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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/177729">177729</a></dd>
<dt>Author</dt> <dd>benjamin@webkit.org</dd>
<dt>Date</dt> <dd>2014-12-24 18:46:32 -0800 (Wed, 24 Dec 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Simplify saturated integer add/sub
https://bugs.webkit.org/show_bug.cgi?id=139854
Reviewed by Darin Adler.
* wtf/Compiler.h:
Make a wrapper for __has_builtin for compilers that do not support it.
* wtf/SaturatedArithmetic.h:
(saturatedAddition):
(saturatedSubtraction):
Use the builtins when possible instead of reinventing the wheel.
On ARMv7, use the saturated math instructions.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWTFChangeLog">trunk/Source/WTF/ChangeLog</a></li>
<li><a href="#trunkSourceWTFwtfCompilerh">trunk/Source/WTF/wtf/Compiler.h</a></li>
<li><a href="#trunkSourceWTFwtfSaturatedArithmetich">trunk/Source/WTF/wtf/SaturatedArithmetic.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWTFChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/ChangeLog (177728 => 177729)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/ChangeLog 2014-12-25 02:31:36 UTC (rev 177728)
+++ trunk/Source/WTF/ChangeLog 2014-12-25 02:46:32 UTC (rev 177729)
</span><span class="lines">@@ -1,3 +1,19 @@
</span><ins>+2014-12-24 Benjamin Poulain <benjamin@webkit.org>
+
+ Simplify saturated integer add/sub
+ https://bugs.webkit.org/show_bug.cgi?id=139854
+
+ Reviewed by Darin Adler.
+
+ * wtf/Compiler.h:
+ Make a wrapper for __has_builtin for compilers that do not support it.
+
+ * wtf/SaturatedArithmetic.h:
+ (saturatedAddition):
+ (saturatedSubtraction):
+ Use the builtins when possible instead of reinventing the wheel.
+ On ARMv7, use the saturated math instructions.
+
</ins><span class="cx"> 2014-12-23 Anders Carlsson <andersca@apple.com>
</span><span class="cx">
</span><span class="cx"> Move dynamic_objc_cast to RetainPtr.h
</span></span></pre></div>
<a id="trunkSourceWTFwtfCompilerh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/Compiler.h (177728 => 177729)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/Compiler.h 2014-12-25 02:31:36 UTC (rev 177728)
+++ trunk/Source/WTF/wtf/Compiler.h 2014-12-25 02:46:32 UTC (rev 177729)
</span><span class="lines">@@ -35,6 +35,13 @@
</span><span class="cx"> /* COMPILER_QUIRK() - whether the compiler being used to build the project requires a given quirk. */
</span><span class="cx"> #define COMPILER_QUIRK(WTF_COMPILER_QUIRK) (defined WTF_COMPILER_QUIRK_##WTF_COMPILER_QUIRK && WTF_COMPILER_QUIRK_##WTF_COMPILER_QUIRK)
</span><span class="cx">
</span><ins>+/* COMPILER_HAS_CLANG_BUILTIN() - wether the compiler supports a particular clang builtin. */
+#ifdef __has_builtin
+#define COMPILER_HAS_CLANG_BUILTIN(x) __has_builtin(x)
+#else
+#define COMPILER_HAS_CLANG_BUILTIN(x) 0
+#endif
+
</ins><span class="cx"> /* ==== COMPILER() - primary detection of the compiler being used to build the project, in alphabetical order ==== */
</span><span class="cx">
</span><span class="cx"> /* COMPILER(CLANG) - Clang */
</span></span></pre></div>
<a id="trunkSourceWTFwtfSaturatedArithmetich"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/SaturatedArithmetic.h (177728 => 177729)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/SaturatedArithmetic.h 2014-12-25 02:31:36 UTC (rev 177728)
+++ trunk/Source/WTF/wtf/SaturatedArithmetic.h 2014-12-25 02:46:32 UTC (rev 177729)
</span><span class="lines">@@ -1,5 +1,6 @@
</span><span class="cx"> /*
</span><span class="cx"> * Copyright (c) 2012, Google Inc. All rights reserved.
</span><ins>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
</ins><span class="cx"> *
</span><span class="cx"> * Redistribution and use in source and binary forms, with or without
</span><span class="cx"> * modification, are permitted provided that the following conditions are
</span><span class="lines">@@ -31,35 +32,72 @@
</span><span class="cx"> #ifndef SaturatedArithmetic_h
</span><span class="cx"> #define SaturatedArithmetic_h
</span><span class="cx">
</span><ins>+#include "Compiler.h"
</ins><span class="cx"> #include <limits>
</span><span class="cx"> #include <stdint.h>
</span><span class="cx"> #include <stdlib.h>
</span><span class="cx">
</span><del>-inline int32_t saturatedAddition(int32_t a, int32_t b)
</del><ins>+inline bool signedAddOverflows(int32_t a, int32_t b, int32_t& result)
</ins><span class="cx"> {
</span><ins>+#if COMPILER_HAS_CLANG_BUILTIN(__builtin_sadd_overflow)
+ return __builtin_sadd_overflow(a, b, &result);
+#else
</ins><span class="cx"> uint32_t ua = a;
</span><span class="cx"> uint32_t ub = b;
</span><del>- uint32_t result = ua + ub;
</del><ins>+ uint32_t uresult = ua + ub;
+ result = static_cast<int32_t>(uresult);
</ins><span class="cx">
</span><span class="cx"> // Can only overflow if the signed bit of the two values match. If the signed
</span><span class="cx"> // bit of the result and one of the values differ it did overflow.
</span><del>- if (!((ua ^ ub) >> 31) & (result ^ ua) >> 31)
- result = std::numeric_limits<int>::max() + (ua >> 31);
</del><ins>+ return !((ua ^ ub) >> 31) & (uresult ^ ua) >> 31;
+#endif
+}
</ins><span class="cx">
</span><ins>+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
</ins><span class="cx"> return result;
</span><span class="cx"> }
</span><span class="cx">
</span><del>-inline int32_t saturatedSubtraction(int32_t a, int32_t b)
</del><ins>+inline bool signedSubtractOverflows(int32_t a, int32_t b, int32_t& result)
</ins><span class="cx"> {
</span><ins>+#if COMPILER_HAS_CLANG_BUILTIN(__builtin_ssub_overflow)
+ return __builtin_ssub_overflow(a, b, &result);
+#else
</ins><span class="cx"> uint32_t ua = a;
</span><span class="cx"> uint32_t ub = b;
</span><del>- uint32_t result = ua - ub;
</del><ins>+ uint32_t uresult = ua - ub;
+ result = static_cast<int32_t>(uresult);
</ins><span class="cx">
</span><span class="cx"> // Can only overflow if the signed bit of the two values do not match. If the
</span><span class="cx"> // signed bit of the result and the first value differ it did overflow.
</span><del>- if ((ua ^ ub) >> 31 & (result ^ ua) >> 31)
- result = std::numeric_limits<int>::max() + (ua >> 31);
</del><ins>+ return (ua ^ ub) >> 31 & (uresult ^ ua) >> 31;
+#endif
+}
</ins><span class="cx">
</span><ins>+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<uint32_t>::max() + (static_cast<uint32_t>(a) >> 31);
+#endif
</ins><span class="cx"> return result;
</span><span class="cx"> }
</span><span class="cx">
</span></span></pre>
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