fix asserts in SkMulDiv255Round, and add test

include/core/SkMath.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkMath_DEFINED
@@ skipping 121 matching lines @@
         }
     #else
         #define SkMulS16(x, y)  ((x) * (y))
     #endif
 #endif
 
 /**
  *  Return a*b/((1 << shift) - 1), rounding any fractional bits.
  *  Only valid if a and b are unsigned and <= 32767 and shift is > 0 and <= 8
  */
-static inline unsigned SkMul16ShiftRound(unsigned a, unsigned b, int shift) {
+static inline unsigned SkMul16ShiftRound(U16CPU a, U16CPU b, int shift) {
     SkASSERT(a <= 32767);
     SkASSERT(b <= 32767);
     SkASSERT(shift > 0 && shift <= 8);
     unsigned prod = SkMulS16(a, b) + (1 << (shift - 1));
     return (prod + (prod >> shift)) >> shift;
 }
 
 /**
- *  Return a*b/255, rounding any fractional bits. Only valid if both
- *  a and b are 0..255
+ *  Return a*b/255, rounding any fractional bits.
+ *  Only valid if a and b are unsigned and <= 32767.
  */
-static inline U8CPU SkMulDiv255Round(U8CPU a, U8CPU b) {
-    SkASSERT((uint8_t)a == a);
-    SkASSERT((uint8_t)b == b);
+static inline U8CPU SkMulDiv255Round(U16CPU a, U16CPU b) {
+    SkASSERT(a <= 32767);
+    SkASSERT(b <= 32767);
     unsigned prod = SkMulS16(a, b) + 128;
     return (prod + (prod >> 8)) >> 8;
 }
 
 #endif