diff options
Diffstat (limited to 'src/liblzma/lzma/lzma_encoder_optimum_fast.c')
| -rw-r--r-- | src/liblzma/lzma/lzma_encoder_optimum_fast.c | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/src/liblzma/lzma/lzma_encoder_optimum_fast.c b/src/liblzma/lzma/lzma_encoder_optimum_fast.c new file mode 100644 index 0000000..6c53d2b --- /dev/null +++ b/src/liblzma/lzma/lzma_encoder_optimum_fast.c @@ -0,0 +1,170 @@ +/////////////////////////////////////////////////////////////////////////////// +// +/// \file lzma_encoder_optimum_fast.c +// +// Author: Igor Pavlov +// +// This file has been put into the public domain. +// You can do whatever you want with this file. +// +/////////////////////////////////////////////////////////////////////////////// + +#include "lzma_encoder_private.h" +#include "memcmplen.h" + + +#define change_pair(small_dist, big_dist) \ + (((big_dist) >> 7) > (small_dist)) + + +extern void +lzma_lzma_optimum_fast(lzma_lzma1_encoder *restrict coder, + lzma_mf *restrict mf, + uint32_t *restrict back_res, uint32_t *restrict len_res) +{ + const uint32_t nice_len = mf->nice_len; + + uint32_t len_main; + uint32_t matches_count; + if (mf->read_ahead == 0) { + len_main = mf_find(mf, &matches_count, coder->matches); + } else { + assert(mf->read_ahead == 1); + len_main = coder->longest_match_length; + matches_count = coder->matches_count; + } + + const uint8_t *buf = mf_ptr(mf) - 1; + const uint32_t buf_avail = my_min(mf_avail(mf) + 1, MATCH_LEN_MAX); + + if (buf_avail < 2) { + // There's not enough input left to encode a match. + *back_res = UINT32_MAX; + *len_res = 1; + return; + } + + // Look for repeated matches; scan the previous four match distances + uint32_t rep_len = 0; + uint32_t rep_index = 0; + + for (uint32_t i = 0; i < REPS; ++i) { + // Pointer to the beginning of the match candidate + const uint8_t *const buf_back = buf - coder->reps[i] - 1; + + // If the first two bytes (2 == MATCH_LEN_MIN) do not match, + // this rep is not useful. + if (not_equal_16(buf, buf_back)) + continue; + + // The first two bytes matched. + // Calculate the length of the match. + const uint32_t len = lzma_memcmplen( + buf, buf_back, 2, buf_avail); + + // If we have found a repeated match that is at least + // nice_len long, return it immediately. + if (len >= nice_len) { + *back_res = i; + *len_res = len; + mf_skip(mf, len - 1); + return; + } + + if (len > rep_len) { + rep_index = i; + rep_len = len; + } + } + + // We didn't find a long enough repeated match. Encode it as a normal + // match if the match length is at least nice_len. + if (len_main >= nice_len) { + *back_res = coder->matches[matches_count - 1].dist + REPS; + *len_res = len_main; + mf_skip(mf, len_main - 1); + return; + } + + uint32_t back_main = 0; + if (len_main >= 2) { + back_main = coder->matches[matches_count - 1].dist; + + while (matches_count > 1 && len_main == + coder->matches[matches_count - 2].len + 1) { + if (!change_pair(coder->matches[ + matches_count - 2].dist, + back_main)) + break; + + --matches_count; + len_main = coder->matches[matches_count - 1].len; + back_main = coder->matches[matches_count - 1].dist; + } + + if (len_main == 2 && back_main >= 0x80) + len_main = 1; + } + + if (rep_len >= 2) { + if (rep_len + 1 >= len_main + || (rep_len + 2 >= len_main + && back_main > (UINT32_C(1) << 9)) + || (rep_len + 3 >= len_main + && back_main > (UINT32_C(1) << 15))) { + *back_res = rep_index; + *len_res = rep_len; + mf_skip(mf, rep_len - 1); + return; + } + } + + if (len_main < 2 || buf_avail <= 2) { + *back_res = UINT32_MAX; + *len_res = 1; + return; + } + + // Get the matches for the next byte. If we find a better match, + // the current byte is encoded as a literal. + coder->longest_match_length = mf_find(mf, + &coder->matches_count, coder->matches); + + if (coder->longest_match_length >= 2) { + const uint32_t new_dist = coder->matches[ + coder->matches_count - 1].dist; + + if ((coder->longest_match_length >= len_main + && new_dist < back_main) + || (coder->longest_match_length == len_main + 1 + && !change_pair(back_main, new_dist)) + || (coder->longest_match_length > len_main + 1) + || (coder->longest_match_length + 1 >= len_main + && len_main >= 3 + && change_pair(new_dist, back_main))) { + *back_res = UINT32_MAX; + *len_res = 1; + return; + } + } + + // In contrast to LZMA SDK, dictionary could not have been moved + // between mf_find() calls, thus it is safe to just increment + // the old buf pointer instead of recalculating it with mf_ptr(). + ++buf; + + const uint32_t limit = my_max(2, len_main - 1); + + for (uint32_t i = 0; i < REPS; ++i) { + if (memcmp(buf, buf - coder->reps[i] - 1, limit) == 0) { + *back_res = UINT32_MAX; + *len_res = 1; + return; + } + } + + *back_res = back_main + REPS; + *len_res = len_main; + mf_skip(mf, len_main - 2); + return; +} |