--- /dev/null
+/*
+ * decompress_common.c
+ *
+ * Code for decompression shared among multiple compression formats.
+ */
+
+/*
+ * Copyright (C) 2012, 2013 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.
+ *
+ * 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
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with wimlib; if not, see http://www.gnu.org/licenses/.
+ */
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include "wimlib/decompress_common.h"
+#include "wimlib/error.h"
+#include "wimlib/util.h"
+
+#include <string.h>
+
+#ifdef __GNUC__
+# ifdef __SSE2__
+# define USE_SSE2_FILL
+# include <emmintrin.h>
+# else
+# define USE_LONG_FILL
+# endif
+#endif
+
+/*
+ * make_huffman_decode_table: - Builds a fast huffman decoding table from an
+ * array that gives the length of the codeword for each symbol in the alphabet.
+ * Originally based on code written by David Tritscher (taken the original LZX
+ * decompression code); also heavily modified to add some optimizations used in
+ * the zlib code, as well as more comments; also added some optimizations to
+ * make filling in the decode table entries faster (may not help significantly
+ * though).
+ *
+ * @decode_table: The array in which to create the fast huffman decoding
+ * table. It must have a length of at least
+ * (2**table_bits) + 2 * num_syms to guarantee
+ * that there is enough space. Also must be 16-byte
+ * aligned (at least when USE_SSE2_FILL gets defined).
+ *
+ * @num_syms: Number of symbols in the alphabet, including symbols
+ * that do not appear in this particular input chunk.
+ *
+ * @table_bits: Any symbols with a code length of table_bits or less can
+ * be decoded in one lookup of the table. 2**table_bits
+ * must be greater than or equal to @num_syms if there are
+ * any Huffman codes longer than @table_bits.
+ *
+ * @lens: An array of length @num_syms, indexable by symbol, that
+ * gives the length of the Huffman codeword for that
+ * symbol. Because the Huffman tree is in canonical form,
+ * it can be reconstructed by only knowing the length of
+ * the codeword for each symbol. It is assumed, but not
+ * checked, that every length is less than
+ * @max_codeword_len.
+ *
+ * @max_codeword_len: The longest codeword length allowed in the compression
+ * format.
+ *
+ * Returns 0 on success; returns -1 if the length values do not correspond to a
+ * valid Huffman tree.
+ *
+ * The format of the Huffamn decoding table is as follows. The first (1 <<
+ * table_bits) entries of the table are indexed by chunks of the input of size
+ * @table_bits. If the next Huffman codeword in the input happens to have a
+ * length of exactly @table_bits, the symbol is simply read directly from the
+ * decoding table. Alternatively, if the next Huffman codeword has length _less
+ * than_ @table_bits, the symbol is also read directly from the decode table;
+ * this is possible because every entry in the table that is indexed by an
+ * integer that has the shorter codeword as a binary prefix is filled in with
+ * the appropriate symbol. If a codeword has length n <= table_bits, it will
+ * have 2**(table_bits - n) possible suffixes, and thus that many entries in the
+ * decoding table.
+ *
+ * It's a bit more complicated if the next Huffman codeword has length of more
+ * than @table_bits. The table entry indexed by the first @table_bits of that
+ * codeword cannot give the appropriate symbol directly, because that entry is
+ * guaranteed to be referenced by the Huffman codewords of multiple symbols.
+ * And while the LZX compression format does not allow codes longer than 16
+ * bits, a table of size (2 ** 16) = 65536 entries would be too slow to create.
+ *
+ * There are several different ways to make it possible to look up the symbols
+ * for codewords longer than @table_bits. One way is to make the entries for
+ * the prefixes of length @table_bits of those entries be pointers to additional
+ * decoding tables that are indexed by some number of additional bits of the
+ * codeword. The technique used here is a bit simpler, however: just store the
+ * needed subtrees of the Huffman tree in the decoding table after the lookup
+ * entries, beginning at index (2**table_bits). Real pointers are replaced by
+ * indices into the decoding table, and symbol entries are distinguished from
+ * pointers by the fact that values less than @num_syms must be symbol values.
+ */
+int
+make_huffman_decode_table(u16 *decode_table, unsigned num_syms,
+ unsigned table_bits, const u8 *lens,
+ unsigned max_codeword_len)
+{
+ unsigned len_counts[max_codeword_len + 1];
+ u16 sorted_syms[num_syms];
+ unsigned offsets[max_codeword_len + 1];
+ const unsigned table_num_entries = 1 << table_bits;
+ int left;
+ unsigned decode_table_pos;
+ void *decode_table_ptr;
+ unsigned sym_idx;
+ unsigned codeword_len;
+ unsigned stores_per_loop;
+
+#ifdef USE_LONG_FILL
+ const unsigned entries_per_long = sizeof(unsigned long) / sizeof(decode_table[0]);
+#endif
+
+#ifdef USE_SSE2_FILL
+ const unsigned entries_per_xmm = sizeof(__m128i) / sizeof(decode_table[0]);
+#endif
+
+ wimlib_assert2((uintptr_t)decode_table % DECODE_TABLE_ALIGNMENT == 0);
+
+ /* accumulate lengths for codes */
+ for (unsigned i = 0; i <= max_codeword_len; i++)
+ len_counts[i] = 0;
+
+ for (unsigned sym = 0; sym < num_syms; sym++) {
+ wimlib_assert2(lens[sym] <= max_codeword_len);
+ len_counts[lens[sym]]++;
+ }
+
+ /* check for an over-subscribed or incomplete set of lengths */
+ left = 1;
+ for (unsigned len = 1; len <= max_codeword_len; len++) {
+ left <<= 1;
+ left -= len_counts[len];
+ if (unlikely(left < 0)) { /* over-subscribed */
+ DEBUG("Invalid Huffman code (over-subscribed)");
+ return -1;
+ }
+ }
+
+ if (unlikely(left != 0)) /* incomplete set */{
+ if (left == 1 << max_codeword_len) {
+ /* Empty code--- okay in XPRESS and LZX */
+ memset(decode_table, 0,
+ table_num_entries * sizeof(decode_table[0]));
+ return 0;
+ } else {
+ DEBUG("Invalid Huffman code (incomplete set)");
+ return -1;
+ }
+ }
+
+ /* Generate offsets into symbol table for each length for sorting */
+ offsets[1] = 0;
+ for (unsigned len = 1; len < max_codeword_len; len++)
+ offsets[len + 1] = offsets[len] + len_counts[len];
+
+ /* Sort symbols primarily by length and secondarily by symbol order.
+ * This is basically a count-sort over the codeword lengths. */
+ for (unsigned sym = 0; sym < num_syms; sym++)
+ if (lens[sym] != 0)
+ sorted_syms[offsets[lens[sym]]++] = sym;
+
+ /* Fill entries for codewords short enough for a direct mapping. We can
+ * take advantage of the ordering of the codewords, since the Huffman
+ * code is canonical. It must be the case that all the codewords of
+ * some length L numerically precede all the codewords of length L + 1.
+ * Furthermore, if we have 2 symbols A and B with the same codeword
+ * length but symbol A is sorted before symbol B, then then we know that
+ * the codeword for A numerically precedes the codeword for B. */
+ decode_table_ptr = decode_table;
+ sym_idx = 0;
+ codeword_len = 1;
+#ifdef USE_SSE2_FILL
+ /* Fill in the Huffman decode table entries one 128-bit vector at a
+ * time. This is 8 entries per store. */
+ stores_per_loop = (1 << (table_bits - codeword_len)) / entries_per_xmm;
+ for (; stores_per_loop != 0; codeword_len++, stores_per_loop >>= 1) {
+ unsigned end_sym_idx = sym_idx + len_counts[codeword_len];
+ for (; sym_idx < end_sym_idx; sym_idx++) {
+ /* Note: unlike in the 'long' version below, the __m128i
+ * type already has __attribute__((may_alias)), so using
+ * it to access the decode table, which is an array of
+ * unsigned shorts, will not violate strict aliasing. */
+ u16 sym;
+ __m128i v;
+ __m128i *p;
+ unsigned n;
+
+ sym = sorted_syms[sym_idx];
+
+ v = _mm_set1_epi16(sym);
+ p = (__m128i*)decode_table_ptr;
+ n = stores_per_loop;
+ do {
+ *p++ = v;
+ } while (--n);
+ decode_table_ptr = p;
+ }
+ }
+#endif /* USE_SSE2_FILL */
+
+#ifdef USE_LONG_FILL
+ /* Fill in the Huffman decode table entries one 'unsigned long' at a
+ * time. On 32-bit systems this is 2 entries per store, while on 64-bit
+ * systems this is 4 entries per store. */
+ stores_per_loop = (1 << (table_bits - codeword_len)) / entries_per_long;
+ for (; stores_per_loop != 0; codeword_len++, stores_per_loop >>= 1) {
+ unsigned end_sym_idx = sym_idx + len_counts[codeword_len];
+ for (; sym_idx < end_sym_idx; sym_idx++) {
+
+ /* Accessing the array of unsigned shorts as unsigned
+ * longs would violate strict aliasing and would require
+ * compiling the code with -fno-strict-aliasing to
+ * guarantee correctness. To work around this problem,
+ * use the gcc 'may_alias' extension to define a special
+ * unsigned long type that may alias any other in-memory
+ * variable. */
+ typedef unsigned long __attribute__((may_alias)) aliased_long_t;
+
+ u16 sym;
+ aliased_long_t *p;
+ aliased_long_t v;
+ unsigned n;
+
+ sym = sorted_syms[sym_idx];
+
+ BUILD_BUG_ON(sizeof(aliased_long_t) != 4 &&
+ sizeof(aliased_long_t) != 8);
+
+ v = sym;
+ if (sizeof(aliased_long_t) >= 4)
+ v |= v << 16;
+ if (sizeof(aliased_long_t) >= 8) {
+ /* This may produce a compiler warning if an
+ * aliased_long_t is 32 bits, but this won't be
+ * executed unless an aliased_long_t is at least
+ * 64 bits anyway. */
+ v |= v << 32;
+ }
+
+ p = (aliased_long_t *)decode_table_ptr;
+ n = stores_per_loop;
+
+ do {
+ *p++ = v;
+ } while (--n);
+ decode_table_ptr = p;
+ }
+ }
+#endif /* USE_LONG_FILL */
+
+ /* Fill in the Huffman decode table entries one 16-bit integer at a
+ * time. */
+ stores_per_loop = (1 << (table_bits - codeword_len));
+ for (; stores_per_loop != 0; codeword_len++, stores_per_loop >>= 1) {
+ unsigned end_sym_idx = sym_idx + len_counts[codeword_len];
+ for (; sym_idx < end_sym_idx; sym_idx++) {
+ u16 sym;
+ u16 *p;
+ unsigned n;
+
+ sym = sorted_syms[sym_idx];
+
+ p = (u16*)decode_table_ptr;
+ n = stores_per_loop;
+
+ do {
+ *p++ = sym;
+ } while (--n);
+
+ decode_table_ptr = p;
+ }
+ }
+
+ /* If we've filled in the entire table, we are done. Otherwise, there
+ * are codes longer than table bits that we need to store in the
+ * tree-like structure at the end of the table rather than directly in
+ * the main decode table itself. */
+
+ decode_table_pos = (u16*)decode_table_ptr - decode_table;
+ if (decode_table_pos != table_num_entries) {
+ unsigned j;
+ unsigned next_free_tree_slot;
+ unsigned cur_codeword;
+
+ wimlib_assert2(decode_table_pos < table_num_entries);
+
+ /* Fill in the remaining entries, which correspond to codes
+ * longer than @table_bits.
+ *
+ * First, zero out the rest of the entries. This is necessary
+ * so that the entries appear as "unallocated" in the next part.
+ * */
+ j = decode_table_pos;
+ do {
+ decode_table[j] = 0;
+ } while (++j != table_num_entries);
+
+ /* Assert that 2**table_bits is at least num_syms. If this
+ * wasn't the case, we wouldn't be able to distinguish pointer
+ * entries from symbol entries. */
+ wimlib_assert2(table_num_entries >= num_syms);
+
+
+ /* The tree nodes are allocated starting at decode_table[1 <<
+ * table_bits]. Remember that the full size of the table,
+ * including the extra space for the tree nodes, is actually
+ * 2**table_bits + 2 * num_syms slots, while table_num_entries
+ * is only 2**table_bits. */
+ next_free_tree_slot = table_num_entries;
+
+ /* The current Huffman codeword */
+ cur_codeword = decode_table_pos << 1;
+
+ /* Go through every codeword of length greater than @table_bits,
+ * primarily in order of codeword length and secondarily in
+ * order of symbol. */
+ wimlib_assert2(codeword_len == table_bits + 1);
+ for (; codeword_len <= max_codeword_len; codeword_len++, cur_codeword <<= 1)
+ {
+ unsigned end_sym_idx = sym_idx + len_counts[codeword_len];
+ for (; sym_idx < end_sym_idx; sym_idx++, cur_codeword++) {
+ unsigned sym = sorted_syms[sym_idx];
+ unsigned extra_bits = codeword_len - table_bits;
+
+ /* index of the current node; find it from the
+ * prefix of the current Huffman codeword. */
+ unsigned node_idx = cur_codeword >> extra_bits;
+ wimlib_assert2(node_idx < table_num_entries);
+
+ /* Go through each bit of the current Huffman
+ * codeword beyond the prefix of length
+ * @table_bits and walk the tree, allocating any
+ * slots that have not yet been allocated. */
+ do {
+
+ /* If the current tree node points to
+ * nowhere but we need to follow it,
+ * allocate a new node for it to point
+ * to. */
+ if (decode_table[node_idx] == 0) {
+ decode_table[node_idx] = next_free_tree_slot;
+ decode_table[next_free_tree_slot++] = 0;
+ decode_table[next_free_tree_slot++] = 0;
+ wimlib_assert2(next_free_tree_slot <=
+ table_num_entries + 2 * num_syms);
+ }
+
+ /* Set node_idx to left child */
+ node_idx = decode_table[node_idx];
+
+ /* Is the next bit 0 or 1? If 0, go left
+ * (already done). If 1, go right by
+ * incrementing node_idx. */
+ --extra_bits;
+ node_idx += (cur_codeword >> extra_bits) & 1;
+ } while (extra_bits != 0);
+
+ /* node_idx is now the index of the leaf entry
+ * into which the actual symbol will go. */
+ decode_table[node_idx] = sym;
+
+ /* Note: cur_codeword is always incremented at
+ * the end of this loop because this is how
+ * canonical Huffman codes are generated (add 1
+ * for each code, then left shift whenever the
+ * code length increases) */
+ }
+ }
+ }
+ return 0;
+}
+
+/* Reads a Huffman-encoded symbol from the bistream when the number of remaining
+ * bits is less than the maximum codeword length. */
+int
+read_huffsym_near_end_of_input(struct input_bitstream *istream,
+ const u16 decode_table[],
+ const u8 lens[],
+ unsigned num_syms,
+ unsigned table_bits,
+ unsigned *n)
+{
+ unsigned bitsleft = istream->bitsleft;
+ unsigned key_size;
+ u16 sym;
+ u16 key_bits;
+
+ if (table_bits > bitsleft) {
+ key_size = bitsleft;
+ bitsleft = 0;
+ key_bits = bitstream_peek_bits(istream, key_size) <<
+ (table_bits - key_size);
+ } else {
+ key_size = table_bits;
+ bitsleft -= table_bits;
+ key_bits = bitstream_peek_bits(istream, table_bits);
+ }
+
+ sym = decode_table[key_bits];
+ if (sym >= num_syms) {
+ bitstream_remove_bits(istream, key_size);
+ do {
+ if (bitsleft == 0)
+ return -1;
+ key_bits = sym + bitstream_peek_bits(istream, 1);
+ bitstream_remove_bits(istream, 1);
+ bitsleft--;
+ } while ((sym = decode_table[key_bits]) >= num_syms);
+ } else {
+ bitstream_remove_bits(istream, lens[sym]);
+ }
+ *n = sym;
+ return 0;
+}
git://wimlib.net / wimlib / blobdiff