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re-introduce some comments in Huffman Cost.

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Change-Id: I2396bbc58628dd12a2d36068f7193e2a6eb4d166
This commit is contained in:
Vincent Rabaud 2017-01-06 13:17:14 +01:00
parent 259e98286a
commit ecff04f625
1 changed files with 9 additions and 0 deletions
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9
src/enc/histogram.c
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@ -214,10 +214,19 @@ static double InitialHuffmanCost(void) {
// Finalize the Huffman cost based on streak numbers and length type (<3 or >=3) // Finalize the Huffman cost based on streak numbers and length type (<3 or >=3)
static double FinalHuffmanCost(const VP8LStreaks* const stats) { static double FinalHuffmanCost(const VP8LStreaks* const stats) {
// The constants in this function are experimental and got rounded from
// their original values in 1/8 when switched to 1/1024.
double retval = InitialHuffmanCost(); double retval = InitialHuffmanCost();
// Second coefficient: Many zeros in the histogram are covered efficiently
// by a run-length encode. Originally 2/8.
retval += stats->counts[0] * 1.5625 + 0.234375 * stats->streaks[0][1]; retval += stats->counts[0] * 1.5625 + 0.234375 * stats->streaks[0][1];
// Second coefficient: Constant values are encoded less efficiently, but still
// RLE'ed. Originally 6/8.
retval += stats->counts[1] * 2.578125 + 0.703125 * stats->streaks[1][1]; retval += stats->counts[1] * 2.578125 + 0.703125 * stats->streaks[1][1];
// 0s are usually encoded more efficiently than non-0s.
// Originally 15/8.
retval += 1.796875 * stats->streaks[0][0]; retval += 1.796875 * stats->streaks[0][0];
// Originally 26/8.
retval += 3.28125 * stats->streaks[1][0]; retval += 3.28125 * stats->streaks[1][0];
return retval; return retval;
} }