planar blend use signed images

source/row_common.cc

 /*
  *  Copyright 2011 The LibYuv Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE 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.
  */
 
@@ skipping 1998 matching lines @@
     uint32 bb = src_argb1[0];
     uint32 bg = src_argb1[1];
     uint32 br = src_argb1[2];
     dst_argb[0] = BLEND(fb, bb, a);
     dst_argb[1] = BLEND(fg, bg, a);
     dst_argb[2] = BLEND(fr, br, a);
     dst_argb[3] = 255u;
   }
 }
 #undef BLEND
+
+void BlendPlaneRow_C(const uint8* src0, const uint8* src1,
+                     const uint8* alpha, uint8* dst, int width) {
+  int x;
+  for (x = 0; x < width; ++x) {
+    uint32 f = *src0++;
+    uint32 b = *src1++;
+    uint32 a = *alpha++;
+    *dst++ = (((a) * f) + ((255 - a) * b) + 255) >> 8;
+  }
+}
+
 #define ATTENUATE(f, a) (a | (a << 8)) * (f | (f << 8)) >> 24
 
 // Multiply source RGB by alpha and store to destination.
 // This code mimics the SSSE3 version for better testability.
 void ARGBAttenuateRow_C(const uint8* src_argb, uint8* dst_argb, int width) {
   int i;
   for (i = 0; i < width - 1; i += 2) {
     uint32 b = src_argb[0];
     uint32 g = src_argb[1];
     uint32 r = src_argb[2];
@@ skipping 582 matching lines @@
     dst_rgb565 += twidth * 2;
     width -= twidth;
   }
 }
 #endif
 
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
 #endif