text: // Copyright 2011 Google Inc. All Rights Reserved.
  //
  // Use of this source code is governed by a BSD-style license
  // that can be found in the COPYING file in the root of the source
  // tree. An additional intellectual property rights grant can be found
  // in the file PATENTS. All contributing project authors may
  // be found in the AUTHORS file in the root of the source tree.
  // -----------------------------------------------------------------------------
  //
  //   Speed-critical functions.
  //
  // Author: Skal (pascal.massimino@gmail.com)
  
  #ifndef WEBP_DSP_DSP_H_
  #define WEBP_DSP_DSP_H_
  
  #ifdef HAVE_CONFIG_H
  #include "src/webp/config.h"
  #endif
  
  #include "src/webp/types.h"
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #define BPS 32   // this is the common stride for enc/dec
  
  //------------------------------------------------------------------------------
  // CPU detection
  
  #if defined(__GNUC__)
  # define LOCAL_GCC_VERSION ((__GNUC__ << 8) | __GNUC_MINOR__)
  # define LOCAL_GCC_PREREQ(maj, min) \
      (LOCAL_GCC_VERSION >= (((maj) << 8) | (min)))
  #else
  # define LOCAL_GCC_VERSION 0
  # define LOCAL_GCC_PREREQ(maj, min) 0
  #endif
  
  #if defined(__clang__)
  # define LOCAL_CLANG_VERSION ((__clang_major__ << 8) | __clang_minor__)
  # define LOCAL_CLANG_PREREQ(maj, min) \
      (LOCAL_CLANG_VERSION >= (((maj) << 8) | (min)))
  #else
  # define LOCAL_CLANG_VERSION 0
  # define LOCAL_CLANG_PREREQ(maj, min) 0
  #endif
  
  #ifndef __has_builtin
  # define __has_builtin(x) 0
  #endif
  
  #if defined(_MSC_VER) && _MSC_VER > 1310 && \
      (defined(_M_X64) || defined(_M_IX86))
  #define WEBP_MSC_SSE2  // Visual C++ SSE2 targets
  #endif
  
  #if defined(_MSC_VER) && _MSC_VER >= 1500 && \
      (defined(_M_X64) || defined(_M_IX86))
  #define WEBP_MSC_SSE41  // Visual C++ SSE4.1 targets
  #endif
  
  // WEBP_HAVE_* are used to indicate the presence of the instruction set in dsp
  // files without intrinsics, allowing the corresponding Init() to be called.
  // Files containing intrinsics will need to be built targeting the instruction
  // set so should succeed on one of the earlier tests.
  #if defined(__SSE2__) || defined(WEBP_MSC_SSE2) || defined(WEBP_HAVE_SSE2)
  #define WEBP_USE_SSE2
  #endif
  
  #if defined(__SSE4_1__) || defined(WEBP_MSC_SSE41) || defined(WEBP_HAVE_SSE41)
  #define WEBP_USE_SSE41
  #endif
  
  // The intrinsics currently cause compiler errors with arm-nacl-gcc and the
  // inline assembly would need to be modified for use with Native Client.
  #if (defined(__ARM_NEON__) || \
       defined(__aarch64__) || defined(WEBP_HAVE_NEON)) && \
      !defined(__native_client__)
  #define WEBP_USE_NEON
  #endif
  
  #if !defined(WEBP_USE_NEON) && defined(__ANDROID__) && \
      defined(__ARM_ARCH_7A__) && defined(HAVE_CPU_FEATURES_H)
  #define WEBP_ANDROID_NEON  // Android targets that may have NEON
  #define WEBP_USE_NEON
  #endif
  
  #if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_M_ARM)
  #define WEBP_USE_NEON
  #define WEBP_USE_INTRINSICS
  #endif
  
  #if defined(__mips__) && !defined(__mips64) && \
      defined(__mips_isa_rev) && (__mips_isa_rev >= 1) && (__mips_isa_rev < 6)
  #define WEBP_USE_MIPS32
  #if (__mips_isa_rev >= 2)
  #define WEBP_USE_MIPS32_R2
  #if defined(__mips_dspr2) || (defined(__mips_dsp_rev) && __mips_dsp_rev >= 2)
  #define WEBP_USE_MIPS_DSP_R2
  #endif
  #endif
  #endif
  
  #if defined(__mips_msa) && defined(__mips_isa_rev) && (__mips_isa_rev >= 5)
  #define WEBP_USE_MSA
  #endif
  
  #ifndef WEBP_DSP_OMIT_C_CODE
  #define WEBP_DSP_OMIT_C_CODE 1
  #endif
  
  #if (defined(__aarch64__) || defined(__ARM_NEON__)) && WEBP_DSP_OMIT_C_CODE
  #define WEBP_NEON_OMIT_C_CODE 1
  #else
  #define WEBP_NEON_OMIT_C_CODE 0
  #endif
  
  #if !(LOCAL_CLANG_PREREQ(3,8) || LOCAL_GCC_PREREQ(4,8) || defined(__aarch64__))
  #define WEBP_NEON_WORK_AROUND_GCC 1
  #else
  #define WEBP_NEON_WORK_AROUND_GCC 0
  #endif
  
  // This macro prevents thread_sanitizer from reporting known concurrent writes.
  #define WEBP_TSAN_IGNORE_FUNCTION
  #if defined(__has_feature)
  #if __has_feature(thread_sanitizer)
  #undef WEBP_TSAN_IGNORE_FUNCTION
  #define WEBP_TSAN_IGNORE_FUNCTION __attribute__((no_sanitize_thread))
  #endif
  #endif
  
  #if defined(WEBP_USE_THREAD) && !defined(_WIN32)
  #include <pthread.h>  // NOLINT
  
  #define WEBP_DSP_INIT(func) do {                                    \
    static volatile VP8CPUInfo func ## _last_cpuinfo_used =           \
        (VP8CPUInfo)&func ## _last_cpuinfo_used;                      \
    static pthread_mutex_t func ## _lock = PTHREAD_MUTEX_INITIALIZER; \
    if (pthread_mutex_lock(&func ## _lock)) break;                    \
    if (func ## _last_cpuinfo_used != VP8GetCPUInfo) func();          \
    func ## _last_cpuinfo_used = VP8GetCPUInfo;                       \
    (void)pthread_mutex_unlock(&func ## _lock);                       \
  } while (0)
  #else  // !(defined(WEBP_USE_THREAD) && !defined(_WIN32))
  #define WEBP_DSP_INIT(func) do {                                    \
    static volatile VP8CPUInfo func ## _last_cpuinfo_used =           \
        (VP8CPUInfo)&func ## _last_cpuinfo_used;                      \
    if (func ## _last_cpuinfo_used == VP8GetCPUInfo) break;           \
    func();                                                           \
    func ## _last_cpuinfo_used = VP8GetCPUInfo;                       \
  } while (0)
  #endif  // defined(WEBP_USE_THREAD) && !defined(_WIN32)
  
  // Defines an Init + helper function that control multiple initialization of
  // function pointers / tables.
  /* Usage:
     WEBP_DSP_INIT_FUNC(InitFunc) {
       ...function body
     }
  */
  #define WEBP_DSP_INIT_FUNC(name)                             \
    static WEBP_TSAN_IGNORE_FUNCTION void name ## _body(void); \
    WEBP_TSAN_IGNORE_FUNCTION void name(void) {                \
      WEBP_DSP_INIT(name ## _body);                            \
    }                                                          \
    static WEBP_TSAN_IGNORE_FUNCTION void name ## _body(void)
  
  #define WEBP_UBSAN_IGNORE_UNDEF
  #define WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW
  #if defined(__clang__) && defined(__has_attribute)
  #if __has_attribute(no_sanitize)
  // This macro prevents the undefined behavior sanitizer from reporting
  // failures. This is only meant to silence unaligned loads on platforms that
  // are known to support them.
  #undef WEBP_UBSAN_IGNORE_UNDEF
  #define WEBP_UBSAN_IGNORE_UNDEF \
    __attribute__((no_sanitize("undefined")))
  
  // This macro prevents the undefined behavior sanitizer from reporting
  // failures related to unsigned integer overflows. This is only meant to
  // silence cases where this well defined behavior is expected.
  #undef WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW
  #define WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW \
    __attribute__((no_sanitize("unsigned-integer-overflow")))
  #endif
  #endif
  
  // If 'ptr' is NULL, returns NULL. Otherwise returns 'ptr + off'.
  // Prevents undefined behavior sanitizer nullptr-with-nonzero-offset warning.
  #if !defined(WEBP_OFFSET_PTR)
  #define WEBP_OFFSET_PTR(ptr, off) (((ptr) == NULL) ? NULL : ((ptr) + (off)))
  #endif
  
  // Regularize the definition of WEBP_SWAP_16BIT_CSP (backward compatibility)
  #if !defined(WEBP_SWAP_16BIT_CSP)
  #define WEBP_SWAP_16BIT_CSP 0
  #endif
  
  // some endian fix (e.g.: mips-gcc doesn't define __BIG_ENDIAN__)
  #if !defined(WORDS_BIGENDIAN) && \
      (defined(__BIG_ENDIAN__) || defined(_M_PPC) || \
       (defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)))
  #define WORDS_BIGENDIAN
  #endif
  
  typedef enum {
    kSSE2,
    kSSE3,
    kSlowSSSE3,  // special feature for slow SSSE3 architectures
    kSSE4_1,
    kAVX,
    kAVX2,
    kNEON,
    kMIPS32,
    kMIPSdspR2,
    kMSA
  } CPUFeature;
  // returns true if the CPU supports the feature.
  typedef int (*VP8CPUInfo)(CPUFeature feature);
  WEBP_EXTERN VP8CPUInfo VP8GetCPUInfo;
  
  //------------------------------------------------------------------------------
  // Init stub generator
  
  // Defines an init function stub to ensure each module exposes a symbol,
  // avoiding a compiler warning.
  #define WEBP_DSP_INIT_STUB(func) \
    extern void func(void); \
    void func(void) {}
  
  //------------------------------------------------------------------------------
  // Encoding
  
  // Transforms
  // VP8Idct: Does one of two inverse transforms. If do_two is set, the transforms
  //          will be done for (ref, in, dst) and (ref + 4, in + 16, dst + 4).
  typedef void (*VP8Idct)(const uint8_t* ref, const int16_t* in, uint8_t* dst,
                          int do_two);
  typedef void (*VP8Fdct)(const uint8_t* src, const uint8_t* ref, int16_t* out);
  typedef void (*VP8WHT)(const int16_t* in, int16_t* out);
  extern VP8Idct VP8ITransform;
  extern VP8Fdct VP8FTransform;
  extern VP8Fdct VP8FTransform2;   // performs two transforms at a time
  extern VP8WHT VP8FTransformWHT;
  // Predictions
  // *dst is the destination block. *top and *left can be NULL.
  typedef void (*VP8IntraPreds)(uint8_t* dst, const uint8_t* left,
                                const uint8_t* top);
  typedef void (*VP8Intra4Preds)(uint8_t* dst, const uint8_t* top);
  extern VP8Intra4Preds VP8EncPredLuma4;
  extern VP8IntraPreds VP8EncPredLuma16;
  extern VP8IntraPreds VP8EncPredChroma8;
  
  typedef int (*VP8Metric)(const uint8_t* pix, const uint8_t* ref);
  extern VP8Metric VP8SSE16x16, VP8SSE16x8, VP8SSE8x8, VP8SSE4x4;
  typedef int (*VP8WMetric)(const uint8_t* pix, const uint8_t* ref,
                            const uint16_t* const weights);
  // The weights for VP8TDisto4x4 and VP8TDisto16x16 contain a row-major
  // 4 by 4 symmetric matrix.
  extern VP8WMetric VP8TDisto4x4, VP8TDisto16x16;
  
  // Compute the average (DC) of four 4x4 blocks.
  // Each sub-4x4 block #i sum is stored in dc[i].
  typedef void (*VP8MeanMetric)(const uint8_t* ref, uint32_t dc[4]);
  extern VP8MeanMetric VP8Mean16x4;
  
  typedef void (*VP8BlockCopy)(const uint8_t* src, uint8_t* dst);
  extern VP8BlockCopy VP8Copy4x4;
  extern VP8BlockCopy VP8Copy16x8;
  // Quantization
  struct VP8Matrix;   // forward declaration
  typedef int (*VP8QuantizeBlock)(int16_t in[16], int16_t out[16],
                                  const struct VP8Matrix* const mtx);
  // Same as VP8QuantizeBlock, but quantizes two consecutive blocks.
  typedef int (*VP8Quantize2Blocks)(int16_t in[32], int16_t out[32],
                                    const struct VP8Matrix* const mtx);
  
  extern VP8QuantizeBlock VP8EncQuantizeBlock;
  extern VP8Quantize2Blocks VP8EncQuantize2Blocks;
  
  // specific to 2nd transform:
  typedef int (*VP8QuantizeBlockWHT)(int16_t in[16], int16_t out[16],
                                     const struct VP8Matrix* const mtx);
  extern VP8QuantizeBlockWHT VP8EncQuantizeBlockWHT;
  
  extern const int VP8DspScan[16 + 4 + 4];
  
  // Collect histogram for susceptibility calculation.
  #define MAX_COEFF_THRESH   31   // size of histogram used by CollectHistogram.
  typedef struct {
    // We only need to store max_value and last_non_zero, not the distribution.
    int max_value;
    int last_non_zero;
  } VP8Histogram;
  typedef void (*VP8CHisto)(const uint8_t* ref, const uint8_t* pred,
                            int start_block, int end_block,
                            VP8Histogram* const histo);
  extern VP8CHisto VP8CollectHistogram;
  // General-purpose util function to help VP8CollectHistogram().
  void VP8SetHistogramData(const int distribution[MAX_COEFF_THRESH + 1],
                           VP8Histogram* const histo);
  
  // must be called before using any of the above
  void VP8EncDspInit(void);
  
  //------------------------------------------------------------------------------
  // cost functions (encoding)
  
  extern const uint16_t VP8EntropyCost[256];        // 8bit fixed-point log(p)
  // approximate cost per level:
  extern const uint16_t VP8LevelFixedCosts[2047 /*MAX_LEVEL*/ + 1];
  extern const uint8_t VP8EncBands[16 + 1];
  
  struct VP8Residual;
  typedef void (*VP8SetResidualCoeffsFunc)(const int16_t* const coeffs,
                                           struct VP8Residual* const res);
  extern VP8SetResidualCoeffsFunc VP8SetResidualCoeffs;
  
  // Cost calculation function.
  typedef int (*VP8GetResidualCostFunc)(int ctx0,
                                        const struct VP8Residual* const res);
  extern VP8GetResidualCostFunc VP8GetResidualCost;
  
  // must be called before anything using the above
  void VP8EncDspCostInit(void);
  
  //------------------------------------------------------------------------------
  // SSIM / PSNR utils
  
  // struct for accumulating statistical moments
  typedef struct {
    uint32_t w;              // sum(w_i) : sum of weights
    uint32_t xm, ym;         // sum(w_i * x_i), sum(w_i * y_i)
    uint32_t xxm, xym, yym;  // sum(w_i * x_i * x_i), etc.
  } VP8DistoStats;
  
  // Compute the final SSIM value
  // The non-clipped version assumes stats->w = (2 * VP8_SSIM_KERNEL + 1)^2.
  double VP8SSIMFromStats(const VP8DistoStats* const stats);
  double VP8SSIMFromStatsClipped(const VP8DistoStats* const stats);
  
  #define VP8_SSIM_KERNEL 3   // total size of the kernel: 2 * VP8_SSIM_KERNEL + 1
  typedef double (*VP8SSIMGetClippedFunc)(const uint8_t* src1, int stride1,
                                          const uint8_t* src2, int stride2,
                                          int xo, int yo,  // center position
                                          int W, int H);   // plane dimension
  
  #if !defined(WEBP_REDUCE_SIZE)
  // This version is called with the guarantee that you can load 8 bytes and
  // 8 rows at offset src1 and src2
  typedef double (*VP8SSIMGetFunc)(const uint8_t* src1, int stride1,
                                   const uint8_t* src2, int stride2);
  
  extern VP8SSIMGetFunc VP8SSIMGet;         // unclipped / unchecked
  extern VP8SSIMGetClippedFunc VP8SSIMGetClipped;   // with clipping
  #endif
  
  #if !defined(WEBP_DISABLE_STATS)
  typedef uint32_t (*VP8AccumulateSSEFunc)(const uint8_t* src1,
                                           const uint8_t* src2, int len);
  extern VP8AccumulateSSEFunc VP8AccumulateSSE;
  #endif
  
  // must be called before using any of the above directly
  void VP8SSIMDspInit(void);
  
  //------------------------------------------------------------------------------
  // Decoding
  
  typedef void (*VP8DecIdct)(const int16_t* coeffs, uint8_t* dst);
  // when doing two transforms, coeffs is actually int16_t[2][16].
  typedef void (*VP8DecIdct2)(const int16_t* coeffs, uint8_t* dst, int do_two);
  extern VP8DecIdct2 VP8Transform;
  extern VP8DecIdct VP8TransformAC3;
  extern VP8DecIdct VP8TransformUV;
  extern VP8DecIdct VP8TransformDC;
  extern VP8DecIdct VP8TransformDCUV;
  extern VP8WHT VP8TransformWHT;
  
  // *dst is the destination block, with stride BPS. Boundary samples are
  // assumed accessible when needed.
  typedef void (*VP8PredFunc)(uint8_t* dst);
  extern VP8PredFunc VP8PredLuma16[/* NUM_B_DC_MODES */];
  extern VP8PredFunc VP8PredChroma8[/* NUM_B_DC_MODES */];
  extern VP8PredFunc VP8PredLuma4[/* NUM_BMODES */];
  
  // clipping tables (for filtering)
  extern const int8_t* const VP8ksclip1;  // clips [-1020, 1020] to [-128, 127]
  extern const int8_t* const VP8ksclip2;  // clips [-112, 112] to [-16, 15]
  extern const uint8_t* const VP8kclip1;  // clips [-255,511] to [0,255]
  extern const uint8_t* const VP8kabs0;   // abs(x) for x in [-255,255]
  // must be called first
  void VP8InitClipTables(void);
  
  // simple filter (only for luma)
  typedef void (*VP8SimpleFilterFunc)(uint8_t* p, int stride, int thresh);
  extern VP8SimpleFilterFunc VP8SimpleVFilter16;
  extern VP8SimpleFilterFunc VP8SimpleHFilter16;
  extern VP8SimpleFilterFunc VP8SimpleVFilter16i;  // filter 3 inner edges
  extern VP8SimpleFilterFunc VP8SimpleHFilter16i;
  
  // regular filter (on both macroblock edges and inner edges)
  typedef void (*VP8LumaFilterFunc)(uint8_t* luma, int stride,
                                    int thresh, int ithresh, int hev_t);
  typedef void (*VP8ChromaFilterFunc)(uint8_t* u, uint8_t* v, int stride,
                                      int thresh, int ithresh, int hev_t);
  // on outer edge
  extern VP8LumaFilterFunc VP8VFilter16;
  extern VP8LumaFilterFunc VP8HFilter16;
  extern VP8ChromaFilterFunc VP8VFilter8;
  extern VP8ChromaFilterFunc VP8HFilter8;
  
  // on inner edge
  extern VP8LumaFilterFunc VP8VFilter16i;   // filtering 3 inner edges altogether
  extern VP8LumaFilterFunc VP8HFilter16i;
  extern VP8ChromaFilterFunc VP8VFilter8i;  // filtering u and v altogether
  extern VP8ChromaFilterFunc VP8HFilter8i;
  
  // Dithering. Combines dithering values (centered around 128) with dst[],
  // according to: dst[] = clip(dst[] + (((dither[]-128) + 8) >> 4)
  #define VP8_DITHER_DESCALE 4
  #define VP8_DITHER_DESCALE_ROUNDER (1 << (VP8_DITHER_DESCALE - 1))
  #define VP8_DITHER_AMP_BITS 7
  #define VP8_DITHER_AMP_CENTER (1 << VP8_DITHER_AMP_BITS)
  extern void (*VP8DitherCombine8x8)(const uint8_t* dither, uint8_t* dst,
                                     int dst_stride);
  
  // must be called before anything using the above
  void VP8DspInit(void);
  
  //------------------------------------------------------------------------------
  // WebP I/O
  
  #define FANCY_UPSAMPLING   // undefined to remove fancy upsampling support
  
  // Convert a pair of y/u/v lines together to the output rgb/a colorspace.
  // bottom_y can be NULL if only one line of output is needed (at top/bottom).
  typedef void (*WebPUpsampleLinePairFunc)(
      const uint8_t* top_y, const uint8_t* bottom_y,
      const uint8_t* top_u, const uint8_t* top_v,
      const uint8_t* cur_u, const uint8_t* cur_v,
      uint8_t* top_dst, uint8_t* bottom_dst, int len);
  
  #ifdef FANCY_UPSAMPLING
  
  // Fancy upsampling functions to convert YUV to RGB(A) modes
  extern WebPUpsampleLinePairFunc WebPUpsamplers[/* MODE_LAST */];
  
  #endif    // FANCY_UPSAMPLING
  
  // Per-row point-sampling methods.
  typedef void (*WebPSamplerRowFunc)(const uint8_t* y,
                                     const uint8_t* u, const uint8_t* v,
                                     uint8_t* dst, int len);
  // Generic function to apply 'WebPSamplerRowFunc' to the whole plane:
  void WebPSamplerProcessPlane(const uint8_t* y, int y_stride,
                               const uint8_t* u, const uint8_t* v, int uv_stride,
                               uint8_t* dst, int dst_stride,
                               int width, int height, WebPSamplerRowFunc func);
  
  // Sampling functions to convert rows of YUV to RGB(A)
  extern WebPSamplerRowFunc WebPSamplers[/* MODE_LAST */];
  
  // General function for converting two lines of ARGB or RGBA.
  // 'alpha_is_last' should be true if 0xff000000 is stored in memory as
  // as 0x00, 0x00, 0x00, 0xff (little endian).
  WebPUpsampleLinePairFunc WebPGetLinePairConverter(int alpha_is_last);
  
  // YUV444->RGB converters
  typedef void (*WebPYUV444Converter)(const uint8_t* y,
                                      const uint8_t* u, const uint8_t* v,
                                      uint8_t* dst, int len);
  
  extern WebPYUV444Converter WebPYUV444Converters[/* MODE_LAST */];
  
  // Must be called before using the WebPUpsamplers[] (and for premultiplied
  // colorspaces like rgbA, rgbA4444, etc)
  void WebPInitUpsamplers(void);
  // Must be called before using WebPSamplers[]
  void WebPInitSamplers(void);
  // Must be called before using WebPYUV444Converters[]
  void WebPInitYUV444Converters(void);
  
  //------------------------------------------------------------------------------
  // ARGB -> YUV converters
  
  // Convert ARGB samples to luma Y.
  extern void (*WebPConvertARGBToY)(const uint32_t* argb, uint8_t* y, int width);
  // Convert ARGB samples to U/V with downsampling. do_store should be '1' for
  // even lines and '0' for odd ones. 'src_width' is the original width, not
  // the U/V one.
  extern void (*WebPConvertARGBToUV)(const uint32_t* argb, uint8_t* u, uint8_t* v,
                                     int src_width, int do_store);
  
  // Convert a row of accumulated (four-values) of rgba32 toward U/V
  extern void (*WebPConvertRGBA32ToUV)(const uint16_t* rgb,
                                       uint8_t* u, uint8_t* v, int width);
  
  // Convert RGB or BGR to Y
  extern void (*WebPConvertRGB24ToY)(const uint8_t* rgb, uint8_t* y, int width);
  extern void (*WebPConvertBGR24ToY)(const uint8_t* bgr, uint8_t* y, int width);
  
  // used for plain-C fallback.
  extern void WebPConvertARGBToUV_C(const uint32_t* argb, uint8_t* u, uint8_t* v,
                                    int src_width, int do_store);
  extern void WebPConvertRGBA32ToUV_C(const uint16_t* rgb,
                                      uint8_t* u, uint8_t* v, int width);
  
  // utilities for accurate RGB->YUV conversion
  extern uint64_t (*WebPSharpYUVUpdateY)(const uint16_t* src, const uint16_t* ref,
                                         uint16_t* dst, int len);
  extern void (*WebPSharpYUVUpdateRGB)(const int16_t* src, const int16_t* ref,
                                       int16_t* dst, int len);
  extern void (*WebPSharpYUVFilterRow)(const int16_t* A, const int16_t* B,
                                       int len,
                                       const uint16_t* best_y, uint16_t* out);
  
  // Must be called before using the above.
  void WebPInitConvertARGBToYUV(void);
  
  //------------------------------------------------------------------------------
  // Rescaler
  
  struct WebPRescaler;
  
  // Import a row of data and save its contribution in the rescaler.
  // 'channel' denotes the channel number to be imported. 'Expand' corresponds to
  // the wrk->x_expand case. Otherwise, 'Shrink' is to be used.
  typedef void (*WebPRescalerImportRowFunc)(struct WebPRescaler* const wrk,
                                            const uint8_t* src);
  
  extern WebPRescalerImportRowFunc WebPRescalerImportRowExpand;
  extern WebPRescalerImportRowFunc WebPRescalerImportRowShrink;
  
  // Export one row (starting at x_out position) from rescaler.
  // 'Expand' corresponds to the wrk->y_expand case.
  // Otherwise 'Shrink' is to be used
  typedef void (*WebPRescalerExportRowFunc)(struct WebPRescaler* const wrk);
  extern WebPRescalerExportRowFunc WebPRescalerExportRowExpand;
  extern WebPRescalerExportRowFunc WebPRescalerExportRowShrink;
  
  // Plain-C implementation, as fall-back.
  extern void WebPRescalerImportRowExpand_C(struct WebPRescaler* const wrk,
                                            const uint8_t* src);
  extern void WebPRescalerImportRowShrink_C(struct WebPRescaler* const wrk,
                                            const uint8_t* src);
  extern void WebPRescalerExportRowExpand_C(struct WebPRescaler* const wrk);
  extern void WebPRescalerExportRowShrink_C(struct WebPRescaler* const wrk);
  
  // Main entry calls:
  extern void WebPRescalerImportRow(struct WebPRescaler* const wrk,
                                    const uint8_t* src);
  // Export one row (starting at x_out position) from rescaler.
  extern void WebPRescalerExportRow(struct WebPRescaler* const wrk);
  
  // Must be called first before using the above.
  void WebPRescalerDspInit(void);
  
  //------------------------------------------------------------------------------
  // Utilities for processing transparent channel.
  
  // Apply alpha pre-multiply on an rgba, bgra or argb plane of size w * h.
  // alpha_first should be 0 for argb, 1 for rgba or bgra (where alpha is last).
  extern void (*WebPApplyAlphaMultiply)(
      uint8_t* rgba, int alpha_first, int w, int h, int stride);
  
  // Same, buf specifically for RGBA4444 format
  extern void (*WebPApplyAlphaMultiply4444)(
      uint8_t* rgba4444, int w, int h, int stride);
  
  // Dispatch the values from alpha[] plane to the ARGB destination 'dst'.
  // Returns true if alpha[] plane has non-trivial values different from 0xff.
  extern int (*WebPDispatchAlpha)(const uint8_t* alpha, int alpha_stride,
                                  int width, int height,
                                  uint8_t* dst, int dst_stride);
  
  // Transfer packed 8b alpha[] values to green channel in dst[], zero'ing the
  // A/R/B values. 'dst_stride' is the stride for dst[] in uint32_t units.
  extern void (*WebPDispatchAlphaToGreen)(const uint8_t* alpha, int alpha_stride,
                                          int width, int height,
                                          uint32_t* dst, int dst_stride);
  
  // Extract the alpha values from 32b values in argb[] and pack them into alpha[]
  // (this is the opposite of WebPDispatchAlpha).
  // Returns true if there's only trivial 0xff alpha values.
  extern int (*WebPExtractAlpha)(const uint8_t* argb, int argb_stride,
                                 int width, int height,
                                 uint8_t* alpha, int alpha_stride);
  
  // Extract the green values from 32b values in argb[] and pack them into alpha[]
  // (this is the opposite of WebPDispatchAlphaToGreen).
  extern void (*WebPExtractGreen)(const uint32_t* argb, uint8_t* alpha, int size);
  
  // Pre-Multiply operation transforms x into x * A / 255  (where x=Y,R,G or B).
  // Un-Multiply operation transforms x into x * 255 / A.
  
  // Pre-Multiply or Un-Multiply (if 'inverse' is true) argb values in a row.
  extern void (*WebPMultARGBRow)(uint32_t* const ptr, int width, int inverse);
  
  // Same a WebPMultARGBRow(), but for several rows.
  void WebPMultARGBRows(uint8_t* ptr, int stride, int width, int num_rows,
                        int inverse);
  
  // Same for a row of single values, with side alpha values.
  extern void (*WebPMultRow)(uint8_t* const ptr, const uint8_t* const alpha,
                             int width, int inverse);
  
  // Same a WebPMultRow(), but for several 'num_rows' rows.
  void WebPMultRows(uint8_t* ptr, int stride,
                    const uint8_t* alpha, int alpha_stride,
                    int width, int num_rows, int inverse);
  
  // Plain-C versions, used as fallback by some implementations.
  void WebPMultRow_C(uint8_t* const ptr, const uint8_t* const alpha,
                     int width, int inverse);
  void WebPMultARGBRow_C(uint32_t* const ptr, int width, int inverse);
  
  #ifdef WORDS_BIGENDIAN
  // ARGB packing function: a/r/g/b input is rgba or bgra order.
  extern void (*WebPPackARGB)(const uint8_t* a, const uint8_t* r,
                              const uint8_t* g, const uint8_t* b, int len,
                              uint32_t* out);
  #endif
  
  // RGB packing function. 'step' can be 3 or 4. r/g/b input is rgb or bgr order.
  extern void (*WebPPackRGB)(const uint8_t* r, const uint8_t* g, const uint8_t* b,
                             int len, int step, uint32_t* out);
  
  // This function returns true if src[i] contains a value different from 0xff.
  extern int (*WebPHasAlpha8b)(const uint8_t* src, int length);
  // This function returns true if src[4*i] contains a value different from 0xff.
  extern int (*WebPHasAlpha32b)(const uint8_t* src, int length);
  // replaces transparent values in src[] by 'color'.
  extern void (*WebPAlphaReplace)(uint32_t* src, int length, uint32_t color);
  
  // To be called first before using the above.
  void WebPInitAlphaProcessing(void);
  
  //------------------------------------------------------------------------------
  // Filter functions
  
  typedef enum {     // Filter types.
    WEBP_FILTER_NONE = 0,
    WEBP_FILTER_HORIZONTAL,
    WEBP_FILTER_VERTICAL,
    WEBP_FILTER_GRADIENT,
    WEBP_FILTER_LAST = WEBP_FILTER_GRADIENT + 1,  // end marker
    WEBP_FILTER_BEST,    // meta-types
    WEBP_FILTER_FAST
  } WEBP_FILTER_TYPE;
  
  typedef void (*WebPFilterFunc)(const uint8_t* in, int width, int height,
                                 int stride, uint8_t* out);
  // In-place un-filtering.
  // Warning! 'prev_line' pointer can be equal to 'cur_line' or 'preds'.
  typedef void (*WebPUnfilterFunc)(const uint8_t* prev_line, const uint8_t* preds,
                                   uint8_t* cur_line, int width);
  
  // Filter the given data using the given predictor.
  // 'in' corresponds to a 2-dimensional pixel array of size (stride * height)
  // in raster order.
  // 'stride' is number of bytes per scan line (with possible padding).
  // 'out' should be pre-allocated.
  extern WebPFilterFunc WebPFilters[WEBP_FILTER_LAST];
  
  // In-place reconstruct the original data from the given filtered data.
  // The reconstruction will be done for 'num_rows' rows starting from 'row'
  // (assuming rows upto 'row - 1' are already reconstructed).
  extern WebPUnfilterFunc WebPUnfilters[WEBP_FILTER_LAST];
  
  // To be called first before using the above.
  void VP8FiltersInit(void);
  
  #ifdef __cplusplus
  }    // extern "C"
  #endif
  
  #endif  // WEBP_DSP_DSP_H_
  