webkitgtk-2.16.5HEADwebkitgtk-2.16.5master

1 files changed, 46 insertions, 8 deletions

diff --git a/Source/WTF/wtf/SaturatedArithmetic.h b/Source/WTF/wtf/SaturatedArithmetic.h
index cf9e8e17e..516e3bcbb 100644
--- a/Source/WTF/wtf/SaturatedArithmetic.h
+++ b/Source/WTF/wtf/SaturatedArithmetic.h
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2012, Google Inc. All rights reserved.
+ * Copyright (C) 2014 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ -31,35 +32,72 @@
 #ifndef SaturatedArithmetic_h
 #define SaturatedArithmetic_h
 
+#include "Compiler.h"
 #include <limits>
 #include <stdint.h>
 #include <stdlib.h>
 
-inline int32_t saturatedAddition(int32_t a, int32_t b)
+inline bool signedAddOverflows(int32_t a, int32_t b, int32_t& result)
 {
+#if COMPILER_HAS_CLANG_BUILTIN(__builtin_sadd_overflow) && !(defined __clang_major__ && __clang_major__ < 7)
+    return __builtin_sadd_overflow(a, b, &result);
+#else
     uint32_t ua = a;
     uint32_t ub = b;
-    uint32_t result = ua + ub;
+    uint32_t uresult = ua + ub;
+    result = static_cast<int32_t>(uresult);
 
     // Can only overflow if the signed bit of the two values match. If the signed
     // bit of the result and one of the values differ it did overflow.
-    if (!((ua ^ ub) >> 31) & (result ^ ua) >> 31)
-        result = std::numeric_limits<int>::max() + (ua >> 31);
+    return !((ua ^ ub) >> 31) && (uresult ^ ua) >> 31;
+#endif
+}
 
+inline int32_t saturatedAddition(int32_t a, int32_t b)
+{
+    int32_t result;
+#if CPU(ARM_THUMB2)
+    asm("qadd %[sum], %[addend], %[augend]"
+        : [sum]"=r"(result)
+        : [augend]"r"(a), [addend]"r"(b)
+        : /* Nothing is clobbered. */
+        );
+#else
+    if (signedAddOverflows(a, b, result))
+        result = std::numeric_limits<int32_t>::max() + (static_cast<uint32_t>(a) >> 31);
+#endif
     return result;
 }
 
-inline int32_t saturatedSubtraction(int32_t a, int32_t b)
+inline bool signedSubtractOverflows(int32_t a, int32_t b, int32_t& result)
 {
+#if COMPILER_HAS_CLANG_BUILTIN(__builtin_ssub_overflow) && !(defined __clang_major__ && __clang_major__ < 7)
+    return __builtin_ssub_overflow(a, b, &result);
+#else
     uint32_t ua = a;
     uint32_t ub = b;
-    uint32_t result = ua - ub;
+    uint32_t uresult = ua - ub;
+    result = static_cast<int32_t>(uresult);
 
     // Can only overflow if the signed bit of the two values do not match. If the
     // signed bit of the result and the first value differ it did overflow.
-    if ((ua ^ ub) >> 31 & (result ^ ua) >> 31)
-        result = std::numeric_limits<int>::max() + (ua >> 31);
+    return (ua ^ ub) >> 31 && (uresult ^ ua) >> 31;
+#endif
+}
 
+inline int32_t saturatedSubtraction(int32_t a, int32_t b)
+{
+    int32_t result;
+#if CPU(ARM_THUMB2)
+    asm("qsub %[difference], %[minuend], %[subtrahend]"
+        : [difference]"=r"(result)
+        : [minuend]"r"(a), [subtrahend]"r"(b)
+        : /* Nothing is clobbered. */
+        );
+#else
+    if (signedSubtractOverflows(a, b, result))
+        result = std::numeric_limits<int32_t>::max() + (static_cast<uint32_t>(a) >> 31);
+#endif
     return result;
 }