mirror of
https://github.com/webmproject/libwebp.git
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28c37ebd5a
was only used once. Better fall back for Log2Floor. Change-Id: Ibcc26505440971bffe62ba6aca3d179ca85791d4
203 lines
7.8 KiB
C
203 lines
7.8 KiB
C
// Copyright 2012 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Image transforms and color space conversion methods for lossless decoder.
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//
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// Authors: Vikas Arora (vikaas.arora@gmail.com)
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// Jyrki Alakuijala (jyrki@google.com)
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// Vincent Rabaud (vrabaud@google.com)
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#ifndef WEBP_DSP_LOSSLESS_COMMON_H_
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#define WEBP_DSP_LOSSLESS_COMMON_H_
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#include "../webp/types.h"
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#include "../utils/utils.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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//------------------------------------------------------------------------------
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// Decoding
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// color mapping related functions.
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static WEBP_INLINE uint32_t VP8GetARGBIndex(uint32_t idx) {
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return (idx >> 8) & 0xff;
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}
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static WEBP_INLINE uint8_t VP8GetAlphaIndex(uint8_t idx) {
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return idx;
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}
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static WEBP_INLINE uint32_t VP8GetARGBValue(uint32_t val) {
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return val;
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}
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static WEBP_INLINE uint8_t VP8GetAlphaValue(uint32_t val) {
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return (val >> 8) & 0xff;
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}
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//------------------------------------------------------------------------------
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// Misc methods.
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// Computes sampled size of 'size' when sampling using 'sampling bits'.
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static WEBP_INLINE uint32_t VP8LSubSampleSize(uint32_t size,
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uint32_t sampling_bits) {
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return (size + (1 << sampling_bits) - 1) >> sampling_bits;
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}
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// Converts near lossless quality into max number of bits shaved off.
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static WEBP_INLINE int VP8LNearLosslessBits(int near_lossless_quality) {
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// 100 -> 0
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// 80..99 -> 1
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// 60..79 -> 2
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// 40..59 -> 3
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// 20..39 -> 4
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// 0..19 -> 5
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return 5 - near_lossless_quality / 20;
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}
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// -----------------------------------------------------------------------------
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// Faster logarithm for integers. Small values use a look-up table.
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// The threshold till approximate version of log_2 can be used.
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// Practically, we can get rid of the call to log() as the two values match to
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// very high degree (the ratio of these two is 0.99999x).
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// Keeping a high threshold for now.
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#define APPROX_LOG_WITH_CORRECTION_MAX 65536
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#define APPROX_LOG_MAX 4096
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#define LOG_2_RECIPROCAL 1.44269504088896338700465094007086
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#define LOG_LOOKUP_IDX_MAX 256
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extern const float kLog2Table[LOG_LOOKUP_IDX_MAX];
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extern const float kSLog2Table[LOG_LOOKUP_IDX_MAX];
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typedef float (*VP8LFastLog2SlowFunc)(uint32_t v);
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extern VP8LFastLog2SlowFunc VP8LFastLog2Slow;
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extern VP8LFastLog2SlowFunc VP8LFastSLog2Slow;
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static WEBP_INLINE float VP8LFastLog2(uint32_t v) {
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return (v < LOG_LOOKUP_IDX_MAX) ? kLog2Table[v] : VP8LFastLog2Slow(v);
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}
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// Fast calculation of v * log2(v) for integer input.
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static WEBP_INLINE float VP8LFastSLog2(uint32_t v) {
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return (v < LOG_LOOKUP_IDX_MAX) ? kSLog2Table[v] : VP8LFastSLog2Slow(v);
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}
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// -----------------------------------------------------------------------------
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// PrefixEncode()
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// Splitting of distance and length codes into prefixes and
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// extra bits. The prefixes are encoded with an entropy code
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// while the extra bits are stored just as normal bits.
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static WEBP_INLINE void VP8LPrefixEncodeBitsNoLUT(int distance, int* const code,
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int* const extra_bits) {
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const int highest_bit = BitsLog2Floor(--distance);
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const int second_highest_bit = (distance >> (highest_bit - 1)) & 1;
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*extra_bits = highest_bit - 1;
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*code = 2 * highest_bit + second_highest_bit;
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}
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static WEBP_INLINE void VP8LPrefixEncodeNoLUT(int distance, int* const code,
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int* const extra_bits,
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int* const extra_bits_value) {
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const int highest_bit = BitsLog2Floor(--distance);
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const int second_highest_bit = (distance >> (highest_bit - 1)) & 1;
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*extra_bits = highest_bit - 1;
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*extra_bits_value = distance & ((1 << *extra_bits) - 1);
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*code = 2 * highest_bit + second_highest_bit;
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}
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#define PREFIX_LOOKUP_IDX_MAX 512
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typedef struct {
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int8_t code_;
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int8_t extra_bits_;
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} VP8LPrefixCode;
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// These tables are derived using VP8LPrefixEncodeNoLUT.
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extern const VP8LPrefixCode kPrefixEncodeCode[PREFIX_LOOKUP_IDX_MAX];
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extern const uint8_t kPrefixEncodeExtraBitsValue[PREFIX_LOOKUP_IDX_MAX];
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static WEBP_INLINE void VP8LPrefixEncodeBits(int distance, int* const code,
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int* const extra_bits) {
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if (distance < PREFIX_LOOKUP_IDX_MAX) {
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const VP8LPrefixCode prefix_code = kPrefixEncodeCode[distance];
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*code = prefix_code.code_;
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*extra_bits = prefix_code.extra_bits_;
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} else {
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VP8LPrefixEncodeBitsNoLUT(distance, code, extra_bits);
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}
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}
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static WEBP_INLINE void VP8LPrefixEncode(int distance, int* const code,
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int* const extra_bits,
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int* const extra_bits_value) {
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if (distance < PREFIX_LOOKUP_IDX_MAX) {
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const VP8LPrefixCode prefix_code = kPrefixEncodeCode[distance];
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*code = prefix_code.code_;
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*extra_bits = prefix_code.extra_bits_;
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*extra_bits_value = kPrefixEncodeExtraBitsValue[distance];
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} else {
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VP8LPrefixEncodeNoLUT(distance, code, extra_bits, extra_bits_value);
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}
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}
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// Sum of each component, mod 256.
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static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE
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uint32_t VP8LAddPixels(uint32_t a, uint32_t b) {
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const uint32_t alpha_and_green = (a & 0xff00ff00u) + (b & 0xff00ff00u);
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const uint32_t red_and_blue = (a & 0x00ff00ffu) + (b & 0x00ff00ffu);
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return (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu);
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}
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// Difference of each component, mod 256.
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static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE
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uint32_t VP8LSubPixels(uint32_t a, uint32_t b) {
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const uint32_t alpha_and_green =
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0x00ff00ffu + (a & 0xff00ff00u) - (b & 0xff00ff00u);
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const uint32_t red_and_blue =
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0xff00ff00u + (a & 0x00ff00ffu) - (b & 0x00ff00ffu);
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return (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu);
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}
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//------------------------------------------------------------------------------
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// Transform-related functions use din both encoding and decoding.
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// Macros used to create a batch predictor that iteratively uses a
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// one-pixel predictor.
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// The predictor is added to the output pixel (which
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// is therefore considered as a residual) to get the final prediction.
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#define GENERATE_PREDICTOR_ADD(PREDICTOR, PREDICTOR_ADD) \
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static void PREDICTOR_ADD(const uint32_t* in, const uint32_t* upper, \
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int num_pixels, uint32_t* out) { \
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int x; \
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for (x = 0; x < num_pixels; ++x) { \
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const uint32_t pred = (PREDICTOR)(out[x - 1], upper + x); \
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out[x] = VP8LAddPixels(in[x], pred); \
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} \
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}
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// It subtracts the prediction from the input pixel and stores the residual
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// in the output pixel.
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#define GENERATE_PREDICTOR_SUB(PREDICTOR, PREDICTOR_SUB) \
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static void PREDICTOR_SUB(const uint32_t* in, const uint32_t* upper, \
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int num_pixels, uint32_t* out) { \
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int x; \
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for (x = 0; x < num_pixels; ++x) { \
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const uint32_t pred = (PREDICTOR)(in[x - 1], upper + x); \
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out[x] = VP8LSubPixels(in[x], pred); \
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} \
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}
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#ifdef __cplusplus
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} // extern "C"
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#endif
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#endif // WEBP_DSP_LOSSLESS_COMMON_H_
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