diff options
Diffstat (limited to 'c/enc/encode.c')
| -rw-r--r-- | c/enc/encode.c | 48 |
1 files changed, 36 insertions, 12 deletions
diff --git a/c/enc/encode.c b/c/enc/encode.c index 563c827..623b88f 100644 --- a/c/enc/encode.c +++ b/c/enc/encode.c @@ -167,6 +167,14 @@ BROTLI_BOOL BrotliEncoderSetParameter( state->params.large_window = TO_BROTLI_BOOL(!!value); return BROTLI_TRUE; + case BROTLI_PARAM_NPOSTFIX: + state->params.dist.distance_postfix_bits = value; + return BROTLI_TRUE; + + case BROTLI_PARAM_NDIRECT: + state->params.dist.num_direct_distance_codes = value; + return BROTLI_TRUE; + default: return BROTLI_FALSE; } } @@ -636,26 +644,42 @@ static void WriteMetaBlockInternal(MemoryManager* m, } static void ChooseDistanceParams(BrotliEncoderParams* params) { - /* NDIRECT, NPOSTFIX must be both zero for qualities - up to MIN_QUALITY_FOR_BLOCK_SPLIT == 3. */ - uint32_t num_direct_distance_codes = 0; uint32_t distance_postfix_bits = 0; + uint32_t num_direct_distance_codes = 0; uint32_t alphabet_size; size_t max_distance = BROTLI_MAX_DISTANCE; - if (params->quality >= MIN_QUALITY_FOR_RECOMPUTE_DISTANCE_PREFIXES && - params->mode == BROTLI_MODE_FONT) { - num_direct_distance_codes = 12; - distance_postfix_bits = 1; - max_distance = (1U << 27) + 4; + if (params->quality >= MIN_QUALITY_FOR_NONZERO_DISTANCE_PARAMS) { + uint32_t ndirect_msb; + if (params->mode == BROTLI_MODE_FONT) { + distance_postfix_bits = 1; + num_direct_distance_codes = 12; + } else { + distance_postfix_bits = params->dist.distance_postfix_bits; + num_direct_distance_codes = params->dist.num_direct_distance_codes; + } + ndirect_msb = (num_direct_distance_codes >> distance_postfix_bits) & 0x0F; + if (distance_postfix_bits > BROTLI_MAX_NPOSTFIX || + num_direct_distance_codes > BROTLI_MAX_NDIRECT || + (ndirect_msb << distance_postfix_bits) != num_direct_distance_codes) { + distance_postfix_bits = 0; + num_direct_distance_codes = 0; + } + max_distance = num_direct_distance_codes + + (1U << (BROTLI_MAX_DISTANCE_BITS + distance_postfix_bits + 2)) - + (1U << (distance_postfix_bits + 2)); } alphabet_size = BROTLI_DISTANCE_ALPHABET_SIZE( num_direct_distance_codes, distance_postfix_bits, BROTLI_MAX_DISTANCE_BITS); if (params->large_window) { - max_distance = BROTLI_MAX_ALLOWED_DISTANCE; - if (num_direct_distance_codes != 0 || distance_postfix_bits != 0) { + /* The maximum distance is set so that no distance symbol used can encode + a distance larger than BROTLI_MAX_ALLOWED_DISTANCE with all + its extra bits set. */ + const uint32_t bound_ndirect[BROTLI_MAX_NDIRECT + 1] = {1, 6, 16, 36}; + max_distance = (1U << 31) - 32; + if (num_direct_distance_codes >= bound_ndirect[distance_postfix_bits]) { max_distance = (3U << 29) - 4; } alphabet_size = BROTLI_DISTANCE_ALPHABET_SIZE( @@ -663,8 +687,8 @@ static void ChooseDistanceParams(BrotliEncoderParams* params) { BROTLI_LARGE_MAX_DISTANCE_BITS); } - params->dist.num_direct_distance_codes = num_direct_distance_codes; params->dist.distance_postfix_bits = distance_postfix_bits; + params->dist.num_direct_distance_codes = num_direct_distance_codes; params->dist.alphabet_size = alphabet_size; params->dist.max_distance = max_distance; } @@ -710,8 +734,8 @@ static void BrotliEncoderInitParams(BrotliEncoderParams* params) { params->size_hint = 0; params->disable_literal_context_modeling = BROTLI_FALSE; BrotliInitEncoderDictionary(¶ms->dictionary); - params->dist.num_direct_distance_codes = 0; params->dist.distance_postfix_bits = 0; + params->dist.num_direct_distance_codes = 0; params->dist.alphabet_size = BROTLI_DISTANCE_ALPHABET_SIZE(0, 0, BROTLI_MAX_DISTANCE_BITS); params->dist.max_distance = BROTLI_MAX_DISTANCE; |