Odd width variation of scale down by 2 for subsampling

source/scale_common.cc

Index: source/scale_common.cc
diff --git a/source/scale_common.cc b/source/scale_common.cc
index f5c908d0bf5b4d41d2d44b34d29e65a9ed859b61..30ff18c50750b06e9e3488fd8c38a5218ee429db 100644
--- a/source/scale_common.cc
+++ b/source/scale_common.cc
@@ -103,6 +103,28 @@ void ScaleRowDown2Box_C(const uint8* src_ptr, ptrdiff_t src_stride,
   }
 }
 
+void ScaleRowDown2Box_Odd_C(const uint8* src_ptr, ptrdiff_t src_stride,
+                            uint8* dst, int dst_width) {
+  const uint8* s = src_ptr;
+  const uint8* t = src_ptr + src_stride;
+  int x;
+  dst_width -= 1;
+  for (x = 0; x < dst_width - 1; x += 2) {
+    dst[0] = (s[0] + s[1] + t[0] + t[1] + 2) >> 2;
+    dst[1] = (s[2] + s[3] + t[2] + t[3] + 2) >> 2;
+    dst += 2;
+    s += 4;
+    t += 4;
+  }
+  if (dst_width & 1) {
+    dst[0] = (s[0] + s[1] + t[0] + t[1] + 2) >> 2;
+    dst += 1;
+    s += 2;
+    t += 2;
+  }
+  dst[0] = (s[0] + t[0] + 1) >> 1;
+}
+
 void ScaleRowDown2Box_16_C(const uint16* src_ptr, ptrdiff_t src_stride,
                            uint16* dst, int dst_width) {
   const uint16* s = src_ptr;