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Fix edge cases and stability issues in Brotli Base64 entropy coding optimization. #1512

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Fix edge cases and stability issues in Brotli Base64 entropy coding optimization. #1512

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2 changes: 1 addition & 1 deletion c/enc/block_encoder_inc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ static void FN(BuildAndStoreEntropyCodes)(
size_t i;
for (i = 0; i < histograms_size; ++i) {
size_t ix = i * self->histogram_length_;
if (self->histogram_length_ == 256 && is_base64_histogram &&
if (self->histogram_length_ == 256 && is_base64_histogram && i < 256 &&
is_base64_histogram[i]) {
size_t k;
memset(&self->depths_[ix], 0, 256);
Expand Down
24 changes: 19 additions & 5 deletions c/enc/brotli_bit_stream.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1019,11 +1019,25 @@ void BrotliStoreMetaBlock(MemoryManager* m,

{
uint8_t is_base64_histogram[256] = {0};
if (mb->literal_split.num_types > 0) {
size_t b64_type_id = mb->literal_split.num_types - 1;
if (b64_type_id < 256 && (mb->literal_is_base64[b64_type_id >> 3] & (1u << (b64_type_id & 7)))) {
uint32_t b64_histo_id = mb->literal_context_map ? mb->literal_context_map[b64_type_id << 6] : (uint32_t)b64_type_id;
is_base64_histogram[b64_histo_id] = 1;
size_t type_id;
for (type_id = 0; type_id < mb->literal_split.num_types; ++type_id) {
if (type_id < 256 &&
(mb->literal_is_base64[type_id >> 3] & (1u << (type_id & 7)))) {
if (mb->literal_context_map) {
size_t j;
for (j = 0; j < (1u << BROTLI_LITERAL_CONTEXT_BITS); ++j) {
uint32_t b64_histo_id =
mb->literal_context_map[(type_id << BROTLI_LITERAL_CONTEXT_BITS) + j];
if (b64_histo_id < 256) {
is_base64_histogram[b64_histo_id] = 1;
}
}
} else {
uint32_t b64_histo_id = (uint32_t)type_id;
if (b64_histo_id < 256) {
is_base64_histogram[b64_histo_id] = 1;
}
}
}
}

Expand Down
125 changes: 93 additions & 32 deletions c/enc/metablock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -106,6 +106,74 @@ static void ForceBase64LiteralSplits(MemoryManager* m, BlockSplit* split,
split->num_types++;
}

static void AppendBase64Histogram(MemoryManager* m, MetaBlockSplit* mb) {
size_t base64_type_id = mb->literal_split.num_types - 1;
size_t b64_histo_id = mb->literal_histograms_size;
size_t new_context_map_size =
mb->literal_split.num_types << BROTLI_LITERAL_CONTEXT_BITS;
HistogramLiteral* new_histos =
BROTLI_ALLOC(m, HistogramLiteral, mb->literal_histograms_size + 1);
uint32_t* new_context_map =
BROTLI_ALLOC(m, uint32_t, new_context_map_size);
size_t i;
if (BROTLI_IS_OOM(m) || BROTLI_IS_NULL(new_histos) ||
BROTLI_IS_NULL(new_context_map)) {
BROTLI_FREE(m, new_histos);
BROTLI_FREE(m, new_context_map);
return;
}
memcpy(new_histos, mb->literal_histograms,
mb->literal_histograms_size * sizeof(HistogramLiteral));
BROTLI_FREE(m, mb->literal_histograms);
mb->literal_histograms = new_histos;
HistogramClearLiteral(&mb->literal_histograms[b64_histo_id]);
mb->literal_histograms_size++;

if (mb->literal_context_map != NULL) {
memcpy(new_context_map, mb->literal_context_map,
mb->literal_context_map_size * sizeof(uint32_t));
BROTLI_FREE(m, mb->literal_context_map);
} else {
/* If context map was NULL (num_contexts == 1), initialize preceding types */
size_t t;
for (t = 0; t < base64_type_id; ++t) {
for (i = 0; i < 64; ++i) {
new_context_map[(t << 6) + i] = (uint32_t)t;
}
}
}
mb->literal_context_map = new_context_map;
mb->literal_context_map_size = new_context_map_size;
for (i = 0; i < 64; ++i) {
mb->literal_context_map[(base64_type_id << 6) + i] = (uint32_t)b64_histo_id;
}
}

static void MapBase64RegionsToLiteralPositions(
const Command* commands, size_t num_commands, size_t last_flush_pos,
const Base64Region* in_regions, size_t num_in_regions,
Base64Region* out_regions) {
size_t r;
for (r = 0; r < num_in_regions; ++r) {
size_t target_ring_pos = in_regions[r].start_literal_pos;
size_t curr_ring_pos = last_flush_pos;
size_t curr_lit_pos = 0;
size_t i;
for (i = 0; i < num_commands; ++i) {
const Command cmd = commands[i];
if (curr_ring_pos + cmd.insert_len_ >= target_ring_pos) {
size_t offset = target_ring_pos > curr_ring_pos ? target_ring_pos - curr_ring_pos : 0;
curr_lit_pos += offset;
break;
}
curr_lit_pos += cmd.insert_len_;
curr_ring_pos += cmd.insert_len_ + CommandCopyLen(&cmd);
}
out_regions[r].start_literal_pos = curr_lit_pos;
out_regions[r].length = in_regions[r].length;
}
}

void BrotliInitDistanceParams(BrotliDistanceParams* dist_params,
uint32_t npostfix, uint32_t ndirect, BROTLI_BOOL large_window) {
uint32_t alphabet_size_max;
Expand Down Expand Up @@ -223,7 +291,6 @@ void BrotliBuildMetaBlock(MemoryManager* m, const uint8_t* ringbuffer,
uint32_t npostfix;
uint32_t ndirect_msb = 0;
BROTLI_BOOL check_orig = BROTLI_TRUE;
BROTLI_BOOL base64_applied = BROTLI_FALSE;
double best_dist_cost = 1e99;
BrotliDistanceParams orig_params = params->dist;
BrotliDistanceParams new_params = params->dist;
Expand Down Expand Up @@ -273,14 +340,6 @@ void BrotliBuildMetaBlock(MemoryManager* m, const uint8_t* ringbuffer,
&mb->distance_split);
if (BROTLI_IS_OOM(m)) return;

if (num_base64_regions > 0 && mb->literal_split.num_types < 256) {
ForceBase64LiteralSplits(m, &mb->literal_split, base64_regions,
num_base64_regions, pos, mb);
if (!BROTLI_IS_OOM(m)) {
base64_applied = BROTLI_TRUE;
}
}

if (!params->disable_literal_context_modeling) {
literal_context_multiplier = 1 << BROTLI_LITERAL_CONTEXT_BITS;
literal_context_modes =
Expand Down Expand Up @@ -337,26 +396,6 @@ void BrotliBuildMetaBlock(MemoryManager* m, const uint8_t* ringbuffer,
if (BROTLI_IS_OOM(m)) return;
BROTLI_FREE(m, literal_histograms);

if (base64_applied) {
size_t base64_type_id = mb->literal_split.num_types - 1;
size_t b64_histo_id = mb->literal_histograms_size;
HistogramLiteral* new_histos =
BROTLI_ALLOC(m, HistogramLiteral, mb->literal_histograms_size + 1);
if (BROTLI_IS_OOM(m) || BROTLI_IS_NULL(new_histos)) {
return;
}
memcpy(new_histos, mb->literal_histograms,
mb->literal_histograms_size * sizeof(HistogramLiteral));
BROTLI_FREE(m, mb->literal_histograms);
mb->literal_histograms = new_histos;
HistogramClearLiteral(&mb->literal_histograms[b64_histo_id]);
for (i = 0; i < 64; ++i) {
mb->literal_context_map[(base64_type_id << 6) + i] =
(uint32_t)b64_histo_id;
}
mb->literal_histograms_size++;
}

if (params->disable_literal_context_modeling) {
/* Distribute assignment to all contexts. */
for (i = mb->literal_split.num_types; i != 0;) {
Expand All @@ -369,6 +408,21 @@ void BrotliBuildMetaBlock(MemoryManager* m, const uint8_t* ringbuffer,
}
}

if (num_base64_regions > 0 && mb->literal_split.num_types < 256 &&
mb->literal_histograms_size < 256) {
Base64Region local_b64[256];
size_t safe_num_b64 = BROTLI_MIN(size_t, num_base64_regions, 256);
MapBase64RegionsToLiteralPositions(cmds, num_commands, pos,
base64_regions, safe_num_b64,
local_b64);
ForceBase64LiteralSplits(m, &mb->literal_split, local_b64,
safe_num_b64, 0, mb);
if (!BROTLI_IS_OOM(m)) {
AppendBase64Histogram(m, mb);
}
if (BROTLI_IS_OOM(m)) return;
}

BROTLI_DCHECK(mb->distance_context_map == 0);
mb->distance_context_map_size =
mb->distance_split.num_types << BROTLI_DISTANCE_CONTEXT_BITS;
Expand Down Expand Up @@ -658,6 +712,7 @@ static BROTLI_INLINE void BrotliBuildMetaBlockGreedyInternal(
ContextLut literal_context_lut, const size_t num_contexts,
const uint32_t* static_context_map, const Command* commands,
size_t n_commands, MetaBlockSplit* mb) {
const size_t start_pos = pos;
size_t num_literals = 0;
size_t i;
for (i = 0; i < n_commands; ++i) {
Expand Down Expand Up @@ -722,9 +777,15 @@ static BROTLI_INLINE void BrotliBuildMetaBlockGreedyInternal(
if (BROTLI_IS_OOM(m)) return;
}

if (num_base64_regions > 0 && mb->literal_split.num_types < 256) {
ForceBase64LiteralSplits(m, &mb->literal_split, base64_regions,
num_base64_regions, pos, mb);
if (num_base64_regions > 0 && mb->literal_split.num_types < 256 &&
mb->literal_histograms_size + num_contexts <= 256) {
Base64Region local_b64[256];
size_t safe_num_b64 = BROTLI_MIN(size_t, num_base64_regions, 256);
MapBase64RegionsToLiteralPositions(commands, n_commands, start_pos,
base64_regions, safe_num_b64,
local_b64);
ForceBase64LiteralSplits(m, &mb->literal_split, local_b64,
safe_num_b64, 0, mb);
if (BROTLI_IS_OOM(m)) return;
{
size_t num_b64_histos = num_contexts;
Expand Down
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