Add an appropriate fallback to hb_int_mul_overflows

src/hb-algs.hh

@@ -645,16 +645,17 @@ hb_unsigned_mul_overflows (unsigned int count, unsigned int size)
   return (size > 0) && (count >= ((unsigned int) -1) / size);
 }
 
-/* Right now we only have one use for signed overflow and as it
- * is GCC 5.1 > and clang we don't care about its fallback ATM */
-#ifndef __has_builtin
-# define __has_builtin(x) 0
-#endif
+static inline bool
+hb_int_mul_overflows (int x, int y, int &result)
+{
 #if __has_builtin(__builtin_mul_overflow)
-# define hb_signed_mul_overflows(x, y, result) __builtin_mul_overflow(x, y, &result)
+  return __builtin_mul_overflow (x, y, &result);
 #else
-# define hb_signed_mul_overflows(x, y, result) (result = (x) * (y), false)
+  int64_t sink = (int64_t) x * y;
+  result = sink;
+  return result != sink;
 #endif
+}
 
 
 /*

src/hb-ot-var-avar-table.hh

@@ -90,9 +90,9 @@ struct SegmentMaps : ArrayOf<AxisValueMap>
       return arrayZ[i-1].toCoord;
 
     int factor;
-    if (hb_signed_mul_overflows (arrayZ[i].toCoord - arrayZ[i-1].toCoord,
-				 value - arrayZ[i-1].fromCoord,
-				 factor))
+    if (unlikely (hb_int_mul_overflows (arrayZ[i].toCoord - arrayZ[i-1].toCoord,
+					value - arrayZ[i-1].fromCoord,
+					factor)))
       return arrayZ[i-1].toCoord;
 
     int denom = arrayZ[i].fromCoord - arrayZ[i-1].fromCoord;

src/hb.hh

@@ -219,6 +219,10 @@ extern "C" void  hb_free_impl(void *ptr);
  * Compiler attributes
  */
 
+#ifndef __has_builtin
+# define __has_builtin(x) 0
+#endif
+
 #if (defined(__GNUC__) || defined(__clang__)) && defined(__OPTIMIZE__)
 #define likely(expr) (__builtin_expect (!!(expr), 1))
 #define unlikely(expr) (__builtin_expect (!!(expr), 0))