum[cur_pos + 1].state = state;
-			ctx->optimum[cur_pos + 1].cost = cost;
-			ctx->optimum[cur_pos + 1].prev.link = cur_pos;
-		}
-
-		for (u32 i = 0, len = 2; i < num_matches; i++) {
-			u32 offset = matches[i].offset;
-			struct lzms_adaptive_state state;
-			u32 position_cost;
+			cur_optimum_ptr->state = (cur_optimum_ptr - len)->state;
 
-			state = ctx->optimum[cur_pos].state;
-			position_cost = ctx->optimum[cur_pos].cost;
-			position_cost += lzms_get_lz_match_cost_nolen(ctx, &state, offset);
+			lzms_update_main_state(&cur_optimum_ptr->state, 1);
+			lzms_update_match_state(&cur_optimum_ptr->state, 0);
 
-			do {
-				u32 cost;
+			if (offset_data >= LZMS_NUM_RECENT_OFFSETS) {
 
-				cost = position_cost;
-				cost += lzms_get_length_cost(&ctx->length_encoder, len);
+				/* Explicit offset LZ match  */
 
-				if (cost < ctx->optimum[cur_pos + len].cost) {
-					ctx->optimum[cur_pos + len].state = state;
-					ctx->optimum[cur_pos + len].prev.link = cur_pos;
-					ctx->optimum[cur_pos + len].prev.match_offset = offset;
-					ctx->optimum[cur_pos + len].cost = cost;
-				}
-			} while (++len <= matches[i].len);
-		}
+				lzms_update_lz_match_state(&cur_optimum_ptr->state, 0);
 
-		if (longest_rep_len >= ctx->params.min_match_length) {
-
-			while (end_pos < cur_pos + longest_rep_len)
-				ctx->optimum[++end_pos].cost = MC_INFINITE_COST;
-
-			state = ctx->optimum[cur_pos].state;
-
-			cost = ctx->optimum[cur_pos].cost +
-				lzms_get_lz_match_cost(ctx,
-						       &state,
-						       longest_rep_len,
-						       longest_rep_offset);
-			if (cost <= ctx->optimum[cur_pos + longest_rep_len].cost) {
-				ctx->optimum[cur_pos + longest_rep_len].state =
-					state;
-				ctx->optimum[cur_pos + longest_rep_len].prev.link =
-					cur_pos;
-				ctx->optimum[cur_pos + longest_rep_len].prev.match_offset =
-					longest_rep_offset;
-				ctx->optimum[cur_pos + longest_rep_len].cost =
-					cost;
-			}
-		}
-	}
-}
+				cur_optimum_ptr->state.lru.upcoming_offset =
+					offset_data - LZMS_OFFSET_OFFSET;
+			} else {
+				/* Repeat offset LZ match  */
 
-/*
- * The main loop for the LZMS compressor.
- *
- * Notes:
- *
- * - This does not output any delta matches.
- *
- * - The costs of literals and matches are estimated using the range encoder
- *   states and the semi-adaptive Huffman codes.  Except for range encoding
- *   states, costs are assumed to be constant throughout a single run of the
- *   parsing algorithm, which can parse up to @optim_array_length bytes of data.
- *   This introduces a source of inaccuracy because the probabilities and
- *   Huffman codes can change over this part of the data.
- */
-static void
-lzms_encode(struct lzms_compressor *ctx)
-{
-	struct lz_match item;
+				lzms_update_lz_match_state(&cur_optimum_ptr->state, 1);
+				lzms_update_lz_repeat_match_state(&cur_optimum_ptr->state,
+								  offset_data);
 
-	/* Load window into the match-finder.  */
-	lz_mf_load_window(ctx->mf, ctx->window, ctx->window_size);
+				cur_optimum_ptr->state.lru.upcoming_offset =
+					cur_optimum_ptr->state.lru.recent_offsets[offset_data];
 
-	/* Reset the match-chooser.  */
-	ctx->optimum_cur_idx = 0;
-	ctx->optimum_end_idx = 0;
+				for (i = offset_data; i < LZMS_NUM_RECENT_OFFSETS; i++)
+					cur_optimum_ptr->state.lru.recent_offsets[i] =
+						cur_optimum_ptr->state.lru.recent_offsets[i + 1];
+			}
+		}
 
-	while (ctx->cur_window_pos != ctx->window_size) {
-		item = lzms_get_near_optimal_item(ctx);
-		if (item.len <= 1)
-			lzms_encode_literal(ctx, ctx->window[ctx->cur_window_pos]);
-		else
-			lzms_encode_lz_match(ctx, item.len, item.offset);
+		lzms_update_lz_lru_queue(&cur_optimum_ptr->state.lru);
+
+		/*
+		 * This loop will terminate when either of the following
+		 * conditions is true:
+		 *
+		 * (1) cur_optimum_ptr == end_optimum_ptr
+		 *
+		 *	There are no paths that extend beyond the current
+		 *	position.  In this case, any path to a later position
+		 *	must pass through the current position, so we can go
+		 *	ahead and choose the list of items that led to this
+		 *	position.
+		 *
+		 * (2) cur_optimum_ptr == c->optimum_end
+		 *
+		 *	This bounds the number of times the algorithm can step
+		 *	forward before it is guaranteed to start choosing items.
+		 *	This limits the memory usage.  It also guarantees that
+		 *	the parser will not go too long without updating the
+		 *	probability tables.
+		 *
+		 * Note: no check for end-of-window is needed because
+		 * end-of-window will trigger condition (1).
+		 */
+		if (cur_optimum_ptr == end_optimum_ptr ||
+		    cur_optimum_ptr == c->optimum_end)
+		{
+			c->optimum[0].state = cur_optimum_ptr->state;
+			break;
+		}
 	}
+
+	/* Output the current list of items that constitute the minimum-cost
+	 * path to the current position.  */
+	lzms_encode_item_list(c, cur_optimum_ptr);
+	goto begin;
 }
 
 static void
@@ -1157,6 +1229,7 @@ lzms_init_range_encoder(struct lzms_range_encoder *enc,
 {
 	enc->rc = rc;
 	enc->state = 0;
+	LZMS_ASSERT(is_power_of_2(num_states));
 	enc->mask = num_states - 1;
 	for (u32 i = 0; i < num_states; i++) {
 		enc->prob_entries[i].num_recent_zero_bits = LZMS_INITIAL_PROBABILITY;
@@ -1184,77 +1257,72 @@ lzms_init_huffman_encoder(struct lzms_huffman_encoder *enc,
 				    enc->codewords);
 }
 
-/* Initialize the LZMS compressor.  */
+/* Prepare the LZMS compressor for compressing a block of data.  */
 static void
-lzms_init_compressor(struct lzms_compressor *ctx, const u8 *udata, u32 ulen,
-		     le16 *cdata, u32 clen16)
+lzms_prepare_compressor(struct lzms_compressor *c, const u8 *udata, u32 ulen,
+			le16 *cdata, u32 clen16)
 {
-	unsigned num_position_slots;
+	unsigned num_offset_slots;
 
-	/* Copy the uncompressed data into the @ctx->window buffer.  */
-	memcpy(ctx->window, udata, ulen);
-	ctx->cur_window_pos = 0;
-	ctx->window_size = ulen;
+	/* Copy the uncompressed data into the @c->cur_window buffer.  */
+	memcpy(c->cur_window, udata, ulen);
+	c->cur_window_size = ulen;
 
 	/* Initialize the raw range encoder (writing forwards).  */
-	lzms_range_encoder_raw_init(&ctx->rc, cdata, clen16);
+	lzms_range_encoder_raw_init(&c->rc, cdata, clen16);
 
 	/* Initialize the output bitstream for Huffman symbols and verbatim bits
 	 * (writing backwards).  */
-	lzms_output_bitstream_init(&ctx->os, cdata, clen16);
-
-	/* Calculate the number of position slots needed for this compressed
-	 * block.  */
-	num_position_slots = lzms_get_position_slot(ulen - 1) + 1;
+	lzms_output_bitstream_init(&c->os, cdata, clen16);
 
-	LZMS_DEBUG("Using %u position slots", num_position_slots);
+	/* Calculate the number of offset slots required.  */
+	num_offset_slots = lzms_get_offset_slot(ulen - 1) + 1;
 
-	/* Initialize Huffman encoders for each alphabet used in the compressed
-	 * representation.  */
-	lzms_init_huffman_encoder(&ctx->literal_encoder, &ctx->os,
+	/* Initialize a Huffman encoder for each alphabet.  */
+	lzms_init_huffman_encoder(&c->literal_encoder, &c->os,
 				  LZMS_NUM_LITERAL_SYMS,
 				  LZMS_LITERAL_CODE_REBUILD_FREQ);
 
-	lzms_init_huffman_encoder(&ctx->lz_offset_encoder, &ctx->os,
-				  num_position_slots,
+	lzms_init_huffman_encoder(&c->lz_offset_encoder, &c->os,
+				  num_offset_slots,
 				  LZMS_LZ_OFFSET_CODE_REBUILD_FREQ);
 
-	lzms_init_huffman_encoder(&ctx->length_encoder, &ctx->os,
+	lzms_init_huffman_encoder(&c->length_encoder, &c->os,
 				  LZMS_NUM_LEN_SYMS,
 				  LZMS_LENGTH_CODE_REBUILD_FREQ);
 
-	lzms_init_huffman_encoder(&ctx->delta_offset_encoder, &ctx->os,
-				  num_position_slots,
+	lzms_init_huffman_encoder(&c->delta_offset_encoder, &c->os,
+				  num_offset_slots,
 				  LZMS_DELTA_OFFSET_CODE_REBUILD_FREQ);
 
-	lzms_init_huffman_encoder(&ctx->delta_power_encoder, &ctx->os,
+	lzms_init_huffman_encoder(&c->delta_power_encoder, &c->os,
 				  LZMS_NUM_DELTA_POWER_SYMS,
 				  LZMS_DELTA_POWER_CODE_REBUILD_FREQ);
 
 	/* Initialize range encoders, all of which wrap around the same
 	 * lzms_range_encoder_raw.  */
-	lzms_init_range_encoder(&ctx->main_range_encoder,
-				&ctx->rc, LZMS_NUM_MAIN_STATES);
+	lzms_init_range_encoder(&c->main_range_encoder,
+				&c->rc, LZMS_NUM_MAIN_STATES);
 
-	lzms_init_range_encoder(&ctx->match_range_encoder,
-				&ctx->rc, LZMS_NUM_MATCH_STATES);
+	lzms_init_range_encoder(&c->match_range_encoder,
+				&c->rc, LZMS_NUM_MATCH_STATES);
 
-	lzms_init_range_encoder(&ctx->lz_match_range_encoder,
-				&ctx->rc, LZMS_NUM_LZ_MATCH_STATES);
+	lzms_init_range_encoder(&c->lz_match_range_encoder,
+				&c->rc, LZMS_NUM_LZ_MATCH_STATES);
 
-	for (size_t i = 0; i < ARRAY_LEN(ctx->lz_repeat_match_range_encoders); i++)
-		lzms_init_range_encoder(&ctx->lz_repeat_match_range_encoders[i],
-					&ctx->rc, LZMS_NUM_LZ_REPEAT_MATCH_STATES);
+	for (unsigned i = 0; i < ARRAY_LEN(c->lz_repeat_match_range_encoders); i++)
+		lzms_init_range_encoder(&c->lz_repeat_match_range_encoders[i],
+					&c->rc, LZMS_NUM_LZ_REPEAT_MATCH_STATES);
 
-	lzms_init_range_encoder(&ctx->delta_match_range_encoder,
-				&ctx->rc, LZMS_NUM_DELTA_MATCH_STATES);
+	lzms_init_range_encoder(&c->delta_match_range_encoder,
+				&c->rc, LZMS_NUM_DELTA_MATCH_STATES);
 
-	for (size_t i = 0; i < ARRAY_LEN(ctx->delta_repeat_match_range_encoders); i++)
-		lzms_init_range_encoder(&ctx->delta_repeat_match_range_encoders[i],
-					&ctx->rc, LZMS_NUM_DELTA_REPEAT_MATCH_STATES);
+	for (unsigned i = 0; i < ARRAY_LEN(c->delta_repeat_match_range_encoders); i++)
+		lzms_init_range_encoder(&c->delta_repeat_match_range_encoders[i],
+					&c->rc, LZMS_NUM_DELTA_REPEAT_MATCH_STATES);
 
-	/* Initialize LRU match information.  */
-	lzms_init_lru_queues(&ctx->lru);
+	/* Set initial length costs for lengths < LZMS_NUM_FAST_LENGTHS.  */
+	lzms_update_fast_length_costs(c);
 }
 
 /* Flush the output streams, prepare the final compressed data, and return its
@@ -1263,65 +1331,77 @@ lzms_init_compressor(struct lzms_compressor *ctx, const u8 *udata, u32 ulen,
  * A return value of 0 indicates that the data could not be compressed to fit in
  * the available space.  */
 static size_t
-lzms_finalize(struct lzms_compressor *ctx, u8 *cdata, size_t csize_avail)
+lzms_finalize(struct lzms_compressor *c, u8 *cdata, size_t csize_avail)
 {
 	size_t num_forwards_bytes;
 	size_t num_backwards_bytes;
-	size_t compressed_size;
 
 	/* Flush both the forwards and backwards streams, and make sure they
 	 * didn't cross each other and start overwriting each other's data.  */
-	if (!lzms_output_bitstream_flush(&ctx->os)) {
-		LZMS_DEBUG("Backwards bitstream overrun.");
+	if (!lzms_output_bitstream_flush(&c->os))
 		return 0;
-	}
 
-	if (!lzms_range_encoder_raw_flush(&ctx->rc)) {
-		LZMS_DEBUG("Forwards bitstream overrun.");
+	if (!lzms_range_encoder_raw_flush(&c->rc))
 		return 0;
-	}
 
-	if (ctx->rc.out > ctx->os.out) {
-		LZMS_DEBUG("Two bitstreams crossed.");
+	if (c->rc.next > c->os.next)
 		return 0;
-	}
 
 	/* Now the compressed buffer contains the data output by the forwards
 	 * bitstream, then empty space, then data output by the backwards
 	 * bitstream.  Move the data output by the backwards bitstream to be
 	 * adjacent to the data output by the forward bitstream, and calculate
 	 * the compressed size that this results in.  */
-	num_forwards_bytes = (u8*)ctx->rc.out - (u8*)cdata;
-	num_backwards_bytes = ((u8*)cdata + csize_avail) - (u8*)ctx->os.out;
+	num_forwards_bytes = (u8*)c->rc.next - (u8*)cdata;
+	num_backwards_bytes = ((u8*)cdata + csize_avail) - (u8*)c->os.next;
 
-	memmove(cdata + num_forwards_bytes, ctx->os.out, num_backwards_bytes);
+	memmove(cdata + num_forwards_bytes, c->os.next, num_backwards_bytes);
 
-	compressed_size = num_forwards_bytes + num_backwards_bytes;
-	LZMS_DEBUG("num_forwards_bytes=%zu, num_backwards_bytes=%zu, "
-		   "compressed_size=%zu",
-		   num_forwards_bytes, num_backwards_bytes, compressed_size);
-	LZMS_ASSERT(compressed_size % 2 == 0);
-	return compressed_size;
+	return num_forwards_bytes + num_backwards_bytes;
 }
 
-
+/* Set internal compression parameters for the specified compression level and
+ * maximum window size.  */
 static void
 lzms_build_params(unsigned int compression_level,
-		  struct lzms_compressor_params *lzms_params)
+		  struct lzms_compressor_params *params)
 {
-	lzms_params->min_match_length  = (compression_level >= 50) ? 2 : 3;
-	lzms_params->nice_match_length = ((u64)compression_level * 32) / 50;
-	lzms_params->max_search_depth  = ((u64)compression_level * 50) / 50;
-	lzms_params->optim_array_length = 224 + compression_level * 16;
+	/* Allow length 2 matches if the compression level is sufficiently high.
+	 */
+	if (compression_level >= 45)
+		params->min_match_length = 2;
+	else
+		params->min_match_length = 3;
+
+	/* Scale nice_match_length and max_search_depth with the compression
+	 * level.  But to allow an optimization on length cost calculations,
+	 * don't allow nice_match_length to exceed LZMS_NUM_FAST_LENGTH.  */
+	params->nice_match_length = ((u64)compression_level * 32) / 50;
+	if (params->nice_match_length < params->min_match_length)
+		params->nice_match_length = params->min_match_length;
+	if (params->nice_match_length > LZMS_NUM_FAST_LENGTHS)
+		params->nice_match_length = LZMS_NUM_FAST_LENGTHS;
+	params->max_search_depth = compression_level;
+
+	params->optim_array_length = 1024;
 }
 
+/* Given the internal compression parameters and maximum window size, build the
+ * Lempel-Ziv match-finder parameters.  */
 static void
 lzms_build_mf_params(const struct lzms_compressor_params *lzms_params,
 		     u32 max_window_size, struct lz_mf_params *mf_params)
 {
 	memset(mf_params, 0, sizeof(*mf_params));
 
-	mf_params->algorithm = LZ_MF_DEFAULT;
+	/* Choose an appropriate match-finding algorithm.  */
+	if (max_window_size <= 2097152)
+		mf_params->algorithm = LZ_MF_BINARY_TREES;
+	else if (max_window_size <= 33554432)
+		mf_params->algorithm = LZ_MF_LCP_INTERVAL_TREE;
+	else
+		mf_params->algorithm = LZ_MF_LINKED_SUFFIX_ARRAY;
+
 	mf_params->max_window_size = max_window_size;
 	mf_params->min_match_len = lzms_params->min_match_length;
 	mf_params->max_search_depth = lzms_params->max_search_depth;
@@ -1329,21 +1409,34 @@ lzms_build_mf_params(const struct lzms_compressor_params *lzms_params,
 }
 
 static void
-lzms_free_compressor(void *_ctx);
+lzms_free_compressor(void *_c);
 
 static u64
 lzms_get_needed_memory(size_t max_block_size, unsigned int compression_level)
 {
 	struct lzms_compressor_params params;
+	struct lz_mf_params mf_params;
+	u64 size = 0;
 
-	lzms_build_params(compression_level, &params);
+	if (max_block_size >= INT32_MAX)
+		return 0;
 
-	u64 size = 0;
+	lzms_build_params(compression_level, &params);
+	lzms_build_mf_params(&params, max_block_size, &mf_params);
 
 	size += sizeof(struct lzms_compressor);
+
+	/* cur_window */
 	size += max_block_size;
-	size += lz_mf_get_needed_memory(LZ_MF_DEFAULT, max_block_size);
-	size += params.max_search_depth * sizeof(struct lz_match);
+
+	/* mf */
+	size += lz_mf_get_needed_memory(mf_params.algorithm, max_block_size);
+
+	/* matches */
+	size += min(params.max_search_depth, params.nice_match_length) *
+		sizeof(struct lz_match);
+
+	/* optimum */
 	size += (params.optim_array_length + params.nice_match_length) *
 		sizeof(struct lzms_mc_pos_data);
 
@@ -1354,7 +1447,7 @@ static int
 lzms_create_compressor(size_t max_block_size, unsigned int compression_level,
 		       void **ctx_ret)
 {
-	struct lzms_compressor *ctx;
+	struct lzms_compressor *c;
 	struct lzms_compressor_params params;
 	struct lz_mf_params mf_params;
 
@@ -1366,60 +1459,56 @@ lzms_create_compressor(size_t max_block_size, unsigned int compression_level,
 	if (!lz_mf_params_valid(&mf_params))
 		return WIMLIB_ERR_INVALID_PARAM;
 
-	ctx = CALLOC(1, sizeof(struct lzms_compressor));
-	if (!ctx)
+	c = CALLOC(1, sizeof(struct lzms_compressor));
+	if (!c)
 		goto oom;
 
-	ctx->params = params;
-	ctx->max_block_size = max_block_size;
+	c->params = params;
 
-	ctx->window = MALLOC(max_block_size);
-	if (!ctx->window)
+	c->cur_window = MALLOC(max_block_size);
+	if (!c->cur_window)
 		goto oom;
 
-	ctx->mf = lz_mf_alloc(&mf_params);
-	if (!ctx->mf)
+	c->mf = lz_mf_alloc(&mf_params);
+	if (!c->mf)
 		goto oom;
 
-	ctx->matches = MALLOC(params.max_search_depth * sizeof(struct lz_match));
-	if (!ctx->matches)
+	c->matches = MALLOC(min(params.max_search_depth,
+				params.nice_match_length) *
+			    sizeof(struct lz_match));
+	if (!c->matches)
 		goto oom;
 
-	ctx->optimum = MALLOC((params.optim_array_length +
-			       params.nice_match_length) *
-				sizeof(struct lzms_mc_pos_data));
-	if (!ctx->optimum)
+	c->optimum = MALLOC((params.optim_array_length +
+			     params.nice_match_length) *
+			    sizeof(struct lzms_mc_pos_data));
+	if (!c->optimum)
 		goto oom;
+	c->optimum_end = &c->optimum[params.optim_array_length];
 
-	/* Initialize position and length slot data if not done already.  */
 	lzms_init_slots();
 
-	/* Initialize range encoding cost table if not done already.  */
 	lzms_init_rc_costs();
 
-	*ctx_ret = ctx;
+	lzms_init_fast_slots(c);
+
+	*ctx_ret = c;
 	return 0;
 
 oom:
-	lzms_free_compressor(ctx);
+	lzms_free_compressor(c);
 	return WIMLIB_ERR_NOMEM;
 }
 
 static size_t
 lzms_compress(const void *uncompressed_data, size_t uncompressed_size,
-	      void *compressed_data, size_t compressed_size_avail, void *_ctx)
+	      void *compressed_data, size_t compressed_size_avail, void *_c)
 {
-	struct lzms_compressor *ctx = _ctx;
-	size_t compressed_size;
-
-	LZMS_DEBUG("uncompressed_size=%zu, compressed_size_avail=%zu",
-		   uncompressed_size, compressed_size_avail);
+	struct lzms_compressor *c = _c;
 
 	/* Don't bother compressing extremely small inputs.  */
-	if (uncompressed_size < 4) {
-		LZMS_DEBUG("Input too small to bother compressing.");
+	if (uncompressed_size < 4)
 		return 0;
-	}
 
 	/* Cap the available compressed size to a 32-bit integer and round it
 	 * down to the nearest multiple of 2.  */
@@ -1429,43 +1518,35 @@ lzms_compress(const void *uncompressed_data, size_t uncompressed_size,
 		compressed_size_avail--;
 
 	/* Initialize the compressor structures.  */
-	lzms_init_compressor(ctx, uncompressed_data, uncompressed_size,
-			     compressed_data, compressed_size_avail / 2);
+	lzms_prepare_compressor(c, uncompressed_data, uncompressed_size,
+				compressed_data, compressed_size_avail / 2);
 
 	/* Preprocess the uncompressed data.  */
-	lzms_x86_filter(ctx->window, ctx->window_size,
-			ctx->last_target_usages, false);
+	lzms_x86_filter(c->cur_window, c->cur_window_size,
+			c->last_target_usages, false);
+
+	/* Load the window into the match-finder.  */
+	lz_mf_load_window(c->mf, c->cur_window, c->cur_window_size);
 
 	/* Compute and encode a literal/match sequence that decompresses to the
 	 * preprocessed data.  */
-	lzms_encode(ctx);
-
-	/* Get and return the compressed data size.  */
-	compressed_size = lzms_finalize(ctx, compressed_data,
-					compressed_size_avail);
-
-	if (compressed_size == 0) {
-		LZMS_DEBUG("Data did not compress to requested size or less.");
-		return 0;
-	}
-
-	LZMS_DEBUG("Compressed %zu => %zu bytes",
-		   uncompressed_size, compressed_size);
+	lzms_near_optimal_parse(c);
 
-	return compressed_size;
+	/* Return the compressed data size or 0.  */
+	return lzms_finalize(c, compressed_data, compressed_size_avail);
 }
 
 static void
-lzms_free_compressor(void *_ctx)
+lzms_free_compressor(void *_c)
 {
-	struct lzms_compressor *ctx = _ctx;
-
-	if (ctx) {
-		FREE(ctx->window);
-		lz_mf_free(ctx->mf);
-		FREE(ctx->matches);
-		FREE(ctx->optimum);
-		FREE(ctx);
+	struct lzms_compressor *c = _c;
+
+	if (c) {
+		FREE(c->cur_window);
+		lz_mf_free(c->mf);
+		FREE(c->matches);
+		FREE(c->optimum);
+		FREE(c);
 	}
 }