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Create LUT for PrefixEncode.

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This speeds up lossless compression by 5%.
Change-Id: Ifd114b1d9850dc3aac74593809e7d48529d35e3d
This commit is contained in:
Vikas Arora
2013-08-05 10:19:24 -07:00
parent 988b70844e
commit 69257f70df
6 changed files with 191 additions and 80 deletions
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12
src/enc/backward_references.c
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@ -462,16 +462,16 @@ static WEBP_INLINE double GetCacheCost(const CostModel* const m, uint32_t idx) {
static WEBP_INLINE double GetLengthCost(const CostModel* const m,
uint32_t length) {
int code, extra_bits_count, extra_bits_value;
PrefixEncode(length, &code, &extra_bits_count, &extra_bits_value);
return m->literal_[VALUES_IN_BYTE + code] + extra_bits_count;
int code, extra_bits, extra_bits_val;
VP8LPrefixEncode(length, &code, &extra_bits, &extra_bits_val);
return m->literal_[VALUES_IN_BYTE + code] + extra_bits;
}
static WEBP_INLINE double GetDistanceCost(const CostModel* const m,
uint32_t distance) {
int code, extra_bits_count, extra_bits_value;
PrefixEncode(distance, &code, &extra_bits_count, &extra_bits_value);
return m->distance_[code] + extra_bits_count;
int code, extra_bits, extra_bits_val;
VP8LPrefixEncode(distance, &code, &extra_bits, &extra_bits_val);
return m->distance_[code] + extra_bits;
}
static int BackwardReferencesHashChainDistanceOnly(

67
src/enc/backward_references.h
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@ -30,73 +30,6 @@ extern "C" {
#define PIX_OR_COPY_CODES_MAX \
(NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS))
// -----------------------------------------------------------------------------
// PrefixEncode()
// use GNU builtins where available.
#if defined(__GNUC__) && \
((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
assert(n != 0);
return 31 ^ __builtin_clz(n);
}
#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86))
#include <intrin.h>
#pragma intrinsic(_BitScanReverse)
static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
unsigned long first_set_bit;
assert(n != 0);
_BitScanReverse(&first_set_bit, n);
return first_set_bit;
}
#else
// Returns (int)floor(log2(n)). n must be > 0.
static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
int log = 0;
uint32_t value = n;
int i;
assert(n != 0);
for (i = 4; i >= 0; --i) {
const int shift = (1 << i);
const uint32_t x = value >> shift;
if (x != 0) {
value = x;
log += shift;
}
}
return log;
}
#endif
static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) {
const int log_floor = BitsLog2Floor(n);
if (n == (n & ~(n - 1))) // zero or a power of two.
return log_floor;
else
return log_floor + 1;
}
// Splitting of distance and length codes into prefixes and
// extra bits. The prefixes are encoded with an entropy code
// while the extra bits are stored just as normal bits.
static WEBP_INLINE void PrefixEncode(int distance, int* const code,
int* const extra_bits_count,
int* const extra_bits_value) {
if (distance > 2) { // Collect the two most significant bits.
const int highest_bit = BitsLog2Floor(--distance);
const int second_highest_bit = (distance >> (highest_bit - 1)) & 1;
*extra_bits_count = highest_bit - 1;
*extra_bits_value = distance & ((1 << *extra_bits_count) - 1);
*code = 2 * highest_bit + second_highest_bit;
} else {
*extra_bits_count = 0;
*extra_bits_value = 0;
*code = (distance == 2) ? 1 : 0;
}
}
// -----------------------------------------------------------------------------
// PixOrCopy

8
src/enc/histogram.c
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@ -90,12 +90,10 @@ void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo,
int literal_ix = 256 + NUM_LENGTH_CODES + PixOrCopyCacheIdx(v);
++histo->literal_[literal_ix];
} else {
int code, extra_bits_count, extra_bits_value;
PrefixEncode(PixOrCopyLength(v),
&code, &extra_bits_count, &extra_bits_value);
int code, extra_bits, extra_bits_val;
VP8LPrefixEncode(PixOrCopyLength(v), &code, &extra_bits, &extra_bits_val);
++histo->literal_[256 + code];
PrefixEncode(PixOrCopyDistance(v),
&code, &extra_bits_count, &extra_bits_value);
VP8LPrefixEncode(PixOrCopyDistance(v), &code, &extra_bits, &extra_bits_val);
++histo->distance_[code];
}
}

4
src/enc/vp8l.c
View File

@ -448,12 +448,12 @@ static void StoreImageToBitMask(
int bits, n_bits;
int code, distance;
PrefixEncode(v->len, &code, &n_bits, &bits);
VP8LPrefixEncode(v->len, &code, &n_bits, &bits);
WriteHuffmanCode(bw, codes, 256 + code);
VP8LWriteBits(bw, n_bits, bits);
distance = PixOrCopyDistance(v);
PrefixEncode(distance, &code, &n_bits, &bits);
VP8LPrefixEncode(distance, &code, &n_bits, &bits);
WriteHuffmanCode(bw, codes + 4, code);
VP8LWriteBits(bw, n_bits, bits);
}