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Align distance code meaning in the brotli encoder.

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Two different definitions (offset by 1) were used in
command.h and hash.h. Now they have been made the same,
also consistent with the spec (e.g. 0 means use previous dist, etc...)
This commit is contained in:
Zoltan Szabadka 2015-05-07 17:40:00 +02:00
parent fa2c6df4f5
commit 12eb9bfd70
3 changed files with 11 additions and 11 deletions
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15
enc/backward_references.cc
View File

@ -172,16 +172,17 @@ void CreateBackwardReferences(size_t num_bytes,
apply_random_heuristics =
i + 2 * best_len + random_heuristics_window_size;
max_distance = std::min(i + i_diff, max_backward_limit);
int distance_code = best_dist + 16;
// The first 16 codes are special shortcodes, and the minimum offset is 1.
int distance_code = best_dist + 15;
if (best_dist <= max_distance) {
if (best_dist == dist_cache[0]) {
distance_code = 1;
distance_code = 0;
} else if (best_dist == dist_cache[1]) {
distance_code = 2;
distance_code = 1;
} else if (best_dist == dist_cache[2]) {
distance_code = 3;
distance_code = 2;
} else if (best_dist == dist_cache[3]) {
distance_code = 4;
distance_code = 3;
} else if (quality > 3 && best_dist >= 6) {
for (int k = 4; k < kNumDistanceShortCodes; ++k) {
int idx = kDistanceCacheIndex[k];
@ -191,12 +192,12 @@ void CreateBackwardReferences(size_t num_bytes,
11, 11, 11, 11,
12, 12, 12, 12 };
if (best_dist == candidate && best_dist >= kLimits[k]) {
distance_code = k + 1;
distance_code = k;
break;
}
}
}
if (distance_code > 1) {
if (distance_code > 0) {
dist_cache[3] = dist_cache[2];
dist_cache[2] = dist_cache[1];
dist_cache[1] = dist_cache[0];

6
enc/command.h
View File

@ -24,7 +24,6 @@ namespace brotli {
static inline void GetDistCode(int distance_code,
uint16_t* code, uint32_t* extra) {
distance_code -= 1;
if (distance_code < 16) {
*code = distance_code;
*extra = 0;
@ -106,6 +105,7 @@ static inline void GetLengthCode(int insertlen, int copylen, int distancecode,
struct Command {
Command() {}
// distance_code is e.g. 0 for same-as-last short code, or 16 for offset 1.
Command(int insertlen, int copylen, int copylen_code, int distance_code)
: insert_len_(insertlen), copy_len_(copylen) {
GetDistCode(distance_code, &dist_prefix_, &dist_extra_);
@ -120,12 +120,12 @@ struct Command {
int DistanceCode() const {
if (dist_prefix_ < 16) {
return dist_prefix_ + 1;
return dist_prefix_;
}
int nbits = dist_extra_ >> 24;
int extra = dist_extra_ & 0xffffff;
int prefix = dist_prefix_ - 12 - 2 * nbits;
return (prefix << nbits) + extra + 13;
return (prefix << nbits) + extra + 12;
}
int DistanceContext() const {

1
enc/prefix.h
View File

@ -62,7 +62,6 @@ inline void PrefixEncodeCopyDistance(int distance_code,
int postfix_bits,
uint16_t* code,
uint32_t* extra_bits) {
distance_code -= 1;
if (distance_code < kNumDistanceShortCodes + num_direct_codes) {
*code = distance_code;
*extra_bits = 0;