commit f741aa6b32d544ae004928012a4c98001990c0e7
author Lei Zhang <thestig@chromium.org> Mon May 20 19:13:44 2024 +0000
committer Pdfium LUCI CQ <pdfium-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon May 20 19:13:44 2024 +0000
tree 030972273d06b8de520b67bd56381f255754f935
parent ab4ed5df9771de7d2f91f01ef8da8af3d3d9edb2

Move switches out of inner loop in FlatePredictorScanlineDecoder

In GetNextLineWithoutPredictedPitch(), make the switch decision first
before running the loop, rather than every time in the loop. Add
CopyAndAdvanceLine() as a helper method to avoid repeating code.

Change-Id: I9fa99a9806c6088218b5d9da6b71abc06d8f7c39
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/119254
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Thomas Sepez <tsepez@google.com>

core/fxcodec/flate/flatemodule.cpp

diff --git a/core/fxcodec/flate/flatemodule.cpp b/core/fxcodec/flate/flatemodule.cpp
index 644b0f7..1714e26 100644
--- a/core/fxcodec/flate/flatemodule.cpp
+++ b/core/fxcodec/flate/flatemodule.cpp
@@ -647,6 +647,7 @@
  private:
   void GetNextLineWithPredictedPitch();
   void GetNextLineWithoutPredictedPitch();
+  size_t CopyAndAdvanceLine(size_t bytes_to_go);
 
   const PredictorType m_Predictor;
   int m_Colors = 0;
@@ -745,34 +746,40 @@
   const uint32_t row_size =
       fxge::CalculatePitch8OrDie(m_BitsPerComponent, m_Colors, m_Columns);
   const uint32_t bytes_per_pixel = (m_BitsPerComponent * m_Colors + 7) / 8;
-  while (bytes_to_go) {
-    switch (m_Predictor) {
-      case PredictorType::kPng: {
+  switch (m_Predictor) {
+    case PredictorType::kPng: {
+      while (bytes_to_go) {
         FlateOutput(m_pFlate.get(), m_PredictRaw);
         PNG_PredictLine(m_PredictBuffer, m_PredictRaw, m_LastLine, row_size,
                         bytes_per_pixel);
         fxcrt::spancpy(m_LastLine.span(), m_PredictBuffer.span());
-        break;
+        bytes_to_go = CopyAndAdvanceLine(bytes_to_go);
       }
-      case PredictorType::kFlate: {
+      break;
+    }
+    case PredictorType::kFlate: {
+      while (bytes_to_go) {
         FlateOutput(m_pFlate.get(), m_PredictBuffer);
         TIFF_PredictLine(m_PredictBuffer, m_BitsPerComponent, m_Colors,
                          m_Columns);
-        break;
+        bytes_to_go = CopyAndAdvanceLine(bytes_to_go);
       }
-      case PredictorType::kNone: {
-        NOTREACHED_NORETURN();
-      }
+      break;
     }
-    size_t read_bytes =
-        m_PredictPitch > bytes_to_go ? bytes_to_go : m_PredictPitch;
-    fxcrt::spancpy(m_Scanline.subspan(m_Pitch - bytes_to_go),
-                   m_PredictBuffer.first(read_bytes));
-    m_LeftOver += m_PredictPitch - read_bytes;
-    bytes_to_go -= read_bytes;
+    case PredictorType::kNone: {
+      NOTREACHED_NORETURN();
+    }
   }
 }
 
+size_t FlatePredictorScanlineDecoder::CopyAndAdvanceLine(size_t bytes_to_go) {
+  size_t read_bytes = std::min<size_t>(m_PredictPitch, bytes_to_go);
+  fxcrt::spancpy(m_Scanline.subspan(m_Pitch - bytes_to_go),
+                 m_PredictBuffer.first(read_bytes));
+  m_LeftOver += m_PredictPitch - read_bytes;
+  return bytes_to_go - read_bytes;
+}
+
 }  // namespace
 
 // static