Fix a FPE in CStretchEngine::StartStretchHorz().

core/fxge/dib/fx_dib_engine.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // 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 <limits.h>
 
 #include <algorithm>
 
@@ skipping 215 matching lines @@
       double weight = area_start >= area_end ? 0.0f : area_end - area_start;
       if (weight == 0 && j == end_i) {
         pixel_weights.m_SrcEnd--;
         break;
       }
       pixel_weights.m_Weights[j - start_i] =
           FXSYS_round((FX_FLOAT)(weight * 65536));
     }
   }
 }
+
 CStretchEngine::CStretchEngine(IFX_ScanlineComposer* pDestBitmap,
                                FXDIB_Format dest_format,
                                int dest_width,
                                int dest_height,
                                const FX_RECT& clip_rect,
                                const CFX_DIBSource* pSrcBitmap,
                                int flags) {
   m_State = 0;
   m_DestFormat = dest_format;
   m_DestBpp = dest_format & 0xff;
@@ skipping 91 matching lines @@
       }
     }
   } else {
     if (!m_bHasAlpha) {
       m_TransMethod = 7;
     } else {
       m_TransMethod = 8;
     }
   }
 }
+
+CStretchEngine::~CStretchEngine() {
+  FX_Free(m_pDestScanline);
+  FX_Free(m_pInterBuf);
+  FX_Free(m_pExtraAlphaBuf);
+  FX_Free(m_pDestMaskScanline);
+}
+
 FX_BOOL CStretchEngine::Continue(IFX_Pause* pPause) {
   while (m_State == 1) {
     if (ContinueStretchHorz(pPause)) {
       return TRUE;
     }
     m_State = 2;
     StretchVert();
   }
   return FALSE;
 }
-CStretchEngine::~CStretchEngine() {
-  FX_Free(m_pDestScanline);
-  FX_Free(m_pInterBuf);
-  FX_Free(m_pExtraAlphaBuf);
-  FX_Free(m_pDestMaskScanline);
-}
+
 FX_BOOL CStretchEngine::StartStretchHorz() {
-  if (m_DestWidth == 0 || !m_pDestScanline ||
-      m_SrcClip.Height() > (int)((1U << 29) / m_InterPitch) ||
-      m_SrcClip.Height() == 0) {
+  if (m_DestWidth == 0 || m_InterPitch == 0 || !m_pDestScanline)
+    return FALSE;
+
+  if (m_SrcClip.Height() == 0 ||
+      m_SrcClip.Height() > (1 << 29) / m_InterPitch) {
     return FALSE;
   }
+
   m_pInterBuf = FX_TryAlloc(unsigned char, m_SrcClip.Height() * m_InterPitch);
-  if (!m_pInterBuf) {
+  if (!m_pInterBuf)
     return FALSE;
-  }
+
   if (m_pSource && m_bHasAlpha && m_pSource->m_pAlphaMask) {
     m_pExtraAlphaBuf =
         FX_Alloc2D(unsigned char, m_SrcClip.Height(), m_ExtraMaskPitch);
     uint32_t size = (m_DestClip.Width() * 8 + 31) / 32 * 4;
     m_pDestMaskScanline = FX_TryAlloc(unsigned char, size);
-    if (!m_pDestMaskScanline) {
+    if (!m_pDestMaskScanline)
       return FALSE;
-    }
   }
   m_WeightTable.Calc(m_DestWidth, m_DestClip.left, m_DestClip.right, m_SrcWidth,
                      m_SrcClip.left, m_SrcClip.right, m_Flags);
-  if (!m_WeightTable.m_pWeightTables) {
+  if (!m_WeightTable.m_pWeightTables)
     return FALSE;
-  }
+
   m_CurRow = m_SrcClip.top;
   m_State = 1;
   return TRUE;
 }
-#define FX_STRECH_PAUSE_ROWS 10
+
 FX_BOOL CStretchEngine::ContinueStretchHorz(IFX_Pause* pPause) {
-  if (!m_DestWidth) {
-    return 0;
-  }
-  if (m_pSource->SkipToScanline(m_CurRow, pPause)) {
+  if (!m_DestWidth)
+    return FALSE;
+
+  if (m_pSource->SkipToScanline(m_CurRow, pPause))
     return TRUE;
-  }
+
   int Bpp = m_DestBpp / 8;
-  int rows_to_go = FX_STRECH_PAUSE_ROWS;
+  static const int kStrechPauseRows = 10;
+  int rows_to_go = kStrechPauseRows;
   for (; m_CurRow < m_SrcClip.bottom; m_CurRow++) {
     if (rows_to_go == 0) {
-      if (pPause && pPause->NeedToPauseNow()) {
+      if (pPause && pPause->NeedToPauseNow())
         return TRUE;
-      }
-      rows_to_go = FX_STRECH_PAUSE_ROWS;
+
+      rows_to_go = kStrechPauseRows;
     }
+
     const uint8_t* src_scan = m_pSource->GetScanline(m_CurRow);
     uint8_t* dest_scan =
         m_pInterBuf + (m_CurRow - m_SrcClip.top) * m_InterPitch;
     const uint8_t* src_scan_mask = nullptr;
     uint8_t* dest_scan_mask = nullptr;
     if (m_pExtraAlphaBuf) {
       src_scan_mask = m_pSource->m_pAlphaMask->GetScanline(m_CurRow);
       dest_scan_mask =
           m_pExtraAlphaBuf + (m_CurRow - m_SrcClip.top) * m_ExtraMaskPitch;
     }
@@ skipping 193 matching lines @@
           }
           dest_scan += Bpp - 3;
         }
         break;
       }
     }
     rows_to_go--;
   }
   return FALSE;
 }
+
 void CStretchEngine::StretchVert() {
-  if (m_DestHeight == 0) {
+  if (m_DestHeight == 0)
     return;
-  }
+
   CWeightTable table;
   table.Calc(m_DestHeight, m_DestClip.top, m_DestClip.bottom, m_SrcHeight,
              m_SrcClip.top, m_SrcClip.bottom, m_Flags);
-  if (!table.m_pWeightTables) {
+  if (!table.m_pWeightTables)
     return;
-  }
+
   int DestBpp = m_DestBpp / 8;
   for (int row = m_DestClip.top; row < m_DestClip.bottom; row++) {
     unsigned char* dest_scan = m_pDestScanline;
     unsigned char* dest_sacn_mask = m_pDestMaskScanline;
     PixelWeight* pPixelWeights = table.GetPixelWeight(row);
     switch (m_TransMethod) {
       case 1:
       case 2:
       case 3: {
         for (int col = m_DestClip.left; col < m_DestClip.right; col++) {
@@ skipping 279 matching lines @@
                                   result_width);
     if (m_pMaskScanline) {
       m_pSource->m_pAlphaMask->DownSampleScanline(
           src_y, m_pMaskScanline.get(), 1, m_DestWidth, m_bFlipX,
           m_ClipRect.left, result_width);
     }
     m_pDest->ComposeScanline(dest_y, m_pScanline.get(), m_pMaskScanline.get());
   }
   return FALSE;
 }