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Convert VP8LFastLog2 to fixed point

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The lossless encoding speed-ups are:
- up to 1% with default parameters
- up to 4% in cruncher mode: -q 100 -m 6

Change-Id: Id92d4bad0b0a2c28c8aa9ff5280eea5717017f30
This commit is contained in:
Vincent Rabaud
2024-06-26 15:21:55 +02:00
parent c4af79d053
commit 0a9f1c19f8
5 changed files with 154 additions and 81 deletions
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29
src/dsp/lossless_common.h
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@ -73,16 +73,29 @@ static WEBP_INLINE int VP8LNearLosslessBits(int near_lossless_quality) {
// Keeping a high threshold for now.
#define APPROX_LOG_WITH_CORRECTION_MAX 65536
#define APPROX_LOG_MAX 4096
// VP8LFastLog2 and VP8LFastSLog2 are used on elements from image histograms.
// The histogram values cannot exceed the maximum number of pixels, which
// is (1 << 14) * (1 << 14). Therefore S * log(S) < (1 << 33).
// No more than 32 bits of precision should be chosen.
// To match the original float implementation, 23 bits of precision are used.
#define LOG_2_PRECISION_BITS 23
#define LOG_2_RECIPROCAL 1.44269504088896338700465094007086
// LOG_2_RECIPROCAL * (1 << LOG_2_PRECISION_BITS)
#define LOG_2_RECIPROCAL_FIXED_DOUBLE 12102203.161561485379934310913085937500
#define LOG_2_RECIPROCAL_FIXED 12102203
#define LOG_LOOKUP_IDX_MAX 256
extern const float kLog2Table[LOG_LOOKUP_IDX_MAX];
extern const uint32_t kLog2Table[LOG_LOOKUP_IDX_MAX];
extern const float kSLog2Table[LOG_LOOKUP_IDX_MAX];
typedef float (*VP8LFastLog2SlowFunc)(uint32_t v);
// TODO(vrabaud) remove this table once VP8LFastSLog2 is switched to fixed
// point.
extern const float kLog2fTable[LOG_LOOKUP_IDX_MAX];
typedef uint32_t (*VP8LFastLog2SlowFunc)(uint32_t v);
typedef float (*VP8LFastSLog2SlowFunc)(uint32_t v);
extern VP8LFastLog2SlowFunc VP8LFastLog2Slow;
extern VP8LFastLog2SlowFunc VP8LFastSLog2Slow;
extern VP8LFastSLog2SlowFunc VP8LFastSLog2Slow;
static WEBP_INLINE float VP8LFastLog2(uint32_t v) {
static WEBP_INLINE uint32_t VP8LFastLog2(uint32_t v) {
return (v < LOG_LOOKUP_IDX_MAX) ? kLog2Table[v] : VP8LFastLog2Slow(v);
}
// Fast calculation of v * log2(v) for integer input.
@ -90,6 +103,14 @@ static WEBP_INLINE float VP8LFastSLog2(uint32_t v) {
return (v < LOG_LOOKUP_IDX_MAX) ? kSLog2Table[v] : VP8LFastSLog2Slow(v);
}
static WEBP_INLINE uint64_t RightShiftRound(uint64_t v, uint32_t shift) {
return (v + (1ull << shift >> 1)) >> shift;
}
static WEBP_INLINE int64_t DivRound(int64_t a, int64_t b) {
return ((a < 0) == (b < 0)) ? ((a + b / 2) / b) : ((a - b / 2) / b);
}
// -----------------------------------------------------------------------------
// PrefixEncode()