// Copyright 2015 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com

#include "core/fxcodec/jbig2/JBig2_GrrdProc.h"

#include <memory>

#include "core/fxcodec/jbig2/JBig2_ArithDecoder.h"
#include "core/fxcodec/jbig2/JBig2_BitStream.h"
#include "core/fxcodec/jbig2/JBig2_Image.h"
#include "core/fxcrt/compiler_specific.h"

CJBig2_GRRDProc::CJBig2_GRRDProc() = default;

CJBig2_GRRDProc::~CJBig2_GRRDProc() = default;

std::unique_ptr<CJBig2_Image> CJBig2_GRRDProc::Decode(
    CJBig2_ArithDecoder* pArithDecoder,
    pdfium::span<JBig2ArithCtx> grContexts) {
  if (!CJBig2_Image::IsValidImageSize(GRW, GRH))
    return std::make_unique<CJBig2_Image>(GRW, GRH);

  if (!GRTEMPLATE) {
    if ((GRAT[0] == -1) && (GRAT[1] == -1) && (GRAT[2] == -1) &&
        (GRAT[3] == -1) && (GRREFERENCEDX == 0) &&
        (GRW == (uint32_t)GRREFERENCE->width())) {
      return DecodeTemplate0Opt(pArithDecoder, grContexts);
    }
    return DecodeTemplate0Unopt(pArithDecoder, grContexts);
  }

  if ((GRREFERENCEDX == 0) && (GRW == (uint32_t)GRREFERENCE->width()))
    return DecodeTemplate1Opt(pArithDecoder, grContexts);

  return DecodeTemplate1Unopt(pArithDecoder, grContexts);
}

std::unique_ptr<CJBig2_Image> CJBig2_GRRDProc::DecodeTemplate0Unopt(
    CJBig2_ArithDecoder* pArithDecoder,
    pdfium::span<JBig2ArithCtx> grContexts) {
  auto GRREG = std::make_unique<CJBig2_Image>(GRW, GRH);
  if (!GRREG->data())
    return nullptr;

  GRREG->Fill(false);
  int LTP = 0;
  for (uint32_t h = 0; h < GRH; h++) {
    if (TPGRON) {
      if (pArithDecoder->IsComplete()) {
        return nullptr;
      }
      LTP = LTP ^ pArithDecoder->Decode(&grContexts[0x0010]);
    }
    uint32_t lines[5];
    lines[0] = GRREG->GetPixel(1, h - 1);
    lines[0] |= GRREG->GetPixel(0, h - 1) << 1;
    lines[1] = 0;
    lines[2] = GRREFERENCE->GetPixel(-GRREFERENCEDX + 1, h - GRREFERENCEDY - 1);
    lines[2] |= GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY - 1)
                << 1;
    lines[3] = GRREFERENCE->GetPixel(-GRREFERENCEDX + 1, h - GRREFERENCEDY);
    lines[3] |= GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY) << 1;
    lines[3] |= GRREFERENCE->GetPixel(-GRREFERENCEDX - 1, h - GRREFERENCEDY)
                << 2;
    lines[4] = GRREFERENCE->GetPixel(-GRREFERENCEDX + 1, h - GRREFERENCEDY + 1);
    lines[4] |= GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY + 1)
                << 1;
    lines[4] |= GRREFERENCE->GetPixel(-GRREFERENCEDX - 1, h - GRREFERENCEDY + 1)
                << 2;
    if (!LTP) {
      for (uint32_t w = 0; w < GRW; w++) {
        uint32_t CONTEXT =
            DecodeTemplate0UnoptCalculateContext(*GRREG, lines, w, h);
        if (pArithDecoder->IsComplete())
          return nullptr;

        int bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
        DecodeTemplate0UnoptSetPixel(GRREG.get(), lines, w, h, bVal);
      }
    } else {
      for (uint32_t w = 0; w < GRW; w++) {
        int bVal = GRREFERENCE->GetPixel(w, h);
        if (!(TPGRON && (bVal == GRREFERENCE->GetPixel(w - 1, h - 1)) &&
              (bVal == GRREFERENCE->GetPixel(w, h - 1)) &&
              (bVal == GRREFERENCE->GetPixel(w + 1, h - 1)) &&
              (bVal == GRREFERENCE->GetPixel(w - 1, h)) &&
              (bVal == GRREFERENCE->GetPixel(w + 1, h)) &&
              (bVal == GRREFERENCE->GetPixel(w - 1, h + 1)) &&
              (bVal == GRREFERENCE->GetPixel(w, h + 1)) &&
              (bVal == GRREFERENCE->GetPixel(w + 1, h + 1)))) {
          uint32_t CONTEXT =
              DecodeTemplate0UnoptCalculateContext(*GRREG, lines, w, h);
          if (pArithDecoder->IsComplete())
            return nullptr;

          bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
        }
        DecodeTemplate0UnoptSetPixel(GRREG.get(), lines, w, h, bVal);
      }
    }
  }
  return GRREG;
}

uint32_t CJBig2_GRRDProc::DecodeTemplate0UnoptCalculateContext(
    const CJBig2_Image& GRREG,
    const uint32_t* lines,
    uint32_t w,
    uint32_t h) const {
  UNSAFE_TODO({
    uint32_t CONTEXT = lines[4];
    CONTEXT |= lines[3] << 3;
    CONTEXT |= lines[2] << 6;
    CONTEXT |= GRREFERENCE->GetPixel(w - GRREFERENCEDX + GRAT[2],
                                     h - GRREFERENCEDY + GRAT[3])
               << 8;
    CONTEXT |= lines[1] << 9;
    CONTEXT |= lines[0] << 10;
    CONTEXT |= GRREG.GetPixel(w + GRAT[0], h + GRAT[1]) << 12;
    return CONTEXT;
  });
}

void CJBig2_GRRDProc::DecodeTemplate0UnoptSetPixel(CJBig2_Image* GRREG,
                                                   uint32_t* lines,
                                                   uint32_t w,
                                                   uint32_t h,
                                                   int bVal) {
  GRREG->SetPixel(w, h, bVal);
  UNSAFE_TODO({
    lines[0] = ((lines[0] << 1) | GRREG->GetPixel(w + 2, h - 1)) & 0x03;
    lines[1] = ((lines[1] << 1) | bVal) & 0x01;
    lines[2] =
        ((lines[2] << 1) |
         GRREFERENCE->GetPixel(w - GRREFERENCEDX + 2, h - GRREFERENCEDY - 1)) &
        0x03;
    lines[3] = ((lines[3] << 1) | GRREFERENCE->GetPixel(w - GRREFERENCEDX + 2,
                                                        h - GRREFERENCEDY)) &
               0x07;
    lines[4] =
        ((lines[4] << 1) |
         GRREFERENCE->GetPixel(w - GRREFERENCEDX + 2, h - GRREFERENCEDY + 1)) &
        0x07;
  });
}

std::unique_ptr<CJBig2_Image> CJBig2_GRRDProc::DecodeTemplate0Opt(
    CJBig2_ArithDecoder* pArithDecoder,
    pdfium::span<JBig2ArithCtx> grContexts) {
  if (!GRREFERENCE->data())
    return nullptr;

  int32_t iGRW = static_cast<int32_t>(GRW);
  int32_t iGRH = static_cast<int32_t>(GRH);
  auto GRREG = std::make_unique<CJBig2_Image>(iGRW, iGRH);
  if (!GRREG->data())
    return nullptr;

  int LTP = 0;
  uint8_t* pLine = GRREG->data();
  uint8_t* pLineR = GRREFERENCE->data();
  intptr_t nStride = GRREG->stride();
  intptr_t nStrideR = GRREFERENCE->stride();
  int32_t GRWR = GRREFERENCE->width();
  int32_t GRHR = GRREFERENCE->height();
  if (GRREFERENCEDY < -GRHR + 1 || GRREFERENCEDY > GRHR - 1)
    GRREFERENCEDY = 0;
  intptr_t nOffset = -GRREFERENCEDY * nStrideR;
  for (int32_t h = 0; h < iGRH; h++) {
    if (TPGRON) {
      if (pArithDecoder->IsComplete()) {
        return nullptr;
      }
      LTP = LTP ^ pArithDecoder->Decode(&grContexts[0x0010]);
    }
    uint32_t line1 = (h > 0) ? UNSAFE_TODO(pLine[-nStride]) << 4 : 0;
    int32_t reference_h = h - GRREFERENCEDY;
    bool line1_r_ok = (reference_h > 0 && reference_h < GRHR + 1);
    bool line2_r_ok = (reference_h > -1 && reference_h < GRHR);
    bool line3_r_ok = (reference_h > -2 && reference_h < GRHR - 1);
    uint32_t line1_r = line1_r_ok ? UNSAFE_TODO(pLineR[nOffset - nStrideR]) : 0;
    uint32_t line2_r = line2_r_ok ? UNSAFE_TODO(pLineR[nOffset]) : 0;
    uint32_t line3_r = line3_r_ok ? UNSAFE_TODO(pLineR[nOffset + nStrideR]) : 0;
    if (!LTP) {
      uint32_t CONTEXT = (line1 & 0x1c00) | (line1_r & 0x01c0) |
                         ((line2_r >> 3) & 0x0038) | ((line3_r >> 6) & 0x0007);
      for (int32_t w = 0; w < iGRW; w += 8) {
        int32_t nBits = iGRW - w > 8 ? 8 : iGRW - w;
        if (h > 0) {
          line1 =
              (line1 << 8) |
              (w + 8 < iGRW ? UNSAFE_TODO(pLine[-nStride + (w >> 3) + 1]) << 4
                            : 0);
        }
        if (h > GRHR + GRREFERENCEDY + 1) {
          line1_r = 0;
          line2_r = 0;
          line3_r = 0;
        } else {
          if (line1_r_ok) {
            line1_r =
                (line1_r << 8) |
                (w + 8 < GRWR
                     ? UNSAFE_TODO(pLineR[nOffset - nStrideR + (w >> 3) + 1])
                     : 0);
          }
          if (line2_r_ok) {
            line2_r =
                (line2_r << 8) |
                (w + 8 < GRWR ? UNSAFE_TODO(pLineR[nOffset + (w >> 3) + 1])
                              : 0);
          }
          if (line3_r_ok) {
            line3_r =
                (line3_r << 8) |
                (w + 8 < GRWR
                     ? UNSAFE_TODO(pLineR[nOffset + nStrideR + (w >> 3) + 1])
                     : 0);
          } else {
            line3_r = 0;
          }
        }
        uint8_t cVal = 0;
        for (int32_t k = 0; k < nBits; k++) {
          int bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
          cVal |= bVal << (7 - k);
          CONTEXT = ((CONTEXT & 0x0cdb) << 1) | (bVal << 9) |
                    ((line1 >> (7 - k)) & 0x0400) |
                    ((line1_r >> (7 - k)) & 0x0040) |
                    ((line2_r >> (10 - k)) & 0x0008) |
                    ((line3_r >> (13 - k)) & 0x0001);
        }
        UNSAFE_TODO(pLine[w >> 3] = cVal);
      }
    } else {
      uint32_t CONTEXT = (line1 & 0x1c00) | (line1_r & 0x01c0) |
                         ((line2_r >> 3) & 0x0038) | ((line3_r >> 6) & 0x0007);
      for (int32_t w = 0; w < iGRW; w += 8) {
        int32_t nBits = iGRW - w > 8 ? 8 : iGRW - w;
        if (h > 0) {
          line1 =
              (line1 << 8) |
              (w + 8 < iGRW ? UNSAFE_TODO(pLine[-nStride + (w >> 3) + 1]) << 4
                            : 0);
        }
        if (line1_r_ok) {
          line1_r =
              (line1_r << 8) |
              (w + 8 < GRWR
                   ? UNSAFE_TODO(pLineR[nOffset - nStrideR + (w >> 3) + 1])
                   : 0);
        }
        if (line2_r_ok) {
          line2_r =
              (line2_r << 8) |
              (w + 8 < GRWR ? UNSAFE_TODO(pLineR[nOffset + (w >> 3) + 1]) : 0);
        }
        if (line3_r_ok) {
          line3_r =
              (line3_r << 8) |
              (w + 8 < GRWR
                   ? UNSAFE_TODO(pLineR[nOffset + nStrideR + (w >> 3) + 1])
                   : 0);
        } else {
          line3_r = 0;
        }
        uint8_t cVal = 0;
        for (int32_t k = 0; k < nBits; k++) {
          int bVal = GRREFERENCE->GetPixel(w + k, h);
          if (!(TPGRON && (bVal == GRREFERENCE->GetPixel(w + k - 1, h - 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k, h - 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k + 1, h - 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k - 1, h)) &&
                (bVal == GRREFERENCE->GetPixel(w + k + 1, h)) &&
                (bVal == GRREFERENCE->GetPixel(w + k - 1, h + 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k, h + 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k + 1, h + 1)))) {
            if (pArithDecoder->IsComplete())
              return nullptr;

            bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
          }
          cVal |= bVal << (7 - k);
          CONTEXT = ((CONTEXT & 0x0cdb) << 1) | (bVal << 9) |
                    ((line1 >> (7 - k)) & 0x0400) |
                    ((line1_r >> (7 - k)) & 0x0040) |
                    ((line2_r >> (10 - k)) & 0x0008) |
                    ((line3_r >> (13 - k)) & 0x0001);
        }
        UNSAFE_TODO(pLine[w >> 3] = cVal);
      }
    }
    UNSAFE_TODO(pLine += nStride);
    if (h < GRHR + GRREFERENCEDY) {
      UNSAFE_TODO(pLineR += nStrideR);
    }
  }
  return GRREG;
}

std::unique_ptr<CJBig2_Image> CJBig2_GRRDProc::DecodeTemplate1Unopt(
    CJBig2_ArithDecoder* pArithDecoder,
    pdfium::span<JBig2ArithCtx> grContexts) {
  auto GRREG = std::make_unique<CJBig2_Image>(GRW, GRH);
  if (!GRREG->data())
    return nullptr;

  GRREG->Fill(false);
  int LTP = 0;
  for (uint32_t h = 0; h < GRH; h++) {
    if (TPGRON) {
      if (pArithDecoder->IsComplete()) {
        return nullptr;
      }
      LTP = LTP ^ pArithDecoder->Decode(&grContexts[0x0008]);
    }
    if (!LTP) {
      uint32_t line1 = GRREG->GetPixel(1, h - 1);
      line1 |= GRREG->GetPixel(0, h - 1) << 1;
      line1 |= GRREG->GetPixel(-1, h - 1) << 2;
      uint32_t line2 = 0;
      uint32_t line3 =
          GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY - 1);
      uint32_t line4 =
          GRREFERENCE->GetPixel(-GRREFERENCEDX + 1, h - GRREFERENCEDY);
      line4 |= GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY) << 1;
      line4 |= GRREFERENCE->GetPixel(-GRREFERENCEDX - 1, h - GRREFERENCEDY)
               << 2;
      uint32_t line5 =
          GRREFERENCE->GetPixel(-GRREFERENCEDX + 1, h - GRREFERENCEDY + 1);
      line5 |= GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY + 1)
               << 1;
      for (uint32_t w = 0; w < GRW; w++) {
        uint32_t CONTEXT = line5;
        CONTEXT |= line4 << 2;
        CONTEXT |= line3 << 5;
        CONTEXT |= line2 << 6;
        CONTEXT |= line1 << 7;
        if (pArithDecoder->IsComplete()) {
          return nullptr;
        }
        int bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
        GRREG->SetPixel(w, h, bVal);
        line1 = ((line1 << 1) | GRREG->GetPixel(w + 2, h - 1)) & 0x07;
        line2 = ((line2 << 1) | bVal) & 0x01;
        line3 = ((line3 << 1) | GRREFERENCE->GetPixel(w - GRREFERENCEDX + 1,
                                                      h - GRREFERENCEDY - 1)) &
                0x01;
        line4 = ((line4 << 1) | GRREFERENCE->GetPixel(w - GRREFERENCEDX + 2,
                                                      h - GRREFERENCEDY)) &
                0x07;
        line5 = ((line5 << 1) | GRREFERENCE->GetPixel(w - GRREFERENCEDX + 2,
                                                      h - GRREFERENCEDY + 1)) &
                0x03;
      }
    } else {
      uint32_t line1 = GRREG->GetPixel(1, h - 1);
      line1 |= GRREG->GetPixel(0, h - 1) << 1;
      line1 |= GRREG->GetPixel(-1, h - 1) << 2;
      uint32_t line2 = 0;
      uint32_t line3 =
          GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY - 1);
      uint32_t line4 =
          GRREFERENCE->GetPixel(-GRREFERENCEDX + 1, h - GRREFERENCEDY);
      line4 |= GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY) << 1;
      line4 |= GRREFERENCE->GetPixel(-GRREFERENCEDX - 1, h - GRREFERENCEDY)
               << 2;
      uint32_t line5 =
          GRREFERENCE->GetPixel(-GRREFERENCEDX + 1, h - GRREFERENCEDY + 1);
      line5 |= GRREFERENCE->GetPixel(-GRREFERENCEDX, h - GRREFERENCEDY + 1)
               << 1;
      for (uint32_t w = 0; w < GRW; w++) {
        int bVal = GRREFERENCE->GetPixel(w, h);
        if (!(TPGRON && (bVal == GRREFERENCE->GetPixel(w - 1, h - 1)) &&
              (bVal == GRREFERENCE->GetPixel(w, h - 1)) &&
              (bVal == GRREFERENCE->GetPixel(w + 1, h - 1)) &&
              (bVal == GRREFERENCE->GetPixel(w - 1, h)) &&
              (bVal == GRREFERENCE->GetPixel(w + 1, h)) &&
              (bVal == GRREFERENCE->GetPixel(w - 1, h + 1)) &&
              (bVal == GRREFERENCE->GetPixel(w, h + 1)) &&
              (bVal == GRREFERENCE->GetPixel(w + 1, h + 1)))) {
          uint32_t CONTEXT = line5;
          CONTEXT |= line4 << 2;
          CONTEXT |= line3 << 5;
          CONTEXT |= line2 << 6;
          CONTEXT |= line1 << 7;
          if (pArithDecoder->IsComplete()) {
            return nullptr;
          }
          bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
        }
        GRREG->SetPixel(w, h, bVal);
        line1 = ((line1 << 1) | GRREG->GetPixel(w + 2, h - 1)) & 0x07;
        line2 = ((line2 << 1) | bVal) & 0x01;
        line3 = ((line3 << 1) | GRREFERENCE->GetPixel(w - GRREFERENCEDX + 1,
                                                      h - GRREFERENCEDY - 1)) &
                0x01;
        line4 = ((line4 << 1) | GRREFERENCE->GetPixel(w - GRREFERENCEDX + 2,
                                                      h - GRREFERENCEDY)) &
                0x07;
        line5 = ((line5 << 1) | GRREFERENCE->GetPixel(w - GRREFERENCEDX + 2,
                                                      h - GRREFERENCEDY + 1)) &
                0x03;
      }
    }
  }
  return GRREG;
}

std::unique_ptr<CJBig2_Image> CJBig2_GRRDProc::DecodeTemplate1Opt(
    CJBig2_ArithDecoder* pArithDecoder,
    pdfium::span<JBig2ArithCtx> grContexts) {
  if (!GRREFERENCE->data())
    return nullptr;

  int32_t iGRW = static_cast<int32_t>(GRW);
  int32_t iGRH = static_cast<int32_t>(GRH);
  auto GRREG = std::make_unique<CJBig2_Image>(iGRW, iGRH);
  if (!GRREG->data())
    return nullptr;

  int LTP = 0;
  uint8_t* pLine = GRREG->data();
  uint8_t* pLineR = GRREFERENCE->data();
  intptr_t nStride = GRREG->stride();
  intptr_t nStrideR = GRREFERENCE->stride();
  int32_t GRWR = GRREFERENCE->width();
  int32_t GRHR = GRREFERENCE->height();
  if (GRREFERENCEDY < -GRHR + 1 || GRREFERENCEDY > GRHR - 1) {
    GRREFERENCEDY = 0;
  }
  intptr_t nOffset = -GRREFERENCEDY * nStrideR;
  for (int32_t h = 0; h < iGRH; h++) {
    if (TPGRON) {
      if (pArithDecoder->IsComplete())
        return nullptr;

      LTP = LTP ^ pArithDecoder->Decode(&grContexts[0x0008]);
    }
    uint32_t line1 = (h > 0) ? UNSAFE_TODO(pLine[-nStride]) << 1 : 0;
    int32_t reference_h = h - GRREFERENCEDY;
    bool line1_r_ok = (reference_h > 0 && reference_h < GRHR + 1);
    bool line2_r_ok = (reference_h > -1 && reference_h < GRHR);
    bool line3_r_ok = (reference_h > -2 && reference_h < GRHR - 1);
    uint32_t line1_r = line1_r_ok ? UNSAFE_TODO(pLineR[nOffset - nStrideR]) : 0;
    uint32_t line2_r = line2_r_ok ? UNSAFE_TODO(pLineR[nOffset]) : 0;
    uint32_t line3_r = line3_r_ok ? UNSAFE_TODO(pLineR[nOffset + nStrideR]) : 0;
    if (!LTP) {
      uint32_t CONTEXT = (line1 & 0x0380) | ((line1_r >> 2) & 0x0020) |
                         ((line2_r >> 4) & 0x001c) | ((line3_r >> 6) & 0x0003);
      for (int32_t w = 0; w < iGRW; w += 8) {
        int32_t nBits = iGRW - w > 8 ? 8 : iGRW - w;
        if (h > 0)
          line1 =
              (line1 << 8) |
              (w + 8 < iGRW ? UNSAFE_TODO(pLine[-nStride + (w >> 3) + 1]) << 1
                            : 0);
        if (line1_r_ok)
          line1_r =
              (line1_r << 8) |
              (w + 8 < GRWR
                   ? UNSAFE_TODO(pLineR[nOffset - nStrideR + (w >> 3) + 1])
                   : 0);
        if (line2_r_ok)
          line2_r =
              (line2_r << 8) |
              (w + 8 < GRWR ? UNSAFE_TODO(pLineR[nOffset + (w >> 3) + 1]) : 0);
        if (line3_r_ok) {
          line3_r =
              (line3_r << 8) |
              (w + 8 < GRWR
                   ? UNSAFE_TODO(pLineR[nOffset + nStrideR + (w >> 3) + 1])
                   : 0);
        } else {
          line3_r = 0;
        }
        uint8_t cVal = 0;
        for (int32_t k = 0; k < nBits; k++) {
          int bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
          cVal |= bVal << (7 - k);
          CONTEXT = ((CONTEXT & 0x018d) << 1) | (bVal << 6) |
                    ((line1 >> (7 - k)) & 0x0080) |
                    ((line1_r >> (9 - k)) & 0x0020) |
                    ((line2_r >> (11 - k)) & 0x0004) |
                    ((line3_r >> (13 - k)) & 0x0001);
        }
        UNSAFE_TODO(pLine[w >> 3] = cVal);
      }
    } else {
      uint32_t CONTEXT = (line1 & 0x0380) | ((line1_r >> 2) & 0x0020) |
                         ((line2_r >> 4) & 0x001c) | ((line3_r >> 6) & 0x0003);
      for (int32_t w = 0; w < iGRW; w += 8) {
        int32_t nBits = iGRW - w > 8 ? 8 : iGRW - w;
        if (h > 0)
          line1 =
              (line1 << 8) |
              (w + 8 < iGRW ? UNSAFE_TODO(pLine[-nStride + (w >> 3) + 1]) << 1
                            : 0);
        if (line1_r_ok)
          line1_r =
              (line1_r << 8) |
              (w + 8 < GRWR
                   ? UNSAFE_TODO(pLineR[nOffset - nStrideR + (w >> 3) + 1])
                   : 0);
        if (line2_r_ok)
          line2_r =
              (line2_r << 8) |
              (w + 8 < GRWR ? UNSAFE_TODO(pLineR[nOffset + (w >> 3) + 1]) : 0);
        if (line3_r_ok) {
          line3_r =
              (line3_r << 8) |
              (w + 8 < GRWR
                   ? UNSAFE_TODO(pLineR[nOffset + nStrideR + (w >> 3) + 1])
                   : 0);
        } else {
          line3_r = 0;
        }
        uint8_t cVal = 0;
        for (int32_t k = 0; k < nBits; k++) {
          int bVal = GRREFERENCE->GetPixel(w + k, h);
          if (!(TPGRON && (bVal == GRREFERENCE->GetPixel(w + k - 1, h - 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k, h - 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k + 1, h - 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k - 1, h)) &&
                (bVal == GRREFERENCE->GetPixel(w + k + 1, h)) &&
                (bVal == GRREFERENCE->GetPixel(w + k - 1, h + 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k, h + 1)) &&
                (bVal == GRREFERENCE->GetPixel(w + k + 1, h + 1)))) {
            if (pArithDecoder->IsComplete())
              return nullptr;

            bVal = pArithDecoder->Decode(&grContexts[CONTEXT]);
          }
          cVal |= bVal << (7 - k);
          CONTEXT = ((CONTEXT & 0x018d) << 1) | (bVal << 6) |
                    ((line1 >> (7 - k)) & 0x0080) |
                    ((line1_r >> (9 - k)) & 0x0020) |
                    ((line2_r >> (11 - k)) & 0x0004) |
                    ((line3_r >> (13 - k)) & 0x0001);
        }
        UNSAFE_TODO(pLine[w >> 3] = cVal);
      }
    }
    UNSAFE_TODO(pLine += nStride);
    if (h < GRHR + GRREFERENCEDY) {
      UNSAFE_TODO(pLineR += nStrideR);
    }
  }
  return GRREG;
}