Switch to memcpy()/std::fill()/std::swap() in image processing code.

Use optimized library functions in more places.

Change-Id: I3a0ecb6d4e8a60b694dc4be58bd7379e5e5837a0
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/73031
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

core/fpdfapi/page/cpdf_dib.cpp

diff --git a/core/fpdfapi/page/cpdf_dib.cpp b/core/fpdfapi/page/cpdf_dib.cpp
index d1ab8c8..bf61337 100644
--- a/core/fpdfapi/page/cpdf_dib.cpp
+++ b/core/fpdfapi/page/cpdf_dib.cpp
@@ -731,9 +731,7 @@
         const uint8_t* src = result_bitmap->GetScanline(row);
         uint8_t* dest = rgb_bitmap->GetWritableScanline(row);
         for (uint32_t col = 0; col < image_info.width; ++col) {
-          dest[0] = src[0];
-          dest[1] = src[1];
-          dest[2] = src[2];
+          memcpy(dest, src, 3);
           src += 4;
           dest += 3;
         }
@@ -860,9 +858,8 @@
       return;
     }
     float color_values[3];
-    color_values[0] = m_CompData[0].m_DecodeMin;
-    color_values[1] = color_values[0];
-    color_values[2] = color_values[0];
+    std::fill(std::begin(color_values), std::end(color_values),
+              m_CompData[0].m_DecodeMin);
 
     float R = 0.0f;
     float G = 0.0f;

core/fxcodec/fx_codec.cpp

diff --git a/core/fxcodec/fx_codec.cpp b/core/fxcodec/fx_codec.cpp
index 300a0a5..84f386a 100644
--- a/core/fxcodec/fx_codec.cpp
+++ b/core/fxcodec/fx_codec.cpp
@@ -6,6 +6,8 @@
 
 #include "core/fxcodec/fx_codec.h"
 
+#include <algorithm>
+
 #include "core/fxcrt/fx_memory.h"
 
 namespace fxcodec {
@@ -22,9 +24,7 @@
 void ReverseRGB(uint8_t* pDestBuf, const uint8_t* pSrcBuf, int pixels) {
   if (pDestBuf == pSrcBuf) {
     for (int i = 0; i < pixels; i++) {
-      uint8_t temp = pDestBuf[2];
-      pDestBuf[2] = pDestBuf[0];
-      pDestBuf[0] = temp;
+      std::swap(pDestBuf[0], pDestBuf[2]);
       pDestBuf += 3;
     }
   } else {

testing/image_diff/image_diff_png.cpp

diff --git a/testing/image_diff/image_diff_png.cpp b/testing/image_diff/image_diff_png.cpp
index dcd9d69..e035ec6 100644
--- a/testing/image_diff/image_diff_png.cpp
+++ b/testing/image_diff/image_diff_png.cpp
@@ -92,12 +92,12 @@
                       int pixel_width,
                       uint8_t* rgb,
                       bool* is_opaque) {
+  const uint8_t* pixel_in = rgba;
+  uint8_t* pixel_out = rgb;
   for (int x = 0; x < pixel_width; x++) {
-    const uint8_t* pixel_in = &rgba[x * 4];
-    uint8_t* pixel_out = &rgb[x * 3];
-    pixel_out[0] = pixel_in[0];
-    pixel_out[1] = pixel_in[1];
-    pixel_out[2] = pixel_in[2];
+    memcpy(pixel_out, pixel_in, 3);
+    pixel_in += 4;
+    pixel_out += 3;
   }
 }
 
@@ -148,13 +148,13 @@
                       int pixel_width,
                       uint8_t* rgba,
                       bool* is_opaque) {
+  const uint8_t* pixel_in = rgb;
+  uint8_t* pixel_out = rgba;
   for (int x = 0; x < pixel_width; x++) {
-    const uint8_t* pixel_in = &rgb[x * 3];
-    uint8_t* pixel_out = &rgba[x * 4];
-    pixel_out[0] = pixel_in[0];
-    pixel_out[1] = pixel_in[1];
-    pixel_out[2] = pixel_in[2];
+    memcpy(pixel_out, pixel_in, 3);
     pixel_out[3] = 0xff;
+    pixel_in += 3;
+    pixel_out += 4;
   }
 }