/* Returns the minimum possible copy length that can improve the cost of any */
/* future position. */
private static unsafe size_t ComputeMinimumCopyLength(float start_cost,
ZopfliNode *nodes,
size_t num_bytes,
size_t pos)
{
/* Compute the minimum possible cost of reaching any future position. */
float min_cost = start_cost;
size_t len = 2;
size_t next_len_bucket = 4;
size_t next_len_offset = 10;
while (pos + len <= num_bytes && nodes[pos + len].u.cost <= min_cost)
{
/* We already reached (pos + len) with no more cost than the minimum
* possible cost of reaching anything from this pos, so there is no point in
* looking for lengths <= len. */
++len;
if (len == next_len_offset)
{
/* We reached the next copy length code bucket, so we add one more
* extra bit to the minimum cost. */
min_cost += 1.0f;
next_len_offset += next_len_bucket;
next_len_bucket *= 2;
}
}
return(len);
}
/* REQUIRES: nodes[pos].cost < kInfinity
* REQUIRES: nodes[0..pos] satisfies that "ZopfliNode array invariant". */
private static unsafe uint ComputeDistanceShortcut(size_t block_start,
size_t pos,
size_t max_backward,
ZopfliNode *nodes)
{
size_t clen = ZopfliNodeCopyLength(&nodes[pos]);
size_t ilen = nodes[pos].insert_length;
size_t dist = ZopfliNodeCopyDistance(&nodes[pos]);
/* Since |block_start + pos| is the end position of the command, the copy part
* starts from |block_start + pos - clen|. Distances that are greater than
* this or greater than |max_backward| are private static unsafe dictionary references, and
* do not update the last distances. Also distance code 0 (last distance)
* does not update the last distances. */
if (pos == 0)
{
return(0);
}
else if (dist + clen <= block_start + pos &&
dist <= max_backward &&
ZopfliNodeDistanceCode(&nodes[pos]) > 0)
{
return((uint)pos);
}
else
{
return(nodes[pos - clen - ilen].u.shortcut);
}
}
private static unsafe uint ZopfliNodeDistanceCode(ZopfliNode *self)
{
uint short_code = self->distance >> 25;
return(short_code == 0
? ZopfliNodeCopyDistance(self) + BROTLI_NUM_DISTANCE_SHORT_CODES - 1
: short_code - 1);
}
private static unsafe size_t ZopfliIterate(size_t num_bytes,
size_t position,
byte *ringbuffer,
size_t ringbuffer_mask,
BrotliEncoderParams *params_,
size_t max_backward_limit,
int *dist_cache,
ZopfliCostModel *model,
uint *num_matches,
BackwardMatch *matches,
ZopfliNode *nodes)
{
size_t max_zopfli_len = MaxZopfliLen(params_);
StartPosQueue queue;
size_t cur_match_pos = 0;
size_t i;
nodes[0].length = 0;
nodes[0].u.cost = 0;
InitStartPosQueue(&queue);
for (i = 0; i + 3 < num_bytes; i++)
{
size_t skip = UpdateNodes(num_bytes, position, i, ringbuffer,
ringbuffer_mask, params_, max_backward_limit, dist_cache,
num_matches[i], &matches[cur_match_pos], model, &queue, nodes);
if (skip < BROTLI_LONG_COPY_QUICK_STEP)
{
skip = 0;
}
cur_match_pos += num_matches[i];
if (num_matches[i] == 1 &&
BackwardMatchLength(&matches[cur_match_pos - 1]) > max_zopfli_len)
{
skip = Math.Max(
BackwardMatchLength(&matches[cur_match_pos - 1]), skip);
}
if (skip > 1)
{
skip--;
while (skip != 0)
{
i++;
if (i + 3 >= num_bytes)
{
break;
}
EvaluateNode(
position, i, max_backward_limit, dist_cache, model, &queue, nodes);
cur_match_pos += num_matches[i];
skip--;
}
}
}
return(ComputeShortestPathFromNodes(num_bytes, nodes));
}
/* REQUIRES: len >= 2, start_pos <= pos */
/* REQUIRES: cost < kInfinity, nodes[start_pos].cost < kInfinity */
/* Maintains the "ZopfliNode array invariant". */
private static unsafe void UpdateZopfliNode(ZopfliNode *nodes, size_t pos,
size_t start_pos, size_t len, size_t len_code, size_t dist,
size_t short_code, float cost)
{
ZopfliNode *next = &nodes[pos + len];
next->length = (uint)(len | ((len + 9u - len_code) << 24));
next->distance = (uint)(dist | (short_code << 25));
next->insert_length = (uint)(pos - start_pos);
next->u.cost = cost;
}
/* REQUIRES: nodes != NULL and len(nodes) >= num_bytes + 1 */
private static unsafe void BrotliZopfliCreateCommands(size_t num_bytes,
size_t block_start,
size_t max_backward_limit,
ZopfliNode *nodes,
int *dist_cache,
size_t *last_insert_len,
Command *commands,
size_t *num_literals)
{
size_t pos = 0;
uint offset = nodes[0].u.next;
size_t i;
for (i = 0; offset != uint.MaxValue; i++)
{
ZopfliNode *next = &nodes[pos + offset];
size_t copy_length = ZopfliNodeCopyLength(next);
size_t insert_length = next->insert_length;
pos += insert_length;
offset = next->u.next;
if (i == 0)
{
insert_length += *last_insert_len;
*last_insert_len = 0;
}
{
size_t distance = ZopfliNodeCopyDistance(next);
size_t len_code = ZopfliNodeLengthCode(next);
size_t max_distance =
Math.Min(block_start + pos, max_backward_limit);
bool is_dictionary = (distance > max_distance);
size_t dist_code = ZopfliNodeDistanceCode(next);
InitCommand(
&commands[i], insert_length, copy_length, len_code, dist_code);
if (!is_dictionary && dist_code > 0)
{
dist_cache[3] = dist_cache[2];
dist_cache[2] = dist_cache[1];
dist_cache[1] = dist_cache[0];
dist_cache[0] = (int)distance;
}
}
*num_literals += insert_length;
pos += copy_length;
}
*last_insert_len += num_bytes - pos;
}
private static unsafe void BrotliInitZopfliNodes(ZopfliNode *array, size_t length)
{
ZopfliNode stub = new ZopfliNode();
size_t i;
stub.length = 1;
stub.distance = 0;
stub.insert_length = 0;
stub.u.cost = kInfinity;
for (i = 0; i < length; ++i)
{
array[i] = stub;
}
}
private static unsafe size_t ComputeShortestPathFromNodes(size_t num_bytes,
ZopfliNode *nodes)
{
size_t index = num_bytes;
size_t num_commands = 0;
while (nodes[index].insert_length == 0 && nodes[index].length == 1)
{
--index;
}
nodes[index].u.next = uint.MaxValue;
while (index != 0)
{
size_t len = ZopfliNodeCommandLength(&nodes[index]);
index -= len;
nodes[index].u.next = (uint)len;
num_commands++;
}
return(num_commands);
}
/* Maintains "ZopfliNode array invariant" and pushes node to the queue, if it
* is eligible. */
private static unsafe void EvaluateNode(
size_t block_start, size_t pos, size_t max_backward_limit,
int *starting_dist_cache, ZopfliCostModel *model,
StartPosQueue *queue, ZopfliNode *nodes)
{
/* Save cost, because ComputeDistanceCache invalidates it. */
float node_cost = nodes[pos].u.cost;
nodes[pos].u.shortcut = ComputeDistanceShortcut(
block_start, pos, max_backward_limit, nodes);
if (node_cost <= ZopfliCostModelGetLiteralCosts(model, 0, pos))
{
PosData posdata;
posdata.pos = pos;
posdata.cost = node_cost;
posdata.costdiff = node_cost -
ZopfliCostModelGetLiteralCosts(model, 0, pos);
ComputeDistanceCache(
pos, starting_dist_cache, nodes, posdata.distance_cache);
StartPosQueuePush(queue, &posdata);
}
}
/* Fills in dist_cache[0..3] with the last four distances (as defined by
* Section 4. of the Spec) that would be used at (block_start + pos) if we
* used the shortest path of commands from block_start, computed from
* nodes[0..pos]. The last four distances at block_start are in
* starting_dist_cache[0..3].
* REQUIRES: nodes[pos].cost < kInfinity
* REQUIRES: nodes[0..pos] satisfies that "ZopfliNode array invariant". */
private static unsafe void ComputeDistanceCache(size_t pos,
int *starting_dist_cache,
ZopfliNode *nodes,
int *dist_cache)
{
int idx = 0;
size_t p = nodes[pos].u.shortcut;
while (idx < 4 && p > 0)
{
size_t ilen = nodes[p].insert_length;
size_t clen = ZopfliNodeCopyLength(&nodes[p]);
size_t dist = ZopfliNodeCopyDistance(&nodes[p]);
dist_cache[idx++] = (int)dist;
/* Because of prerequisite, p >= clen + ilen >= 2. */
p = nodes[p - clen - ilen].u.shortcut;
}
for (; idx < 4; ++idx)
{
dist_cache[idx] = *starting_dist_cache++;
}
}
/* REQUIRES: nodes != NULL and len(nodes) >= num_bytes + 1 */
private static unsafe size_t BrotliZopfliComputeShortestPath(ref MemoryManager m,
size_t num_bytes,
size_t position,
byte *ringbuffer,
size_t ringbuffer_mask,
BrotliEncoderParams *params_,
size_t max_backward_limit,
int *dist_cache,
HasherHandle hasher,
ZopfliNode *nodes)
{
size_t max_zopfli_len = MaxZopfliLen(params_);
ZopfliCostModel model;
StartPosQueue queue;
BackwardMatch * matches = stackalloc BackwardMatch[MAX_NUM_MATCHES_H10];
HashToBinaryTreeH10 h10 = (HashToBinaryTreeH10)kHashers[10];
size_t store_end = num_bytes >= h10.StoreLookahead()
? position + num_bytes - h10.StoreLookahead() + 1
: position;
size_t i;
nodes[0].length = 0;
nodes[0].u.cost = 0;
InitZopfliCostModel(ref m, &model, num_bytes);
ZopfliCostModelSetFromLiteralCosts(
&model, position, ringbuffer, ringbuffer_mask);
InitStartPosQueue(&queue);
for (i = 0; i + h10.HashTypeLength() - 1 < num_bytes; i++)
{
size_t pos = position + i;
size_t max_distance = Math.Min(pos, max_backward_limit);
size_t num_matches = HashToBinaryTreeH10.FindAllMatches(hasher, ringbuffer,
ringbuffer_mask, pos, num_bytes - i, max_distance, params_, matches);
size_t skip;
if (num_matches > 0 &&
BackwardMatchLength(&matches[num_matches - 1]) > max_zopfli_len)
{
matches[0] = matches[num_matches - 1];
num_matches = 1;
}
skip = UpdateNodes(num_bytes, position, i, ringbuffer, ringbuffer_mask,
params_, max_backward_limit, dist_cache, num_matches, matches, &model,
&queue, nodes);
if (skip < BROTLI_LONG_COPY_QUICK_STEP)
{
skip = 0;
}
if (num_matches == 1 && BackwardMatchLength(&matches[0]) > max_zopfli_len)
{
skip = Math.Max(BackwardMatchLength(&matches[0]), skip);
}
if (skip > 1)
{
/* Add the tail of the copy to the hasher. */
h10.StoreRange(hasher, ringbuffer, ringbuffer_mask, pos + 1, Math.Min(
pos + skip, store_end));
skip--;
while (skip != 0)
{
i++;
if (i + h10.HashTypeLength() - 1 >= num_bytes)
{
break;
}
EvaluateNode(
position, i, max_backward_limit, dist_cache, &model, &queue, nodes);
skip--;
}
}
}
CleanupZopfliCostModel(ref m, &model);
return(ComputeShortestPathFromNodes(num_bytes, nodes));
}
/* Returns longest copy length. */
private static unsafe size_t UpdateNodes(
size_t num_bytes, size_t block_start, size_t pos,
byte *ringbuffer, size_t ringbuffer_mask,
BrotliEncoderParams *params_, size_t max_backward_limit,
int *starting_dist_cache, size_t num_matches,
BackwardMatch *matches, ZopfliCostModel *model,
StartPosQueue *queue, ZopfliNode *nodes)
{
size_t cur_ix = block_start + pos;
size_t cur_ix_masked = cur_ix & ringbuffer_mask;
size_t max_distance = Math.Min(cur_ix, max_backward_limit);
size_t max_len = num_bytes - pos;
size_t max_zopfli_len = MaxZopfliLen(params_);
size_t max_iters = MaxZopfliCandidates(params_);
size_t min_len;
size_t result = 0;
size_t k;
EvaluateNode(block_start, pos, max_backward_limit, starting_dist_cache, model,
queue, nodes);
{
PosData *posdata = StartPosQueueAt(queue, 0);
float min_cost = (posdata->cost + ZopfliCostModelGetMinCostCmd(model) +
ZopfliCostModelGetLiteralCosts(model, posdata->pos, pos));
min_len = ComputeMinimumCopyLength(min_cost, nodes, num_bytes, pos);
}
/* Go over the command starting positions in order of increasing cost
* difference. */
for (k = 0; k < max_iters && k < StartPosQueueSize(queue); ++k)
{
PosData *posdata = StartPosQueueAt(queue, k);
size_t start = posdata->pos;
ushort inscode = GetInsertLengthCode(pos - start);
float start_costdiff = posdata->costdiff;
float base_cost = start_costdiff + (float)GetInsertExtra(inscode) +
ZopfliCostModelGetLiteralCosts(model, 0, pos);
/* Look for last distance matches using the distance cache from this
* starting position. */
size_t best_len = min_len - 1;
size_t j = 0;
for (; j < BROTLI_NUM_DISTANCE_SHORT_CODES && best_len < max_len; ++j)
{
size_t idx = kDistanceCacheIndex[j];
size_t backward =
(size_t)(posdata->distance_cache[idx] + kDistanceCacheOffset[j]);
size_t prev_ix = cur_ix - backward;
if (prev_ix >= cur_ix)
{
continue;
}
if ((backward > max_distance))
{
continue;
}
prev_ix &= ringbuffer_mask;
if (cur_ix_masked + best_len > ringbuffer_mask ||
prev_ix + best_len > ringbuffer_mask ||
ringbuffer[cur_ix_masked + best_len] !=
ringbuffer[prev_ix + best_len])
{
continue;
}
{
size_t len =
FindMatchLengthWithLimit(&ringbuffer[prev_ix],
&ringbuffer[cur_ix_masked],
max_len);
float dist_cost = base_cost +
ZopfliCostModelGetDistanceCost(model, j);
size_t l;
for (l = best_len + 1; l <= len; ++l)
{
ushort copycode = GetCopyLengthCode(l);
ushort cmdcode =
CombineLengthCodes(inscode, copycode, j == 0);
float cost = (cmdcode < 128 ? base_cost : dist_cost) +
(float)GetCopyExtra(copycode) +
ZopfliCostModelGetCommandCost(model, cmdcode);
if (cost < nodes[pos + l].u.cost)
{
UpdateZopfliNode(nodes, pos, start, l, l, backward, j + 1, cost);
result = Math.Max(result, l);
}
best_len = l;
}
}
}
/* At higher iterations look only for new last distance matches, since
* looking only for new command start positions with the same distances
* does not help much. */
if (k >= 2)
{
continue;
}
{
/* Loop through all possible copy lengths at this position. */
size_t len = min_len;
for (j = 0; j < num_matches; ++j)
{
BackwardMatch match = matches[j];
size_t dist = match.distance;
bool is_dictionary_match = (dist > max_distance);
/* We already tried all possible last distance matches, so we can use
* normal distance code here. */
size_t dist_code = dist + BROTLI_NUM_DISTANCE_SHORT_CODES - 1;
ushort dist_symbol;
uint distextra;
uint distnumextra;
float dist_cost;
size_t max_match_len;
PrefixEncodeCopyDistance(dist_code, 0, 0, &dist_symbol, &distextra);
distnumextra = distextra >> 24;
dist_cost = base_cost + (float)distnumextra +
ZopfliCostModelGetDistanceCost(model, dist_symbol);
/* Try all copy lengths up until the maximum copy length corresponding
* to this distance. If the distance refers to the private static unsafe dictionary, or
* the maximum length is long enough, try only one maximum length. */
max_match_len = BackwardMatchLength(&match);
if (len < max_match_len &&
(is_dictionary_match || max_match_len > max_zopfli_len))
{
len = max_match_len;
}
for (; len <= max_match_len; ++len)
{
size_t len_code =
is_dictionary_match ? BackwardMatchLengthCode(&match) : len;
ushort copycode = GetCopyLengthCode(len_code);
ushort cmdcode = CombineLengthCodes(inscode, copycode, false);
float cost = dist_cost + (float)GetCopyExtra(copycode) +
ZopfliCostModelGetCommandCost(model, cmdcode);
if (cost < nodes[pos + len].u.cost)
{
UpdateZopfliNode(nodes, pos, start, len, len_code, dist, 0, cost);
result = Math.Max(result, len);
}
}
}
}
}
return(result);
}
private static unsafe uint ZopfliNodeCommandLength(ZopfliNode *self)
{
return(ZopfliNodeCopyLength(self) + self->insert_length);
}
private static unsafe uint ZopfliNodeCopyDistance(ZopfliNode *self)
{
return(self->distance & 0x1ffffff);
}
private static unsafe uint ZopfliNodeLengthCode(ZopfliNode *self)
{
uint modifier = self->length >> 24;
return(ZopfliNodeCopyLength(self) + 9u - modifier);
}
private static unsafe uint ZopfliNodeCopyLength(ZopfliNode *self)
{
return(self->length & 0xffffff);
}