/* What is the bit cost of moving histogram from cur_symbol to candidate. */
public static double BrotliHistogramBitCostDistance(
HistogramLiteral *histogram, HistogramLiteral *candidate)
{
if (histogram->total_count_ == 0)
{
return(0.0);
}
else
{
HistogramLiteral tmp = *histogram;
HistogramLiteral.HistogramAddHistogram(&tmp, candidate);
return(BitCostLiteral.BrotliPopulationCost(&tmp) - candidate->bit_cost_);
}
}
public static void BrotliCompareAndPushToQueue(
HistogramLiteral *out_, uint *cluster_size, uint idx1,
uint idx2, size_t max_num_pairs, HistogramPair *pairs,
size_t *num_pairs)
{
bool is_good_pair = false;
HistogramPair p = new HistogramPair();
if (idx1 == idx2)
{
return;
}
if (idx2 < idx1)
{
uint t = idx2;
idx2 = idx1;
idx1 = t;
}
p.idx1 = idx1;
p.idx2 = idx2;
p.cost_diff = 0.5 * ClusterCostDiff(cluster_size[idx1], cluster_size[idx2]);
p.cost_diff -= out_[idx1].bit_cost_;
p.cost_diff -= out_[idx2].bit_cost_;
if (out_[idx1].total_count_ == 0)
{
p.cost_combo = out_[idx2].bit_cost_;
is_good_pair = true;
}
else if (out_[idx2].total_count_ == 0)
{
p.cost_combo = out_[idx1].bit_cost_;
is_good_pair = true;
}
else
{
double threshold = *num_pairs == 0 ? 1e99 : Math.Max(0.0, pairs[0].cost_diff);
HistogramLiteral combo = out_[idx1];
double cost_combo;
HistogramLiteral.HistogramAddHistogram(&combo, &out_[idx2]);
cost_combo = BitCostLiteral.BrotliPopulationCost(&combo);
if (cost_combo < threshold - p.cost_diff)
{
p.cost_combo = cost_combo;
is_good_pair = true;
}
}
if (is_good_pair)
{
p.cost_diff += p.cost_combo;
if (*num_pairs > 0 && HistogramPairIsLess(&pairs[0], &p))
{
/* Replace the top of the queue if needed. */
if (*num_pairs < max_num_pairs)
{
pairs[*num_pairs] = pairs[0];
++(*num_pairs);
}
pairs[0] = p;
}
else if (*num_pairs < max_num_pairs)
{
pairs[*num_pairs] = p;
++(*num_pairs);
}
}
}
public static void BrotliClusterHistograms(
ref MemoryManager m, HistogramLiteral *in_, size_t in_size,
size_t max_histograms, HistogramLiteral *out_, size_t *out_size,
uint *histogram_symbols)
{
uint * cluster_size = (uint *)BrotliAllocate(ref m, in_size * sizeof(uint));
uint * clusters = (uint *)BrotliAllocate(ref m, in_size * sizeof(uint));
size_t num_clusters = 0;
size_t max_input_histograms = 64;
size_t pairs_capacity = max_input_histograms * max_input_histograms / 2;
/* For the first pass of clustering, we allow all pairs. */
HistogramPair *pairs =
(HistogramPair *)BrotliAllocate(ref m, (pairs_capacity + 1) * sizeof(HistogramPair));
size_t i;
for (i = 0; i < in_size; ++i)
{
cluster_size[i] = 1;
}
for (i = 0; i < in_size; ++i)
{
out_[i] = in_[i];
out_[i].bit_cost_ = BitCostLiteral.BrotliPopulationCost(&in_[i]);
histogram_symbols[i] = (uint)i;
}
for (i = 0; i < in_size; i += max_input_histograms)
{
size_t num_to_combine =
Math.Min(in_size - i, max_input_histograms);
size_t num_new_clusters;
size_t j;
for (j = 0; j < num_to_combine; ++j)
{
clusters[num_clusters + j] = (uint)(i + j);
}
num_new_clusters =
BrotliHistogramCombine(out_, cluster_size,
&histogram_symbols[i],
&clusters[num_clusters], pairs,
num_to_combine, num_to_combine,
max_histograms, pairs_capacity);
num_clusters += num_new_clusters;
}
{
/* For the second pass, we limit the total number of histogram pairs.
* After this limit is reached, we only keep searching for the best pair. */
size_t max_num_pairs = Math.Min(
64 * num_clusters, (num_clusters / 2) * num_clusters);
BrotliEnsureCapacity(ref m, sizeof(HistogramPair), (void **)&pairs, &pairs_capacity, max_num_pairs + 1);
/* Collapse similar histograms. */
num_clusters = BrotliHistogramCombine(out_, cluster_size,
histogram_symbols, clusters,
pairs, num_clusters, in_size,
max_histograms, max_num_pairs);
}
BrotliFree(ref m, pairs);
BrotliFree(ref m, cluster_size);
/* Find the optimal map from original histograms to the final ones. */
BrotliHistogramRemap(in_, in_size, clusters, num_clusters,
out_, histogram_symbols);
BrotliFree(ref m, clusters);
/* Convert the context map to a canonical form. */
*out_size = BrotliHistogramReindex(ref m, out_, histogram_symbols, in_size);
}
