From: Eric Biggers Date: Sun, 17 Aug 2014 04:11:20 +0000 (-0500) Subject: LZX, XPRESS: Use optimized write_bits() functions X-Git-Tag: v1.7.2~69 X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=4dae2eef895b95d1c2bc1bf5fc17413af8cc7952 LZX, XPRESS: Use optimized write_bits() functions For LZX, no handling of literal bytes is needed. Also, no padding at the end is needed; omitting it improves the compression ratio slightly. For XPRESS, no handling of bit counts > 16 is needed. --- diff --git a/include/wimlib/compiler.h b/include/wimlib/compiler.h index 567f07d0..221df688 100644 --- a/include/wimlib/compiler.h +++ b/include/wimlib/compiler.h @@ -15,6 +15,7 @@ # define WIMLIBAPI __attribute__((visibility("default"))) # endif # define _always_inline_attribute inline __attribute__((always_inline)) +# define _no_inline_attribute __attribute__((noinline)) # define _packed_attribute __attribute__((packed)) # define _format_attribute(type, format_str, args_start) \ /*__attribute__((format(type, format_str, args_start))) */ @@ -34,6 +35,7 @@ #else # define WIMLIBAPI # define _always_inline_attribute inline +# define _no_inline_attribute # define _format_attribute(type, format_str, args_start) # define _cold_attribute # define _packed_attribute diff --git a/include/wimlib/compress_common.h b/include/wimlib/compress_common.h index 9910d412..7913a138 100644 --- a/include/wimlib/compress_common.h +++ b/include/wimlib/compress_common.h @@ -2,9 +2,6 @@ * compress_common.h * * Header for compression code shared by multiple compression formats. - * - * The author dedicates this file to the public domain. - * You can do whatever you want with this file. */ #ifndef _WIMLIB_COMPRESS_COMMON_H @@ -12,55 +9,6 @@ #include "wimlib/types.h" -/* Structure to keep track of the current state sending bits and bytes to the - * compressed output buffer. */ -struct output_bitstream { - - /* Variable that holds up to 16 bits that haven't yet been flushed to - * the output. */ - u16 bitbuf; - - /* Number of free bits in @bitbuf; that is, 16 minus the number of valid - * bits in @bitbuf. */ - unsigned free_bits; - - /* Pointer to the start of the output buffer. */ - u8 *output_start; - - /* Position at which to write the next 16 bits. */ - u8 *bit_output; - - /* Next position to write 16 bits, after they are written to bit_output. - * This is after @next_bit_output and may be separated from @bit_output - * by literal bytes. */ - u8 *next_bit_output; - - /* Next position to write literal bytes. This is after @bit_output and - * @next_bit_output, and may be separated from them by literal bytes. - */ - u8 *output; - - /* Number of bytes remaining in the @output buffer. */ - u32 bytes_remaining; - - /* Set to true if the buffer has been exhausted. */ - bool overrun; -}; - -extern void -init_output_bitstream(struct output_bitstream *ostream, - void *data, unsigned num_bytes); - -extern u32 -flush_output_bitstream(struct output_bitstream *ostream); - -extern void -bitstream_put_bits(struct output_bitstream *ostream, - u32 bits, unsigned num_bits); - -extern void -bitstream_put_byte(struct output_bitstream *ostream, u8 n); - extern void make_canonical_huffman_code(unsigned num_syms, unsigned max_codeword_len, diff --git a/include/wimlib/lzx.h b/include/wimlib/lzx.h index 576d8bd5..67fb3561 100644 --- a/include/wimlib/lzx.h +++ b/include/wimlib/lzx.h @@ -15,10 +15,8 @@ //#define ENABLE_LZX_DEBUG #ifdef ENABLE_LZX_DEBUG -# define LZX_DEBUG DEBUG # define LZX_ASSERT wimlib_assert #else -# define LZX_DEBUG(format, ...) # define LZX_ASSERT(...) #endif diff --git a/src/compress_common.c b/src/compress_common.c index 1653b04f..130bfc11 100644 --- a/src/compress_common.c +++ b/src/compress_common.c @@ -15,103 +15,11 @@ #endif #include "wimlib/assert.h" -#include "wimlib/endianness.h" -#include "wimlib/compiler.h" #include "wimlib/compress_common.h" #include "wimlib/util.h" #include -/* Writes @num_bits bits, given by the @num_bits least significant bits of - * @bits, to the output @ostream. */ -void -bitstream_put_bits(struct output_bitstream *ostream, u32 bits, - unsigned num_bits) -{ - bits &= (1U << num_bits) - 1; - while (num_bits > ostream->free_bits) { - /* Buffer variable does not have space for the new bits. It - * needs to be flushed as a 16-bit integer. Bits in the second - * byte logically precede those in the first byte - * (little-endian), but within each byte the bits are ordered - * from high to low. This is true for both XPRESS and LZX - * compression. */ - - /* There must be at least 2 bytes of space remaining. */ - if (unlikely(ostream->bytes_remaining < 2)) { - ostream->overrun = true; - return; - } - - /* Fill the buffer with as many bits that fit. */ - unsigned fill_bits = ostream->free_bits; - - ostream->bitbuf <<= fill_bits; - ostream->bitbuf |= bits >> (num_bits - fill_bits); - - *(le16*)ostream->bit_output = cpu_to_le16(ostream->bitbuf); - ostream->bit_output = ostream->next_bit_output; - ostream->next_bit_output = ostream->output; - ostream->output += 2; - ostream->bytes_remaining -= 2; - - ostream->free_bits = 16; - num_bits -= fill_bits; - bits &= (1U << num_bits) - 1; - } - - /* Buffer variable has space for the new bits. */ - ostream->bitbuf = (ostream->bitbuf << num_bits) | bits; - ostream->free_bits -= num_bits; -} - -void -bitstream_put_byte(struct output_bitstream *ostream, u8 n) -{ - if (unlikely(ostream->bytes_remaining < 1)) { - ostream->overrun = true; - return; - } - *ostream->output++ = n; - ostream->bytes_remaining--; -} - -/* Flushes any remaining bits to the output bitstream. - * - * Returns -1 if the stream has overrun; otherwise returns the total number of - * bytes in the output. */ -u32 -flush_output_bitstream(struct output_bitstream *ostream) -{ - if (unlikely(ostream->overrun)) - return (u32)~0UL; - - *(le16*)ostream->bit_output = - cpu_to_le16((u16)((u32)ostream->bitbuf << ostream->free_bits)); - *(le16*)ostream->next_bit_output = - cpu_to_le16(0); - - return ostream->output - ostream->output_start; -} - -/* Initializes an output bit buffer to write its output to the memory location - * pointer to by @data. */ -void -init_output_bitstream(struct output_bitstream *ostream, - void *data, unsigned num_bytes) -{ - wimlib_assert(num_bytes >= 4); - - ostream->bitbuf = 0; - ostream->free_bits = 16; - ostream->output_start = data; - ostream->bit_output = data; - ostream->next_bit_output = data + 2; - ostream->output = data + 4; - ostream->bytes_remaining = num_bytes - 4; - ostream->overrun = false; -} - /* Given the binary tree node A[subtree_idx] whose children already * satisfy the maxheap property, swap the node with its greater child * until it is greater than both its children, so that the maxheap diff --git a/src/lzx-compress.c b/src/lzx-compress.c index 7e811e4e..0a4edb0e 100644 --- a/src/lzx-compress.c +++ b/src/lzx-compress.c @@ -196,6 +196,7 @@ #include "wimlib/compressor_ops.h" #include "wimlib/compress_common.h" +#include "wimlib/endianness.h" #include "wimlib/error.h" #include "wimlib/lz_mf.h" #include "wimlib/lzx.h" @@ -455,6 +456,129 @@ struct lzx_mc_pos_data { struct lzx_lru_queue queue; }; + +/* + * Structure to keep track of the current state of sending bits to the + * compressed output buffer. + * + * The LZX bitstream is encoded as a sequence of 16-bit coding units. + */ +struct lzx_output_bitstream { + + /* Bits that haven't yet been written to the output buffer. */ + u32 bitbuf; + + /* Number of bits currently held in @bitbuf. */ + u32 bitcount; + + /* Pointer to the start of the output buffer. */ + le16 *start; + + /* Pointer to the position in the output buffer at which the next coding + * unit should be written. */ + le16 *next; + + /* Pointer past the end of the output buffer. */ + le16 *end; +}; + +/* + * Initialize the output bitstream. + * + * @os + * The output bitstream structure to initialize. + * @buffer + * The buffer being written to. + * @size + * Size of @buffer, in bytes. + */ +static void +lzx_init_output(struct lzx_output_bitstream *os, void *buffer, u32 size) +{ + os->bitbuf = 0; + os->bitcount = 0; + os->start = buffer; + os->next = os->start; + os->end = os->start + size / sizeof(le16); +} + +/* + * Write some bits to the output bitstream. + * + * The bits are given by the low-order @num_bits bits of @bits. Higher-order + * bits in @bits cannot be set. At most 17 bits can be written at once. + * + * @max_bits is a compile-time constant that specifies the maximum number of + * bits that can ever be written at the call site. Currently, it is used to + * optimize away the conditional code for writing a second 16-bit coding unit + * when writing fewer than 17 bits. + * + * If the output buffer space is exhausted, then the bits will be ignored, and + * lzx_flush_output() will return 0 when it gets called. + */ +static _always_inline_attribute void +lzx_write_varbits(struct lzx_output_bitstream *os, + const u32 bits, const unsigned int num_bits, + const unsigned int max_num_bits) +{ + /* This code is optimized for LZX, which never needs to write more than + * 17 bits at once. */ + LZX_ASSERT(num_bits <= 17); + LZX_ASSERT(num_bits <= max_num_bits); + LZX_ASSERT(os->bitcount <= 15); + + /* Add the bits to the bit buffer variable. @bitcount will be at most + * 15, so there will be just enough space for the maximum possible + * @num_bits of 17. */ + os->bitcount += num_bits; + os->bitbuf = (os->bitbuf << num_bits) | bits; + + /* Check whether any coding units need to be written. */ + if (os->bitcount >= 16) { + + os->bitcount -= 16; + + /* Write a coding unit, unless it would overflow the buffer. */ + if (os->next != os->end) + *os->next++ = cpu_to_le16(os->bitbuf >> os->bitcount); + + /* If writing 17 bits, a second coding unit might need to be + * written. But because 'max_num_bits' is a compile-time + * constant, the compiler will optimize away this code at most + * call sites. */ + if (max_num_bits == 17 && os->bitcount == 16) { + if (os->next != os->end) + *os->next++ = cpu_to_le16(os->bitbuf); + os->bitcount = 0; + } + } +} + +/* Use when @num_bits is a compile-time constant. Otherwise use + * lzx_write_varbits(). */ +static _always_inline_attribute void +lzx_write_bits(struct lzx_output_bitstream *os, + const u32 bits, const unsigned int num_bits) +{ + lzx_write_varbits(os, bits, num_bits, num_bits); +} + +/* + * Flush the last coding unit to the output buffer if needed. Return the total + * number of bytes written to the output buffer, or 0 if an overflow occurred. + */ +static u32 +lzx_flush_output(struct lzx_output_bitstream *os) +{ + if (os->next == os->end) + return 0; + + if (os->bitcount != 0) + *os->next++ = cpu_to_le16(os->bitbuf << (16 - os->bitcount)); + + return (const u8 *)os->next - (const u8 *)os->start; +} + /* Returns the LZX position slot that corresponds to a given match offset, * taking into account the recent offset queue and updating it if the offset is * found in it. */ @@ -522,7 +646,7 @@ lzx_make_huffman_codes(const struct lzx_freqs *freqs, /* * Output a precomputed LZX match. * - * @out: + * @os: * The bitstream to which to write the match. * @block_type: * The type of the LZX block (LZX_BLOCKTYPE_ALIGNED or @@ -534,30 +658,23 @@ lzx_make_huffman_codes(const struct lzx_freqs *freqs, * and aligned offset Huffman codes for the current LZX compressed block. */ static void -lzx_write_match(struct output_bitstream *out, int block_type, +lzx_write_match(struct lzx_output_bitstream *os, int block_type, struct lzx_item match, const struct lzx_codes *codes) { - /* low 8 bits are the match length minus 2 */ unsigned match_len_minus_2 = match.data & 0xff; - /* Next 17 bits are the position footer */ - unsigned position_footer = (match.data >> 8) & 0x1ffff; /* 17 bits */ - /* Next 6 bits are the position slot. */ - unsigned position_slot = (match.data >> 25) & 0x3f; /* 6 bits */ + u32 position_footer = (match.data >> 8) & 0x1ffff; + unsigned position_slot = (match.data >> 25) & 0x3f; unsigned len_header; unsigned len_footer; unsigned main_symbol; unsigned num_extra_bits; - unsigned verbatim_bits; - unsigned aligned_bits; /* If the match length is less than MIN_MATCH_LEN (= 2) + - * NUM_PRIMARY_LENS (= 7), the length header contains - * the match length minus MIN_MATCH_LEN, and there is no - * length footer. + * NUM_PRIMARY_LENS (= 7), the length header contains the match length + * minus MIN_MATCH_LEN, and there is no length footer. * - * Otherwise, the length header contains - * NUM_PRIMARY_LENS, and the length footer contains - * the match length minus NUM_PRIMARY_LENS minus + * Otherwise, the length header contains NUM_PRIMARY_LENS, and the + * length footer contains the match length minus NUM_PRIMARY_LENS minus * MIN_MATCH_LEN. */ if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) { len_header = match_len_minus_2; @@ -575,46 +692,49 @@ lzx_write_match(struct output_bitstream *out, int block_type, main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS; /* Output main symbol. */ - bitstream_put_bits(out, codes->codewords.main[main_symbol], - codes->lens.main[main_symbol]); + lzx_write_varbits(os, codes->codewords.main[main_symbol], + codes->lens.main[main_symbol], + LZX_MAX_MAIN_CODEWORD_LEN); /* If there is a length footer, output it using the * length Huffman code. */ - if (len_header == LZX_NUM_PRIMARY_LENS) - bitstream_put_bits(out, codes->codewords.len[len_footer], - codes->lens.len[len_footer]); + if (len_header == LZX_NUM_PRIMARY_LENS) { + lzx_write_varbits(os, codes->codewords.len[len_footer], + codes->lens.len[len_footer], + LZX_MAX_LEN_CODEWORD_LEN); + } + + /* Output the position footer. */ num_extra_bits = lzx_get_num_extra_bits(position_slot); - /* For aligned offset blocks with at least 3 extra bits, output the - * verbatim bits literally, then the aligned bits encoded using the - * aligned offset code. Otherwise, only the verbatim bits need to be - * output. */ if ((block_type == LZX_BLOCKTYPE_ALIGNED) && (num_extra_bits >= 3)) { - verbatim_bits = position_footer >> 3; - bitstream_put_bits(out, verbatim_bits, - num_extra_bits - 3); + /* Aligned offset blocks: The low 3 bits of the position footer + * are Huffman-encoded using the aligned offset code. The + * remaining bits are output literally. */ + + lzx_write_varbits(os, + position_footer >> 3, num_extra_bits - 3, 14); - aligned_bits = (position_footer & 7); - bitstream_put_bits(out, - codes->codewords.aligned[aligned_bits], - codes->lens.aligned[aligned_bits]); + lzx_write_varbits(os, + codes->codewords.aligned[position_footer & 7], + codes->lens.aligned[position_footer & 7], + LZX_MAX_ALIGNED_CODEWORD_LEN); } else { - /* verbatim bits is the same as the position - * footer, in this case. */ - bitstream_put_bits(out, position_footer, num_extra_bits); + /* Verbatim blocks, or fewer than 3 extra bits: All position + * footer bits are output literally. */ + lzx_write_varbits(os, position_footer, num_extra_bits, 17); } } /* Output an LZX literal (encoded with the main Huffman code). */ static void -lzx_write_literal(struct output_bitstream *out, u8 literal, +lzx_write_literal(struct lzx_output_bitstream *os, unsigned literal, const struct lzx_codes *codes) { - bitstream_put_bits(out, - codes->codewords.main[literal], - codes->lens.main[literal]); + lzx_write_varbits(os, codes->codewords.main[literal], + codes->lens.main[literal], LZX_MAX_MAIN_CODEWORD_LEN); } static unsigned @@ -774,7 +894,7 @@ lzx_build_precode(const u8 lens[restrict], * as deltas from the codeword lengths of the corresponding code in the previous * block. * - * @out: + * @os: * Bitstream to which to write the compressed Huffman code. * @lens: * The codeword lengths, indexed by symbol, in the Huffman code. @@ -785,7 +905,7 @@ lzx_build_precode(const u8 lens[restrict], * The number of symbols in the Huffman code. */ static void -lzx_write_compressed_code(struct output_bitstream *out, +lzx_write_compressed_code(struct lzx_output_bitstream *os, const u8 lens[restrict], const u8 prev_lens[restrict], unsigned num_syms) @@ -810,28 +930,28 @@ lzx_write_compressed_code(struct output_bitstream *out, /* Write the lengths of the precode codes to the output. */ for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) - bitstream_put_bits(out, precode_lens[i], - LZX_PRECODE_ELEMENT_SIZE); + lzx_write_bits(os, precode_lens[i], LZX_PRECODE_ELEMENT_SIZE); /* Write the length symbols, encoded with the precode, to the output. */ for (i = 0; i < num_output_syms; ) { precode_sym = output_syms[i++]; - bitstream_put_bits(out, precode_codewords[precode_sym], - precode_lens[precode_sym]); + lzx_write_varbits(os, precode_codewords[precode_sym], + precode_lens[precode_sym], + LZX_MAX_PRE_CODEWORD_LEN); switch (precode_sym) { case 17: - bitstream_put_bits(out, output_syms[i++], 4); + lzx_write_bits(os, output_syms[i++], 4); break; case 18: - bitstream_put_bits(out, output_syms[i++], 5); + lzx_write_bits(os, output_syms[i++], 5); break; case 19: - bitstream_put_bits(out, output_syms[i++], 1); - bitstream_put_bits(out, - precode_codewords[output_syms[i]], - precode_lens[output_syms[i]]); + lzx_write_bits(os, output_syms[i++], 1); + lzx_write_varbits(os, precode_codewords[output_syms[i]], + precode_lens[output_syms[i]], + LZX_MAX_PRE_CODEWORD_LEN); i++; break; default: @@ -845,7 +965,7 @@ lzx_write_compressed_code(struct output_bitstream *out, * compressed block to the output bitstream in the final compressed * representation. * - * @ostream + * @os * The output bitstream. * @block_type * The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or @@ -859,7 +979,7 @@ lzx_write_compressed_code(struct output_bitstream *out, * LZX compressed block. */ static void -lzx_write_items(struct output_bitstream *ostream, int block_type, +lzx_write_items(struct lzx_output_bitstream *os, int block_type, const struct lzx_item items[], u32 num_items, const struct lzx_codes *codes) { @@ -868,32 +988,30 @@ lzx_write_items(struct output_bitstream *ostream, int block_type, * indicates whether the item is an actual LZ-style match (1) or * a literal byte (0). */ if (items[i].data & 0x80000000) - lzx_write_match(ostream, block_type, items[i], codes); + lzx_write_match(os, block_type, items[i], codes); else - lzx_write_literal(ostream, items[i].data, codes); + lzx_write_literal(os, items[i].data, codes); } } /* Write an LZX aligned offset or verbatim block to the output. */ static void lzx_write_compressed_block(int block_type, - unsigned block_size, - unsigned max_window_size, + u32 block_size, + u32 max_window_size, unsigned num_main_syms, struct lzx_item * chosen_items, - unsigned num_chosen_items, + u32 num_chosen_items, const struct lzx_codes * codes, const struct lzx_codes * prev_codes, - struct output_bitstream * ostream) + struct lzx_output_bitstream * os) { - unsigned i; - LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED || block_type == LZX_BLOCKTYPE_VERBATIM); /* The first three bits indicate the type of block and are one of the * LZX_BLOCKTYPE_* constants. */ - bitstream_put_bits(ostream, block_type, 3); + lzx_write_bits(os, block_type, 3); /* Output the block size. * @@ -911,64 +1029,50 @@ lzx_write_compressed_block(int block_type, * because WIMs created with chunk size greater than 32768 can seemingly * only be opened by wimlib anyway. */ if (block_size == LZX_DEFAULT_BLOCK_SIZE) { - bitstream_put_bits(ostream, 1, 1); + lzx_write_bits(os, 1, 1); } else { - bitstream_put_bits(ostream, 0, 1); + lzx_write_bits(os, 0, 1); if (max_window_size >= 65536) - bitstream_put_bits(ostream, block_size >> 16, 8); + lzx_write_bits(os, block_size >> 16, 8); - bitstream_put_bits(ostream, block_size, 16); + lzx_write_bits(os, block_size & 0xFFFF, 16); } - /* Write out lengths of the main code. Note that the LZX specification - * incorrectly states that the aligned offset code comes after the - * length code, but in fact it is the very first code to be written - * (before the main code). */ - if (block_type == LZX_BLOCKTYPE_ALIGNED) - for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) - bitstream_put_bits(ostream, codes->lens.aligned[i], - LZX_ALIGNEDCODE_ELEMENT_SIZE); - - /* Write the precode and lengths for the first LZX_NUM_CHARS symbols in - * the main code, which are the codewords for literal bytes. */ - lzx_write_compressed_code(ostream, - codes->lens.main, + /* Output the aligned offset code. */ + if (block_type == LZX_BLOCKTYPE_ALIGNED) { + for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) { + lzx_write_bits(os, codes->lens.aligned[i], + LZX_ALIGNEDCODE_ELEMENT_SIZE); + } + } + + /* Output the main code (two parts). */ + lzx_write_compressed_code(os, codes->lens.main, prev_codes->lens.main, LZX_NUM_CHARS); - - /* Write the precode and lengths for the rest of the main code, which - * are the codewords for match headers. */ - lzx_write_compressed_code(ostream, - codes->lens.main + LZX_NUM_CHARS, + lzx_write_compressed_code(os, codes->lens.main + LZX_NUM_CHARS, prev_codes->lens.main + LZX_NUM_CHARS, num_main_syms - LZX_NUM_CHARS); - /* Write the precode and lengths for the length code. */ - lzx_write_compressed_code(ostream, - codes->lens.len, + /* Output the length code. */ + lzx_write_compressed_code(os, codes->lens.len, prev_codes->lens.len, LZX_LENCODE_NUM_SYMBOLS); - /* Write the actual matches and literals. */ - lzx_write_items(ostream, block_type, - chosen_items, num_chosen_items, codes); + /* Output the compressed matches and literals. */ + lzx_write_items(os, block_type, chosen_items, num_chosen_items, codes); } /* Write out the LZX blocks that were computed. */ static void -lzx_write_all_blocks(struct lzx_compressor *c, struct output_bitstream *ostream) +lzx_write_all_blocks(struct lzx_compressor *c, struct lzx_output_bitstream *os) { const struct lzx_codes *prev_codes = &c->zero_codes; for (unsigned i = 0; i < c->num_blocks; i++) { const struct lzx_block_spec *spec = &c->block_specs[i]; - LZX_DEBUG("Writing block %u/%u (type=%d, size=%u, num_chosen_items=%u)...", - i + 1, c->num_blocks, - spec->block_type, spec->block_size, - spec->num_chosen_items); - lzx_write_compressed_block(spec->block_type, spec->block_size, c->max_window_size, @@ -977,7 +1081,7 @@ lzx_write_all_blocks(struct lzx_compressor *c, struct output_bitstream *ostream) spec->num_chosen_items, &spec->codes, prev_codes, - ostream); + os); prev_codes = &spec->codes; } @@ -1001,7 +1105,7 @@ lzx_tally_match(unsigned match_len, u32 match_offset, struct lzx_freqs *freqs, struct lzx_lru_queue *queue) { unsigned position_slot; - unsigned position_footer; + u32 position_footer; u32 len_header; unsigned main_symbol; unsigned len_footer; @@ -1013,7 +1117,7 @@ lzx_tally_match(unsigned match_len, u32 match_offset, * as part of the main symbol) and a position footer. */ position_slot = lzx_get_position_slot(match_offset, queue); position_footer = (match_offset + LZX_OFFSET_OFFSET) & - ((1U << lzx_get_num_extra_bits(position_slot)) - 1); + (((u32)1 << lzx_get_num_extra_bits(position_slot)) - 1); /* The match length shall be encoded as a length header (itself encoded * as part of the main symbol) and an optional length footer. */ @@ -1964,7 +2068,7 @@ lzx_choose_items_for_block(struct lzx_compressor *c, struct lzx_block_spec *spec struct lz_match lz_match; struct lzx_item lzx_item; - LZX_ASSERT(num_passes >= 1); + LZX_ASSERT(num_passes_remaining >= 1); LZX_ASSERT(lz_mf_get_position(c->mf) == spec->window_pos); c->match_window_end = spec->window_pos + spec->block_size; @@ -2258,44 +2362,28 @@ lzx_compress(const void *uncompressed_data, size_t uncompressed_size, void *compressed_data, size_t compressed_size_avail, void *_c) { struct lzx_compressor *c = _c; - struct output_bitstream ostream; - size_t compressed_size; + struct lzx_output_bitstream os; - if (uncompressed_size < 100) { - LZX_DEBUG("Too small to bother compressing."); + /* Don't bother compressing very small inputs. */ + if (uncompressed_size < 100) return 0; - } - - LZX_DEBUG("Attempting to compress %zu bytes...", - uncompressed_size); /* The input data must be preprocessed. To avoid changing the original * input, copy it to a temporary buffer. */ memcpy(c->cur_window, uncompressed_data, uncompressed_size); c->cur_window_size = uncompressed_size; - /* Before doing any actual compression, do the call instruction (0xe8 - * byte) translation on the uncompressed data. */ + /* Preprocess the data. */ lzx_do_e8_preprocessing(c->cur_window, c->cur_window_size); /* Prepare the compressed data. */ lzx_prepare_blocks(c); - /* Generate the compressed data. */ - init_output_bitstream(&ostream, compressed_data, compressed_size_avail); - lzx_write_all_blocks(c, &ostream); - - compressed_size = flush_output_bitstream(&ostream); - if (compressed_size == (u32)~0UL) { - LZX_DEBUG("Data did not compress to %zu bytes or less!", - compressed_size_avail); - return 0; - } - - LZX_DEBUG("Done: compressed %zu => %zu bytes.", - uncompressed_size, compressed_size); - - return compressed_size; + /* Generate the compressed data and return its size, or 0 if an overflow + * occurred. */ + lzx_init_output(&os, compressed_data, compressed_size_avail); + lzx_write_all_blocks(c, &os); + return lzx_flush_output(&os); } static void diff --git a/src/xpress-compress.c b/src/xpress-compress.c index 14cf2fcc..e1884978 100644 --- a/src/xpress-compress.c +++ b/src/xpress-compress.c @@ -30,6 +30,7 @@ #include "wimlib/compressor_ops.h" #include "wimlib/compress_common.h" +#include "wimlib/endianness.h" #include "wimlib/error.h" #include "wimlib/lz_mf.h" #include "wimlib/util.h" @@ -128,9 +129,121 @@ struct xpress_item { /* For literals, offset == 0 and adjusted_len is the literal byte. */ }; +/* + * Structure to keep track of the current state of sending data to the + * compressed output buffer. + * + * The XPRESS bitstream is encoded as a sequence of little endian 16-bit coding + * units interwoven with literal bytes. + */ +struct xpress_output_bitstream { + + /* Bits that haven't yet been written to the output buffer. */ + u32 bitbuf; + + /* Number of bits currently held in @bitbuf. */ + u32 bitcount; + + /* Pointer to the start of the output buffer. */ + u8 *start; + + /* Pointer to the location in the ouput buffer at which to write the + * next 16 bits. */ + u8 *next_bits; + + /* Pointer to the location in the output buffer at which to write the + * next 16 bits, after @next_bits. */ + u8 *next_bits2; + + /* Pointer to the location in the output buffer at which to write the + * next literal byte. */ + u8 *next_byte; + + /* Pointer to the end of the output buffer. */ + u8 *end; +}; + +/* + * Initialize the output bitstream. + * + * @os + * The output bitstream structure to initialize. + * @buffer + * The buffer to write to. + * @size + * Size of @buffer, in bytes. Must be at least 4. + */ +static void +xpress_init_output(struct xpress_output_bitstream *os, void *buffer, u32 size) +{ + os->bitbuf = 0; + os->bitcount = 0; + os->start = buffer; + os->next_bits = os->start; + os->next_bits2 = os->start + 2; + os->next_byte = os->start + 4; + os->end = os->start + size; +} + +/* + * Write some bits to the output bitstream. + * + * The bits are given by the low-order @num_bits bits of @bits. Higher-order + * bits in @bits cannot be set. At most 16 bits can be written at once. + * + * If the output buffer space is exhausted, then the bits will be ignored, and + * xpress_flush_output() will return 0 when it gets called. + */ +static _always_inline_attribute void +xpress_write_bits(struct xpress_output_bitstream *os, + const u32 bits, const unsigned int num_bits) +{ + /* This code is optimized for XPRESS, which never needs to write more + * than 16 bits at once. */ + + os->bitcount += num_bits; + os->bitbuf = (os->bitbuf << num_bits) | bits; + + if (os->bitcount > 16) { + os->bitcount -= 16; + if (os->end - os->next_byte >= 2) { + *(le16 *)os->next_bits = cpu_to_le16(os->bitbuf >> os->bitcount); + os->next_bits = os->next_bits2; + os->next_bits2 = os->next_byte; + os->next_byte += 2; + } + } +} + +/* + * Interweave a literal byte into the output bitstream. + */ +static _always_inline_attribute void +xpress_write_byte(struct xpress_output_bitstream *os, u8 byte) +{ + if (os->next_byte < os->end) + *os->next_byte++ = byte; +} + +/* + * Flush the last coding unit to the output buffer if needed. Return the total + * number of bytes written to the output buffer, or 0 if an overflow occurred. + */ +static u32 +xpress_flush_output(struct xpress_output_bitstream *os) +{ + if (unlikely(os->end - os->next_byte < 2)) + return 0; + + *(le16 *)os->next_bits = cpu_to_le16(os->bitbuf << (16 - os->bitcount)); + *(le16 *)os->next_bits2 = cpu_to_le16(0); + + return os->next_byte - os->start; +} + /* Output an XPRESS match. */ static void -xpress_write_match(struct xpress_item match, struct output_bitstream *ostream, +xpress_write_match(struct xpress_item match, struct xpress_output_bitstream *os, const u32 codewords[], const u8 lens[]) { unsigned len_hdr = min(match.adjusted_len, 0xf); @@ -138,41 +251,41 @@ xpress_write_match(struct xpress_item match, struct output_bitstream *ostream, unsigned sym = XPRESS_NUM_CHARS + ((offset_bsr << 4) | len_hdr); /* Huffman symbol */ - bitstream_put_bits(ostream, codewords[sym], lens[sym]); + xpress_write_bits(os, codewords[sym], lens[sym]); /* If length >= 18, one extra length byte. * If length >= 273, three (total) extra length bytes. */ if (match.adjusted_len >= 0xf) { u8 byte1 = min(match.adjusted_len - 0xf, 0xff); - bitstream_put_byte(ostream, byte1); + xpress_write_byte(os, byte1); if (byte1 == 0xff) { - bitstream_put_byte(ostream, match.adjusted_len & 0xff); - bitstream_put_byte(ostream, match.adjusted_len >> 8); + xpress_write_byte(os, match.adjusted_len & 0xff); + xpress_write_byte(os, match.adjusted_len >> 8); } } /* Offset bits */ - bitstream_put_bits(ostream, match.offset ^ (1U << offset_bsr), offset_bsr); + xpress_write_bits(os, match.offset ^ (1U << offset_bsr), offset_bsr); } /* Output a sequence of XPRESS matches and literals. */ static void -xpress_write_items(struct output_bitstream *ostream, +xpress_write_items(struct xpress_output_bitstream *os, const struct xpress_item items[], u32 num_items, const u32 codewords[], const u8 lens[]) { for (u32 i = 0; i < num_items; i++) { if (items[i].offset) { /* Match */ - xpress_write_match(items[i], ostream, codewords, lens); + xpress_write_match(items[i], os, codewords, lens); } else { /* Literal */ unsigned lit = items[i].adjusted_len; - bitstream_put_bits(ostream, codewords[lit], lens[lit]); + xpress_write_bits(os, codewords[lit], lens[lit]); } } /* End-of-data symbol (required for MS compatibility) */ - bitstream_put_bits(ostream, codewords[XPRESS_END_OF_DATA], lens[XPRESS_END_OF_DATA]); + xpress_write_bits(os, codewords[XPRESS_END_OF_DATA], lens[XPRESS_END_OF_DATA]); } /* Make the Huffman code for XPRESS. @@ -1061,19 +1174,13 @@ xpress_compress(const void *uncompressed_data, size_t uncompressed_size, struct xpress_compressor *c = _c; u32 num_chosen_items; u8 *cptr; - struct output_bitstream ostream; + struct xpress_output_bitstream os; u32 compressed_size; /* XPRESS requires 256 bytes of overhead for the Huffman code, so it's * impossible to compress 256 bytes or less of data to less than the - * input size. - * - * +1 to take into account that the buffer for compressed data is 1 byte - * smaller than the buffer for uncompressed data. - * - * +4 to take into account that init_output_bitstream() requires at - * least 4 bytes of data. */ - if (compressed_size_avail < XPRESS_NUM_SYMBOLS / 2 + 1 + 4) + * input size. */ + if (compressed_size_avail < XPRESS_NUM_SYMBOLS / 2 + 50) return 0; /* Determine match/literal sequence to divide the data into. */ @@ -1087,14 +1194,14 @@ xpress_compress(const void *uncompressed_data, size_t uncompressed_size, *cptr++ = (c->lens[i] & 0xf) | (c->lens[i + 1] << 4); /* Output the encoded matches/literals. */ - init_output_bitstream(&ostream, cptr, - compressed_size_avail - XPRESS_NUM_SYMBOLS / 2 - 1); - xpress_write_items(&ostream, c->chosen_items, num_chosen_items, + xpress_init_output(&os, cptr, + compressed_size_avail - XPRESS_NUM_SYMBOLS / 2); + xpress_write_items(&os, c->chosen_items, num_chosen_items, c->codewords, c->lens); /* Flush any pending data and get the length of the compressed data. */ - compressed_size = flush_output_bitstream(&ostream); - if (compressed_size == (u32)~0UL) + compressed_size = xpress_flush_output(&os); + if (compressed_size == 0) return 0; /* Return the length of the compressed data. */