// Copyright 2010 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.

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

//

// Frame-reconstruction function. Memory allocation.

//

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

#include <assert.h>

#include <stdlib.h>

#include <string.h>

#include "src/dec/common_dec.h"

#include "src/dec/vp8_dec.h"

#include "src/dec/vp8i_dec.h"

#include "src/dec/webpi_dec.h"

#include "src/dsp/dsp.h"

#include "src/utils/random_utils.h"

#include "src/utils/thread_utils.h"

#include "src/utils/utils.h"

#include "src/webp/decode.h"

#include "src/webp/types.h"

WEBP_ASSUME_UNSAFE_INDEXABLE_ABI

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

// Main reconstruction function.

static const uint16_t kScan[16] = {

    0 + 0 * BPS,  4 + 0 * BPS,  8 + 0 * BPS,  12 + 0 * BPS,

    0 + 4 * BPS,  4 + 4 * BPS,  8 + 4 * BPS,  12 + 4 * BPS,

    0 + 8 * BPS,  4 + 8 * BPS,  8 + 8 * BPS,  12 + 8 * BPS,

    0 + 12 * BPS, 4 + 12 * BPS, 8 + 12 * BPS, 12 + 12 * BPS};

static int CheckMode(int mb_x, int mb_y, int mode) {

  if (mode == B_DC_PRED) {

    if (mb_x == 0) {

      return (mb_y == 0) ? B_DC_PRED_NOTOPLEFT : B_DC_PRED_NOLEFT;

    } else {

      return (mb_y == 0) ? B_DC_PRED_NOTOP : B_DC_PRED;

    }

  }

  return mode;

}

static void Copy32b(uint8_t* const dst, const uint8_t* const src) {

  WEBP_UNSAFE_MEMCPY(dst, src, 4);

}

static WEBP_INLINE void DoTransform(uint32_t bits, const int16_t* const src,

                                    uint8_t* const dst) {

  switch (bits >> 30) {

    case 3:

      VP8Transform(src, dst, 0);

      break;

    case 2:

      VP8TransformAC3(src, dst);

      break;

    case 1:

      VP8TransformDC(src, dst);

      break;

    default:

      break;

  }

}

static void DoUVTransform(uint32_t bits, const int16_t* const src,

                          uint8_t* const dst) {

  if (bits & 0xff) {             // any non-zero coeff at all?

    if (bits & 0xaa) {           // any non-zero AC coefficient?

      VP8TransformUV(src, dst);  // note we don't use the AC3 variant for U/V

    } else {

      VP8TransformDCUV(src, dst);

    }

  }

}

static void ReconstructRow(const VP8Decoder* const dec,

                           const VP8ThreadContext* ctx) {

  int j;

  int mb_x;

  const int mb_y = ctx->mb_y;

  const int cache_id = ctx->id;

  uint8_t* const y_dst = dec->yuv_b + Y_OFF;

  uint8_t* const u_dst = dec->yuv_b + U_OFF;

  uint8_t* const v_dst = dec->yuv_b + V_OFF;

  // Initialize left-most block.

  for (j = 0; j < 16; ++j) {

    y_dst[j * BPS - 1] = 129;

  }

  for (j = 0; j < 8; ++j) {

    u_dst[j * BPS - 1] = 129;

    v_dst[j * BPS - 1] = 129;

  }

  // Init top-left sample on left column too.

  if (mb_y > 0) {

    y_dst[-1 - BPS] = u_dst[-1 - BPS] = v_dst[-1 - BPS] = 129;

  } else {

    // we only need to do this init once at block (0,0).

    // Afterward, it remains valid for the whole topmost row.

    WEBP_UNSAFE_MEMSET(y_dst - BPS - 1, 127, 16 + 4 + 1);

    WEBP_UNSAFE_MEMSET(u_dst - BPS - 1, 127, 8 + 1);

    WEBP_UNSAFE_MEMSET(v_dst - BPS - 1, 127, 8 + 1);

  }

  // Reconstruct one row.

  for (mb_x = 0; mb_x < dec->mb_w; ++mb_x) {

    const VP8MBData* const block = ctx->mb_data + mb_x;

    // Rotate in the left samples from previously decoded block. We move four

    // pixels at a time for alignment reason, and because of in-loop filter.

    if (mb_x > 0) {

      for (j = -1; j < 16; ++j) {

        Copy32b(&y_dst[j * BPS - 4], &y_dst[j * BPS + 12]);

      }

      for (j = -1; j < 8; ++j) {

        Copy32b(&u_dst[j * BPS - 4], &u_dst[j * BPS + 4]);

        Copy32b(&v_dst[j * BPS - 4], &v_dst[j * BPS + 4]);

      }

    }

    {

      // bring top samples into the cache

      VP8TopSamples* const top_yuv = dec->yuv_t + mb_x;

      const int16_t* const coeffs = block->coeffs;

      uint32_t bits = block->non_zero_y;

      int n;

      if (mb_y > 0) {

        WEBP_UNSAFE_MEMCPY(y_dst - BPS, top_yuv[0].y, 16);

        WEBP_UNSAFE_MEMCPY(u_dst - BPS, top_yuv[0].u, 8);

        WEBP_UNSAFE_MEMCPY(v_dst - BPS, top_yuv[0].v, 8);

      }

      // predict and add residuals

      if (block->is_i4x4) {  // 4x4

        uint32_t* const top_right = (uint32_t*)(y_dst - BPS + 16);

        if (mb_y > 0) {

          if (mb_x >= dec->mb_w - 1) {  // on rightmost border

            WEBP_UNSAFE_MEMSET(top_right, top_yuv[0].y[15], sizeof(*top_right));

          } else {

            WEBP_UNSAFE_MEMCPY(top_right, top_yuv[1].y, sizeof(*top_right));

          }

        }

        // replicate the top-right pixels below

        top_right[BPS] = top_right[2 * BPS] = top_right[3 * BPS] = top_right[0];

        // predict and add residuals for all 4x4 blocks in turn.

        for (n = 0; n < 16; ++n, bits <<= 2) {

          uint8_t* const dst = y_dst + kScan[n];

          VP8PredLuma4[block->imodes[n]](dst);

          DoTransform(bits, coeffs + n * 16, dst);

        }

      } else {  // 16x16

        const int pred_func = CheckMode(mb_x, mb_y, block->imodes[0]);

        VP8PredLuma16[pred_func](y_dst);

        if (bits != 0) {

          for (n = 0; n < 16; ++n, bits <<= 2) {

            DoTransform(bits, coeffs + n * 16, y_dst + kScan[n]);

          }

        }

      }

      {

        // Chroma

        const uint32_t bits_uv = block->non_zero_uv;

        const int pred_func = CheckMode(mb_x, mb_y, block->uvmode);

        VP8PredChroma8[pred_func](u_dst);

        VP8PredChroma8[pred_func](v_dst);

        DoUVTransform(bits_uv >> 0, coeffs + 16 * 16, u_dst);

        DoUVTransform(bits_uv >> 8, coeffs + 20 * 16, v_dst);

      }

      // stash away top samples for next block

      if (mb_y < dec->mb_h - 1) {

        WEBP_UNSAFE_MEMCPY(top_yuv[0].y, y_dst + 15 * BPS, 16);

        WEBP_UNSAFE_MEMCPY(top_yuv[0].u, u_dst + 7 * BPS, 8);

        WEBP_UNSAFE_MEMCPY(top_yuv[0].v, v_dst + 7 * BPS, 8);

      }

    }

    // Transfer reconstructed samples from yuv_b cache to final destination.

    {

      const int y_offset = cache_id * 16 * dec->cache_y_stride;

      const int uv_offset = cache_id * 8 * dec->cache_uv_stride;

      uint8_t* const y_out = dec->cache_y + mb_x * 16 + y_offset;

      uint8_t* const u_out = dec->cache_u + mb_x * 8 + uv_offset;

      uint8_t* const v_out = dec->cache_v + mb_x * 8 + uv_offset;

      for (j = 0; j < 16; ++j) {

        WEBP_UNSAFE_MEMCPY(y_out + j * dec->cache_y_stride, y_dst + j * BPS,

                           16);

      }

      for (j = 0; j < 8; ++j) {

        WEBP_UNSAFE_MEMCPY(u_out + j * dec->cache_uv_stride, u_dst + j * BPS,

                           8);

        WEBP_UNSAFE_MEMCPY(v_out + j * dec->cache_uv_stride, v_dst + j * BPS,

                           8);

      }

    }

  }

}

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

// Filtering

// kFilterExtraRows[] = How many extra lines are needed on the MB boundary

// for caching, given a filtering level.

// Simple filter:  up to 2 luma samples are read and 1 is written.

// Complex filter: up to 4 luma samples are read and 3 are written. Same for

//                 U/V, so it's 8 samples total (because of the 2x upsampling).

static const uint8_t kFilterExtraRows[3] = {0, 2, 8};

static void DoFilter(const VP8Decoder* const dec, int mb_x, int mb_y) {

  const VP8ThreadContext* const ctx = &dec->thread_ctx;

  const int cache_id = ctx->id;

  const int y_bps = dec->cache_y_stride;

  const VP8FInfo* const f_info = ctx->f_info + mb_x;

  uint8_t* const y_dst = dec->cache_y + cache_id * 16 * y_bps + mb_x * 16;

  const int ilevel = f_info->f_ilevel;

  const int limit = f_info->f_limit;

  if (limit == 0) {

    return;

  }

  assert(limit >= 3);

  if (dec->filter_type == 1) {  // simple

    if (mb_x > 0) {

      VP8SimpleHFilter16(y_dst, y_bps, limit + 4);

    }

    if (f_info->f_inner) {

      VP8SimpleHFilter16i(y_dst, y_bps, limit);

    }

    if (mb_y > 0) {

      VP8SimpleVFilter16(y_dst, y_bps, limit + 4);

    }

    if (f_info->f_inner) {

      VP8SimpleVFilter16i(y_dst, y_bps, limit);

    }

  } else {  // complex

    const int uv_bps = dec->cache_uv_stride;

    uint8_t* const u_dst = dec->cache_u + cache_id * 8 * uv_bps + mb_x * 8;

    uint8_t* const v_dst = dec->cache_v + cache_id * 8 * uv_bps + mb_x * 8;

    const int hev_thresh = f_info->hev_thresh;

    if (mb_x > 0) {

      VP8HFilter16(y_dst, y_bps, limit + 4, ilevel, hev_thresh);

      VP8HFilter8(u_dst, v_dst, uv_bps, limit + 4, ilevel, hev_thresh);

    }

    if (f_info->f_inner) {

      VP8HFilter16i(y_dst, y_bps, limit, ilevel, hev_thresh);

      VP8HFilter8i(u_dst, v_dst, uv_bps, limit, ilevel, hev_thresh);

    }

    if (mb_y > 0) {

      VP8VFilter16(y_dst, y_bps, limit + 4, ilevel, hev_thresh);

      VP8VFilter8(u_dst, v_dst, uv_bps, limit + 4, ilevel, hev_thresh);

    }

    if (f_info->f_inner) {

      VP8VFilter16i(y_dst, y_bps, limit, ilevel, hev_thresh);

      VP8VFilter8i(u_dst, v_dst, uv_bps, limit, ilevel, hev_thresh);

    }

  }

}

// Filter the decoded macroblock row (if needed)

static void FilterRow(const VP8Decoder* const dec) {

  int mb_x;

  const int mb_y = dec->thread_ctx.mb_y;

  assert(dec->thread_ctx.filter_row);

  for (mb_x = dec->tl_mb_x; mb_x < dec->br_mb_x; ++mb_x) {

    DoFilter(dec, mb_x, mb_y);

  }

}

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

// Precompute the filtering strength for each segment and each i4x4/i16x16 mode.

static void PrecomputeFilterStrengths(VP8Decoder* const dec) {

  if (dec->filter_type > 0) {

    int s;

    const VP8FilterHeader* const hdr = &dec->filter_hdr;

    for (s = 0; s < NUM_MB_SEGMENTS; ++s) {

      int i4x4;

      // First, compute the initial level

      int base_level;

      if (dec->segment_hdr.use_segment) {

        base_level = dec->segment_hdr.filter_strength[s];

        if (!dec->segment_hdr.absolute_delta) {

          base_level += hdr->level;

        }

      } else {

        base_level = hdr->level;

      }

      for (i4x4 = 0; i4x4 <= 1; ++i4x4) {

        VP8FInfo* const info = &dec->fstrengths[s][i4x4];

        int level = base_level;

        if (hdr->use_lf_delta) {

          level += hdr->ref_lf_delta[0];

          if (i4x4) {

            level += hdr->mode_lf_delta[0];

          }

        }

        level = (level < 0) ? 0 : (level > 63) ? 63 : level;

        if (level > 0) {

          int ilevel = level;

          if (hdr->sharpness > 0) {

            if (hdr->sharpness > 4) {

              ilevel >>= 2;

            } else {

              ilevel >>= 1;

            }

            if (ilevel > 9 - hdr->sharpness) {

              ilevel = 9 - hdr->sharpness;

            }

          }

          if (ilevel < 1) ilevel = 1;

          info->f_ilevel = ilevel;

          info->f_limit = 2 * level + ilevel;

          info->hev_thresh = (level >= 40) ? 2 : (level >= 15) ? 1 : 0;

        } else {

          info->f_limit = 0;  // no filtering

        }

        info->f_inner = i4x4;

      }

    }

  }

}

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

// Dithering

// minimal amp that will provide a non-zero dithering effect

#define MIN_DITHER_AMP 4

#define DITHER_AMP_TAB_SIZE 12

static const uint8_t kQuantToDitherAmp[DITHER_AMP_TAB_SIZE] = {

    // roughly, it's dqm->uv_mat[1]

    8, 7, 6, 4, 4, 2, 2, 2, 1, 1, 1, 1};

void VP8InitDithering(const WebPDecoderOptions* const options,

                      VP8Decoder* const dec) {

  assert(dec != NULL);

  if (options != NULL) {

    const int d = options->dithering_strength;

    const int max_amp = (1 << VP8_RANDOM_DITHER_FIX) - 1;

    const int f = (d < 0) ? 0 : (d > 100) ? max_amp : (d * max_amp / 100);

    if (f > 0) {

      int s;

      int all_amp = 0;

      for (s = 0; s < NUM_MB_SEGMENTS; ++s) {

        VP8QuantMatrix* const dqm = &dec->dqm[s];

        if (dqm->uv_quant < DITHER_AMP_TAB_SIZE) {

          const int idx = (dqm->uv_quant < 0) ? 0 : dqm->uv_quant;

          dqm->dither = (f * kQuantToDitherAmp[idx]) >> 3;

        }

        all_amp |= dqm->dither;

      }

      if (all_amp != 0) {

        VP8InitRandom(&dec->dithering_rg, 1.0f);

        dec->dither = 1;

      }

    }

    // potentially allow alpha dithering

    dec->alpha_dithering = options->alpha_dithering_strength;

    if (dec->alpha_dithering > 100) {

      dec->alpha_dithering = 100;

    } else if (dec->alpha_dithering < 0) {

      dec->alpha_dithering = 0;

    }

  }

}

// Convert to range: [-2,2] for dither=50, [-4,4] for dither=100

static void Dither8x8(VP8Random* const rg, uint8_t* dst, int bps, int amp) {

  uint8_t dither[64];

  int i;

  for (i = 0; i < 8 * 8; ++i) {

    dither[i] = VP8RandomBits2(rg, VP8_DITHER_AMP_BITS + 1, amp);

  }

  VP8DitherCombine8x8(dither, dst, bps);

}

static void DitherRow(VP8Decoder* const dec) {

  int mb_x;

  assert(dec->dither);

  for (mb_x = dec->tl_mb_x; mb_x < dec->br_mb_x; ++mb_x) {

    const VP8ThreadContext* const ctx = &dec->thread_ctx;

    const VP8MBData* const data = ctx->mb_data + mb_x;

    const int cache_id = ctx->id;

    const int uv_bps = dec->cache_uv_stride;

    if (data->dither >= MIN_DITHER_AMP) {

      uint8_t* const u_dst = dec->cache_u + cache_id * 8 * uv_bps + mb_x * 8;

      uint8_t* const v_dst = dec->cache_v + cache_id * 8 * uv_bps + mb_x * 8;

      Dither8x8(&dec->dithering_rg, u_dst, uv_bps, data->dither);

      Dither8x8(&dec->dithering_rg, v_dst, uv_bps, data->dither);

    }

  }

}

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

// This function is called after a row of macroblocks is finished decoding.

// It also takes into account the following restrictions:

//  * In case of in-loop filtering, we must hold off sending some of the bottom

//    pixels as they are yet unfiltered. They will be when the next macroblock

//    row is decoded. Meanwhile, we must preserve them by rotating them in the

//    cache area. This doesn't hold for the very bottom row of the uncropped

//    picture of course.

//  * we must clip the remaining pixels against the cropping area. The VP8Io

//    struct must have the following fields set correctly before calling put():

#define MACROBLOCK_VPOS(mb_y) ((mb_y) * 16)  // vertical position of a MB

// Finalize and transmit a complete row. Return false in case of user-abort.

static int FinishRow(void* arg1, void* arg2) {

  VP8Decoder* const dec = (VP8Decoder*)arg1;

  VP8Io* const io = (VP8Io*)arg2;

  int ok = 1;

  const VP8ThreadContext* const ctx = &dec->thread_ctx;

  const int cache_id = ctx->id;

  const int extra_y_rows = kFilterExtraRows[dec->filter_type];

  const int ysize = extra_y_rows * dec->cache_y_stride;

  const int uvsize = (extra_y_rows / 2) * dec->cache_uv_stride;

  const int y_offset = cache_id * 16 * dec->cache_y_stride;

  const int uv_offset = cache_id * 8 * dec->cache_uv_stride;

  uint8_t* const ydst = dec->cache_y - ysize + y_offset;

  uint8_t* const udst = dec->cache_u - uvsize + uv_offset;

  uint8_t* const vdst = dec->cache_v - uvsize + uv_offset;

  const int mb_y = ctx->mb_y;

  const int is_first_row = (mb_y == 0);

  const int is_last_row = (mb_y >= dec->br_mb_y - 1);

  if (dec->mt_method == 2) {

    ReconstructRow(dec, ctx);

  }

  if (ctx->filter_row) {

    FilterRow(dec);

  }

  if (dec->dither) {

    DitherRow(dec);

  }

  if (io->put != NULL) {

    int y_start = MACROBLOCK_VPOS(mb_y);

    int y_end = MACROBLOCK_VPOS(mb_y + 1);

    if (!is_first_row) {

      y_start -= extra_y_rows;

      io->y = ydst;

      io->u = udst;

      io->v = vdst;

    } else {

      io->y = dec->cache_y + y_offset;

      io->u = dec->cache_u + uv_offset;

      io->v = dec->cache_v + uv_offset;

    }

    if (!is_last_row) {

      y_end -= extra_y_rows;

    }

    if (y_end > io->crop_bottom) {

      y_end = io->crop_bottom;  // make sure we don't overflow on last row.

    }

    // If dec->alpha_data is not NULL, we have some alpha plane present.

    io->a = NULL;

    if (dec->alpha_data != NULL && y_start < y_end) {

      io->a = VP8DecompressAlphaRows(dec, io, y_start, y_end - y_start);

      if (io->a == NULL) {

        return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,

                           "Could not decode alpha data.");

      }

    }

    if (y_start < io->crop_top) {

      const int delta_y = io->crop_top - y_start;

      y_start = io->crop_top;

      assert(!(delta_y & 1));

      io->y += dec->cache_y_stride * delta_y;

      io->u += dec->cache_uv_stride * (delta_y >> 1);

      io->v += dec->cache_uv_stride * (delta_y >> 1);

      if (io->a != NULL) {

        io->a += io->width * delta_y;

      }

    }

    if (y_start < y_end) {

      io->y += io->crop_left;

      io->u += io->crop_left >> 1;

      io->v += io->crop_left >> 1;

      if (io->a != NULL) {

        io->a += io->crop_left;

      }

      io->mb_y = y_start - io->crop_top;

      io->mb_w = io->crop_right - io->crop_left;

      io->mb_h = y_end - y_start;

      ok = io->put(io);

    }

  }

  // rotate top samples if needed

  if (cache_id + 1 == dec->num_caches) {

    if (!is_last_row) {

      WEBP_UNSAFE_MEMCPY(dec->cache_y - ysize, ydst + 16 * dec->cache_y_stride,

                         ysize);

      WEBP_UNSAFE_MEMCPY(dec->cache_u - uvsize, udst + 8 * dec->cache_uv_stride,

                         uvsize);

      WEBP_UNSAFE_MEMCPY(dec->cache_v - uvsize, vdst + 8 * dec->cache_uv_stride,

                         uvsize);

    }

  }

  return ok;

}

#undef MACROBLOCK_VPOS

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

int VP8ProcessRow(VP8Decoder* const dec, VP8Io* const io) {

  int ok = 1;

  VP8ThreadContext* const ctx = &dec->thread_ctx;

  const int filter_row = (dec->filter_type > 0) &&

                         (dec->mb_y >= dec->tl_mb_y) &&

                         (dec->mb_y <= dec->br_mb_y);

  if (dec->mt_method == 0) {

    // ctx->id and ctx->f_info are already set

    ctx->mb_y = dec->mb_y;

    ctx->filter_row = filter_row;

    ReconstructRow(dec, ctx);

    ok = FinishRow(dec, io);

  } else {

    WebPWorker* const worker = &dec->worker;

    // Finish previous job *before* updating context

    ok &= WebPGetWorkerInterface()->Sync(worker);

    assert(worker->status == OK);

    if (ok) {  // spawn a new deblocking/output job

      ctx->io = *io;

      ctx->id = dec->cache_id;

      ctx->mb_y = dec->mb_y;

      ctx->filter_row = filter_row;

      if (dec->mt_method == 2) {  // swap macroblock data

        VP8MBData* const tmp = ctx->mb_data;

        ctx->mb_data = dec->mb_data;

        dec->mb_data = tmp;

      } else {

        // perform reconstruction directly in main thread

        ReconstructRow(dec, ctx);

      }

      if (filter_row) {  // swap filter info

        VP8FInfo* const tmp = ctx->f_info;

        ctx->f_info = dec->f_info;

        dec->f_info = tmp;

      }

      // (reconstruct)+filter in parallel

      WebPGetWorkerInterface()->Launch(worker);

      if (++dec->cache_id == dec->num_caches) {

        dec->cache_id = 0;

      }

    }

  }

  return ok;

}

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

// Finish setting up the decoding parameter once user's setup() is called.

VP8StatusCode VP8EnterCritical(VP8Decoder* const dec, VP8Io* const io) {

  // Call setup() first. This may trigger additional decoding features on 'io'.

  // Note: Afterward, we must call teardown() no matter what.

  if (io->setup != NULL && !io->setup(io)) {

    VP8SetError(dec, VP8_STATUS_INVALID_PARAM, "Frame setup failed");

    return dec->status;

  }

  // Disable filtering per user request

  if (io->bypass_filtering) {

    dec->filter_type = 0;

  }

  // Define the area where we can skip in-loop filtering, in case of cropping.

  //

  // 'Simple' filter reads two luma samples outside of the macroblock

  // and filters one. It doesn't filter the chroma samples. Hence, we can

  // avoid doing the in-loop filtering before crop_top/crop_left position.

  // For the 'Complex' filter, 3 samples are read and up to 3 are filtered.

  // Means: there's a dependency chain that goes all the way up to the

  // top-left corner of the picture (MB #0). We must filter all the previous

  // macroblocks.

  {

    const int extra_pixels = kFilterExtraRows[dec->filter_type];

    if (dec->filter_type == 2) {

      // For complex filter, we need to preserve the dependency chain.

      dec->tl_mb_x = 0;

      dec->tl_mb_y = 0;

    } else {

      // For simple filter, we can filter only the cropped region.

      // We include 'extra_pixels' on the other side of the boundary, since

      // vertical or horizontal filtering of the previous macroblock can

      // modify some abutting pixels.

      dec->tl_mb_x = (io->crop_left - extra_pixels) >> 4;

      dec->tl_mb_y = (io->crop_top - extra_pixels) >> 4;

      if (dec->tl_mb_x < 0) dec->tl_mb_x = 0;

      if (dec->tl_mb_y < 0) dec->tl_mb_y = 0;

    }

    // We need some 'extra' pixels on the right/bottom.

    dec->br_mb_y = (io->crop_bottom + 15 + extra_pixels) >> 4;

    dec->br_mb_x = (io->crop_right + 15 + extra_pixels) >> 4;

    if (dec->br_mb_x > dec->mb_w) {

      dec->br_mb_x = dec->mb_w;

    }

    if (dec->br_mb_y > dec->mb_h) {

      dec->br_mb_y = dec->mb_h;

    }

  }

  PrecomputeFilterStrengths(dec);

  return VP8_STATUS_OK;

}

int VP8ExitCritical(VP8Decoder* const dec, VP8Io* const io) {

  int ok = 1;

  if (dec->mt_method > 0) {

    ok = WebPGetWorkerInterface()->Sync(&dec->worker);

  }

  if (io->teardown != NULL) {

    io->teardown(io);

  }

  return ok;

}

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

// For multi-threaded decoding we need to use 3 rows of 16 pixels as delay line.

//

// Reason is: the deblocking filter cannot deblock the bottom horizontal edges

// immediately, and needs to wait for first few rows of the next macroblock to

// be decoded. Hence, deblocking is lagging behind by 4 or 8 pixels (depending

// on strength).

// With two threads, the vertical positions of the rows being decoded are:

// Decode:  [ 0..15][16..31][32..47][48..63][64..79][...

// Deblock:         [ 0..11][12..27][28..43][44..59][...

// If we use two threads and two caches of 16 pixels, the sequence would be:

// Decode:  [ 0..15][16..31][ 0..15!!][16..31][ 0..15][...

// Deblock:         [ 0..11][12..27!!][-4..11][12..27][...

// The problem occurs during row [12..15!!] that both the decoding and

// deblocking threads are writing simultaneously.

// With 3 cache lines, one get a safe write pattern:

// Decode:  [ 0..15][16..31][32..47][ 0..15][16..31][32..47][0..

// Deblock:         [ 0..11][12..27][28..43][-4..11][12..27][28...

// Note that multi-threaded output _without_ deblocking can make use of two

// cache lines of 16 pixels only, since there's no lagging behind. The decoding

// and output process have non-concurrent writing:

// Decode:  [ 0..15][16..31][ 0..15][16..31][...

// io->put:         [ 0..15][16..31][ 0..15][...

#define MT_CACHE_LINES 3

#define ST_CACHE_LINES 1  // 1 cache row only for single-threaded case

// Initialize multi/single-thread worker

static int InitThreadContext(VP8Decoder* const dec) {

  dec->cache_id = 0;

  if (dec->mt_method > 0) {

    WebPWorker* const worker = &dec->worker;

    if (!WebPGetWorkerInterface()->Reset(worker)) {

      return VP8SetError(dec, VP8_STATUS_OUT_OF_MEMORY,

                         "thread initialization failed.");

    }

    worker->data1 = dec;

    worker->data2 = (void*)&dec->thread_ctx.io;

    worker->hook = FinishRow;

    dec->num_caches =

        (dec->filter_type > 0) ? MT_CACHE_LINES : MT_CACHE_LINES - 1;

  } else {

    dec->num_caches = ST_CACHE_LINES;

  }

  return 1;

}

int VP8GetThreadMethod(const WebPDecoderOptions* const options,

                       const WebPHeaderStructure* const headers, int width,

                       int height) {

  if (options == NULL || options->use_threads == 0) {

    return 0;

  }

  (void)headers;

  (void)width;

  (void)height;

  assert(headers == NULL || !headers->is_lossless);

#if defined(WEBP_USE_THREAD)

  if (width >= MIN_WIDTH_FOR_THREADS) return 2;

#endif

  return 0;

}

#undef MT_CACHE_LINES

#undef ST_CACHE_LINES

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

// Memory setup

static int AllocateMemory(VP8Decoder* const dec) {

  const int num_caches = dec->num_caches;

  const int mb_w = dec->mb_w;

  // Note: we use 'size_t' when there's no overflow risk, uint64_t otherwise.

  const size_t intra_pred_mode_size = 4 * mb_w * sizeof(uint8_t);

  const size_t top_size = sizeof(VP8TopSamples) * mb_w;

  const size_t mb_info_size = (mb_w + 1) * sizeof(VP8MB);

  const size_t f_info_size =

      (dec->filter_type > 0)

          ? mb_w * (dec->mt_method > 0 ? 2 : 1) * sizeof(VP8FInfo)

          : 0;

  const size_t yuv_size = YUV_SIZE * sizeof(*dec->yuv_b);

  const size_t mb_data_size =

      (dec->mt_method == 2 ? 2 : 1) * mb_w * sizeof(*dec->mb_data);

  const size_t cache_height =

      (16 * num_caches + kFilterExtraRows[dec->filter_type]) * 3 / 2;

  const size_t cache_size = top_size * cache_height;

  // alpha_size is the only one that scales as width x height.

  const uint64_t alpha_size =

      (dec->alpha_data != NULL)

          ? (uint64_t)dec->pic_hdr.width * dec->pic_hdr.height

          : 0ULL;

  const uint64_t needed = (uint64_t)intra_pred_mode_size + top_size +

                          mb_info_size + f_info_size + yuv_size + mb_data_size +

                          cache_size + alpha_size + WEBP_ALIGN_CST;

  uint8_t* mem;

  if (!CheckSizeOverflow(needed)) return 0;  // check for overflow

  if (needed > dec->mem_size) {

    WebPSafeFree(dec->mem);

    dec->mem_size = 0;

    dec->mem = WebPSafeMalloc(needed, sizeof(uint8_t));

    if (dec->mem == NULL) {

      return VP8SetError(dec, VP8_STATUS_OUT_OF_MEMORY,

                         "no memory during frame initialization.");

    }

    // down-cast is ok, thanks to WebPSafeMalloc() above.

    dec->mem_size = (size_t)needed;

  }

  mem = (uint8_t*)dec->mem;

  dec->intra_t = mem;

  mem += intra_pred_mode_size;

  dec->yuv_t = (VP8TopSamples*)mem;

  mem += top_size;

  dec->mb_info = ((VP8MB*)mem) + 1;

  mem += mb_info_size;

  dec->f_info = f_info_size ? (VP8FInfo*)mem : NULL;

  mem += f_info_size;

  dec->thread_ctx.id = 0;

  dec->thread_ctx.f_info = dec->f_info;

  if (dec->filter_type > 0 && dec->mt_method > 0) {

    // secondary cache line. The deblocking process need to make use of the

    // filtering strength from previous macroblock row, while the new ones

    // are being decoded in parallel. We'll just swap the pointers.

    dec->thread_ctx.f_info += mb_w;

  }

  mem = (uint8_t*)WEBP_ALIGN(mem);

  assert((yuv_size & WEBP_ALIGN_CST) == 0);

  dec->yuv_b = mem;

  mem += yuv_size;

  dec->mb_data = (VP8MBData*)mem;

  dec->thread_ctx.mb_data = (VP8MBData*)mem;

  if (dec->mt_method == 2) {

    dec->thread_ctx.mb_data += mb_w;

  }

  mem += mb_data_size;

  dec->cache_y_stride = 16 * mb_w;

  dec->cache_uv_stride = 8 * mb_w;

  {

    const int extra_rows = kFilterExtraRows[dec->filter_type];

    const int extra_y = extra_rows * dec->cache_y_stride;

    const int extra_uv = (extra_rows / 2) * dec->cache_uv_stride;

    dec->cache_y = mem + extra_y;

    dec->cache_u =

        dec->cache_y + 16 * num_caches * dec->cache_y_stride + extra_uv;

    dec->cache_v =

        dec->cache_u + 8 * num_caches * dec->cache_uv_stride + extra_uv;

    dec->cache_id = 0;

  }

  mem += cache_size;

  // alpha plane

  dec->alpha_plane = alpha_size ? mem : NULL;

  mem += alpha_size;

  assert(mem <= (uint8_t*)dec->mem + dec->mem_size);

  // note: left/top-info is initialized once for all.

  WEBP_UNSAFE_MEMSET(dec->mb_info - 1, 0, mb_info_size);

  VP8InitScanline(dec);  // initialize left too.

  // initialize top

  WEBP_UNSAFE_MEMSET(dec->intra_t, B_DC_PRED, intra_pred_mode_size);

  return 1;

}

static void InitIo(VP8Decoder* const dec, VP8Io* io) {

  // prepare 'io'

  io->mb_y = 0;

  io->y = dec->cache_y;

  io->u = dec->cache_u;

  io->v = dec->cache_v;

  io->y_stride = dec->cache_y_stride;

  io->uv_stride = dec->cache_uv_stride;

  io->a = NULL;

}

int VP8InitFrame(VP8Decoder* const dec, VP8Io* const io) {

  if (!InitThreadContext(dec)) return 0;  // call first. Sets dec->num_caches.

  if (!AllocateMemory(dec)) return 0;

  InitIo(dec, io);

  VP8DspInit();  // Init critical function pointers and look-up tables.

  return 1;

}

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