diff options
| -rw-r--r-- | src/liblzma/lz/lz_decoder.c | 43 | ||||
| -rw-r--r-- | src/liblzma/lz/lz_decoder.h | 101 | ||||
| -rw-r--r-- | src/liblzma/lzma/lzma_decoder.c | 4 |
3 files changed, 88 insertions, 60 deletions
diff --git a/src/liblzma/lz/lz_decoder.c b/src/liblzma/lz/lz_decoder.c index 73bf20d9..92913f22 100644 --- a/src/liblzma/lz/lz_decoder.c +++ b/src/liblzma/lz/lz_decoder.c @@ -53,9 +53,10 @@ typedef struct { static void lz_decoder_reset(lzma_coder *coder) { - coder->dict.pos = 0; + coder->dict.pos = 2 * LZ_DICT_REPEAT_MAX; coder->dict.full = 0; - coder->dict.buf[coder->dict.size - 1] = '\0'; + coder->dict.buf[2 * LZ_DICT_REPEAT_MAX - 1] = '\0'; + coder->dict.has_wrapped = false; coder->dict.need_reset = false; return; } @@ -69,8 +70,15 @@ decode_buffer(lzma_coder *coder, { while (true) { // Wrap the dictionary if needed. - if (coder->dict.pos == coder->dict.size) - coder->dict.pos = 0; + if (coder->dict.pos == coder->dict.size) { + // See the comment of #define LZ_DICT_REPEAT_MAX. + coder->dict.pos = LZ_DICT_REPEAT_MAX; + coder->dict.has_wrapped = true; + memcpy(coder->dict.buf, coder->dict.buf + + coder->dict.size + - LZ_DICT_REPEAT_MAX, + LZ_DICT_REPEAT_MAX); + } // Store the current dictionary position. It is needed to know // where to start copying to the out[] buffer. @@ -252,21 +260,31 @@ lzma_lz_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator, // dictionary to the output buffer, since applications are // recommended to give aligned buffers to liblzma. // + // Reserve 2 * LZ_DICT_REPEAT_MAX bytes of extra space which is + // needed for alloc_size. + // // Avoid integer overflow. - if (lz_options.dict_size > SIZE_MAX - 15) + if (lz_options.dict_size > SIZE_MAX - 15 - 2 * LZ_DICT_REPEAT_MAX) return LZMA_MEM_ERROR; lz_options.dict_size = (lz_options.dict_size + 15) & ~((size_t)(15)); + // Reserve extra space as explained in the comment + // of #define LZ_DICT_REPEAT_MAX. + const size_t alloc_size + = lz_options.dict_size + 2 * LZ_DICT_REPEAT_MAX; + // Allocate and initialize the dictionary. - if (coder->dict.size != lz_options.dict_size) { + if (coder->dict.size != alloc_size) { lzma_free(coder->dict.buf, allocator); - coder->dict.buf - = lzma_alloc(lz_options.dict_size, allocator); + coder->dict.buf = lzma_alloc(alloc_size, allocator); if (coder->dict.buf == NULL) return LZMA_MEM_ERROR; - coder->dict.size = lz_options.dict_size; + // NOTE: Yes, alloc_size, not lz_options.dict_size. The way + // coder->dict.full is updated will take care that we will + // still reject distances larger than lz_options.dict_size. + coder->dict.size = alloc_size; } lz_decoder_reset(next->coder); @@ -279,9 +297,12 @@ lzma_lz_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator, const size_t copy_size = my_min(lz_options.preset_dict_size, lz_options.dict_size); const size_t offset = lz_options.preset_dict_size - copy_size; - memcpy(coder->dict.buf, lz_options.preset_dict + offset, + memcpy(coder->dict.buf + coder->dict.pos, + lz_options.preset_dict + offset, copy_size); - coder->dict.pos = copy_size; + + // dict.pos isn't zero after lz_decoder_reset(). + coder->dict.pos += copy_size; coder->dict.full = copy_size; } diff --git a/src/liblzma/lz/lz_decoder.h b/src/liblzma/lz/lz_decoder.h index 3b41649c..da273480 100644 --- a/src/liblzma/lz/lz_decoder.h +++ b/src/liblzma/lz/lz_decoder.h @@ -16,10 +16,28 @@ #include "common.h" +/// Maximum length of a match rounded up to a nice power of 2 which is +/// a good size for aligned memcpy(). The allocated dictionary buffer will +/// be 2 * LZ_DICT_REPEAT_MAX bytes larger than the actual dictionary size: +/// +/// (1) Every time the decoder reaches the end of the dictionary buffer, +/// the last LZ_DICT_REPEAT_MAX bytes will be copied to the beginning. +/// This way dict_repeat() will only need to copy from one place, +/// never from both the end and beginning of the buffer. +/// +/// (2) The other LZ_DICT_REPEAT_MAX bytes is kept as a buffer between +/// the oldest byte still in the dictionary and the current write +/// position. This way dict_repeat(dict, dict->size - 1, &len) +/// won't need memmove() as the copying cannot overlap. +/// +/// Note that memcpy() still cannot be used if distance < len. +/// +/// LZMA's longest match length is 273 so pick a multiple of 16 above that. +#define LZ_DICT_REPEAT_MAX 288 + + typedef struct { - /// Pointer to the dictionary buffer. It can be an allocated buffer - /// internal to liblzma, or it can a be a buffer given by the - /// application when in single-call mode (not implemented yet). + /// Pointer to the dictionary buffer. uint8_t *buf; /// Write position in dictionary. The next byte will be written to @@ -34,9 +52,16 @@ typedef struct { /// Write limit size_t limit; - /// Size of the dictionary + /// Allocated size of buf. This is 2 * LZ_DICT_REPEAT_MAX bytes + /// larger than the actual dictionary size. This is enforced by + /// how the value for "full" is set; it can be at most + /// "size - 2 * LZ_DICT_REPEAT_MAX". size_t size; + /// True once the dictionary has become full and the writing position + /// has been wrapped in decode_buffer() in lz_decoder.c. + bool has_wrapped; + /// True when dictionary should be reset before decoding more data. bool need_reset; @@ -102,7 +127,16 @@ static inline uint8_t dict_get(const lzma_dict *const dict, const uint32_t distance) { return dict->buf[dict->pos - distance - 1 - + (distance < dict->pos ? 0 : dict->size)]; + + (distance < dict->pos + ? 0 : dict->size - LZ_DICT_REPEAT_MAX)]; +} + + +/// Optimized version of dict_get(dict, 0) +static inline uint8_t +dict_get0(const lzma_dict *const dict) +{ + return dict->buf[dict->pos - 1]; } @@ -131,50 +165,27 @@ dict_repeat(lzma_dict *dict, uint32_t distance, uint32_t *len) uint32_t left = my_min(dict_avail, *len); *len -= left; + size_t back = dict->pos - distance - 1; + if (distance >= dict->pos) + back += dict->size - LZ_DICT_REPEAT_MAX; + // Repeat a block of data from the history. Because memcpy() is faster // than copying byte by byte in a loop, the copying process gets split - // into three cases. + // into two cases. if (distance < left) { // Source and target areas overlap, thus we can't use // memcpy() nor even memmove() safely. do { - dict->buf[dict->pos] = dict_get(dict, distance); - ++dict->pos; + dict->buf[dict->pos++] = dict->buf[back++]; } while (--left > 0); - - } else if (distance < dict->pos) { - // The easiest and fastest case - memcpy(dict->buf + dict->pos, - dict->buf + dict->pos - distance - 1, - left); - dict->pos += left; - } else { - // The bigger the dictionary, the more rare this - // case occurs. We need to "wrap" the dict, thus - // we might need two memcpy() to copy all the data. - assert(dict->full == dict->size); - const uint32_t copy_pos - = dict->pos - distance - 1 + dict->size; - uint32_t copy_size = dict->size - copy_pos; - - if (copy_size < left) { - memmove(dict->buf + dict->pos, dict->buf + copy_pos, - copy_size); - dict->pos += copy_size; - copy_size = left - copy_size; - memcpy(dict->buf + dict->pos, dict->buf, copy_size); - dict->pos += copy_size; - } else { - memmove(dict->buf + dict->pos, dict->buf + copy_pos, - left); - dict->pos += left; - } + memcpy(dict->buf + dict->pos, dict->buf + back, left); + dict->pos += left; } // Update how full the dictionary is. - if (dict->full < dict->pos) - dict->full = dict->pos; + if (!dict->has_wrapped) + dict->full = dict->pos - 2 * LZ_DICT_REPEAT_MAX; return unlikely(*len != 0); } @@ -185,8 +196,8 @@ dict_put(lzma_dict *dict, uint8_t byte) { dict->buf[dict->pos++] = byte; - if (dict->pos > dict->full) - dict->full = dict->pos; + if (!dict->has_wrapped) + dict->full = dict->pos - 2 * LZ_DICT_REPEAT_MAX; } @@ -198,11 +209,7 @@ dict_put_safe(lzma_dict *dict, uint8_t byte) if (dict->pos == dict->limit) return true; - dict->buf[dict->pos++] = byte; - - if (dict->pos > dict->full) - dict->full = dict->pos; - + dict_put(dict, byte); return false; } @@ -226,8 +233,8 @@ dict_write(lzma_dict *restrict dict, const uint8_t *restrict in, *left -= lzma_bufcpy(in, in_pos, in_size, dict->buf, &dict->pos, dict->limit); - if (dict->pos > dict->full) - dict->full = dict->pos; + if (!dict->has_wrapped) + dict->full = dict->pos - 2 * LZ_DICT_REPEAT_MAX; return; } diff --git a/src/liblzma/lzma/lzma_decoder.c b/src/liblzma/lzma/lzma_decoder.c index c5049a48..81149006 100644 --- a/src/liblzma/lzma/lzma_decoder.c +++ b/src/liblzma/lzma/lzma_decoder.c @@ -360,7 +360,7 @@ lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr, // lc params. probs = literal_subcoder(coder->literal, literal_context_bits, literal_pos_mask, - dict.pos, dict_get(&dict, 0)); + dict.pos, dict_get0(&dict)); if (is_literal_state(state)) { update_literal_normal(state); @@ -685,7 +685,7 @@ slow: probs = literal_subcoder(coder->literal, literal_context_bits, literal_pos_mask, - dict.pos, dict_get(&dict, 0)); + dict.pos, dict_get0(&dict)); symbol = 1; if (is_literal_state(state)) { |