// Copyright 2017 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.

// -----------------------------------------------------------------------------

//

// distortion calculation

//

// Author: Skal (pascal.massimino@gmail.com)

#include <assert.h>

#include <stdlib.h>  // for abs()

#include "src/dsp/dsp.h"

#if !defined(WEBP_REDUCE_SIZE)

//------------------------------------------------------------------------------

// SSIM / PSNR

// hat-shaped filter. Sum of coefficients is equal to 16.

static const uint32_t kWeight[2 * VP8_SSIM_KERNEL + 1] = {

  1, 2, 3, 4, 3, 2, 1

};

static const uint32_t kWeightSum = 16 * 16;   // sum{kWeight}^2

static WEBP_INLINE double SSIMCalculation(

    const VP8DistoStats* const stats, uint32_t N  /*num samples*/) {

  const uint32_t w2 =  N * N;

  const uint32_t C1 = 20 * w2;

  const uint32_t C2 = 60 * w2;

  const uint32_t C3 = 8 * 8 * w2;   // 'dark' limit ~= 6

  const uint64_t xmxm = (uint64_t)stats->xm * stats->xm;

  const uint64_t ymym = (uint64_t)stats->ym * stats->ym;

  if (xmxm + ymym >= C3) {

    const int64_t xmym = (int64_t)stats->xm * stats->ym;

    const int64_t sxy = (int64_t)stats->xym * N - xmym;    // can be negative

    const uint64_t sxx = (uint64_t)stats->xxm * N - xmxm;

    const uint64_t syy = (uint64_t)stats->yym * N - ymym;

    // we descale by 8 to prevent overflow during the fnum/fden multiply.

    const uint64_t num_S = (2 * (uint64_t)(sxy < 0 ? 0 : sxy) + C2) >> 8;

    const uint64_t den_S = (sxx + syy + C2) >> 8;

    const uint64_t fnum = (2 * xmym + C1) * num_S;

    const uint64_t fden = (xmxm + ymym + C1) * den_S;

    const double r = (double)fnum / fden;

    assert(r >= 0. && r <= 1.0);

    return r;

  }

  return 1.;   // area is too dark to contribute meaningfully

}

double VP8SSIMFromStats(const VP8DistoStats* const stats) {

  return SSIMCalculation(stats, kWeightSum);

}

double VP8SSIMFromStatsClipped(const VP8DistoStats* const stats) {

  return SSIMCalculation(stats, stats->w);

}

static double SSIMGetClipped_C(const uint8_t* src1, int stride1,

                               const uint8_t* src2, int stride2,

                               int xo, int yo, int W, int H) {

  VP8DistoStats stats = { 0, 0, 0, 0, 0, 0 };

  const int ymin = (yo - VP8_SSIM_KERNEL < 0) ? 0 : yo - VP8_SSIM_KERNEL;

  const int ymax = (yo + VP8_SSIM_KERNEL > H - 1) ? H - 1

                                                  : yo + VP8_SSIM_KERNEL;

  const int xmin = (xo - VP8_SSIM_KERNEL < 0) ? 0 : xo - VP8_SSIM_KERNEL;

  const int xmax = (xo + VP8_SSIM_KERNEL > W - 1) ? W - 1

                                                  : xo + VP8_SSIM_KERNEL;

  int x, y;

  src1 += ymin * stride1;

  src2 += ymin * stride2;

  for (y = ymin; y <= ymax; ++y, src1 += stride1, src2 += stride2) {

    for (x = xmin; x <= xmax; ++x) {

      const uint32_t w = kWeight[VP8_SSIM_KERNEL + x - xo]

                       * kWeight[VP8_SSIM_KERNEL + y - yo];

      const uint32_t s1 = src1[x];

      const uint32_t s2 = src2[x];

      stats.w   += w;

      stats.xm  += w * s1;

      stats.ym  += w * s2;

      stats.xxm += w * s1 * s1;

      stats.xym += w * s1 * s2;

      stats.yym += w * s2 * s2;

    }

  }

  return VP8SSIMFromStatsClipped(&stats);

}

static double SSIMGet_C(const uint8_t* src1, int stride1,

                        const uint8_t* src2, int stride2) {

  VP8DistoStats stats = { 0, 0, 0, 0, 0, 0 };

  int x, y;

  for (y = 0; y <= 2 * VP8_SSIM_KERNEL; ++y, src1 += stride1, src2 += stride2) {

    for (x = 0; x <= 2 * VP8_SSIM_KERNEL; ++x) {

      const uint32_t w = kWeight[x] * kWeight[y];

      const uint32_t s1 = src1[x];

      const uint32_t s2 = src2[x];

      stats.xm  += w * s1;

      stats.ym  += w * s2;

      stats.xxm += w * s1 * s1;

      stats.xym += w * s1 * s2;

      stats.yym += w * s2 * s2;

    }

  }

  return VP8SSIMFromStats(&stats);

}

#endif  // !defined(WEBP_REDUCE_SIZE)

//------------------------------------------------------------------------------

#if !defined(WEBP_DISABLE_STATS)

static uint32_t AccumulateSSE_C(const uint8_t* src1,

                                const uint8_t* src2, int len) {

  int i;

  uint32_t sse2 = 0;

  assert(len <= 65535);  // to ensure that accumulation fits within uint32_t

  for (i = 0; i < len; ++i) {

    const int32_t diff = src1[i] - src2[i];

    sse2 += diff * diff;

  }

  return sse2;

}

#endif

//------------------------------------------------------------------------------

#if !defined(WEBP_REDUCE_SIZE)

VP8SSIMGetFunc VP8SSIMGet;

VP8SSIMGetClippedFunc VP8SSIMGetClipped;

#endif

#if !defined(WEBP_DISABLE_STATS)

VP8AccumulateSSEFunc VP8AccumulateSSE;

#endif

extern void VP8SSIMDspInitSSE2(void);

WEBP_DSP_INIT_FUNC(VP8SSIMDspInit) {

#if !defined(WEBP_REDUCE_SIZE)

  VP8SSIMGetClipped = SSIMGetClipped_C;

  VP8SSIMGet = SSIMGet_C;

#endif

#if !defined(WEBP_DISABLE_STATS)

  VP8AccumulateSSE = AccumulateSSE_C;

#endif

  if (VP8GetCPUInfo != NULL) {

#if defined(WEBP_USE_SSE2)

    if (VP8GetCPUInfo(kSSE2)) {

      VP8SSIMDspInitSSE2();

    }

#endif

  }

}