third_party/WebKit/Source/wtf/SaturatedArithmetic.h

   1 /*
   2  * Copyright (c) 2012, Google Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
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   9  * notice, this list of conditions and the following disclaimer.
  10  *     * Redistributions in binary form must reproduce the above
  11  * copyright notice, this list of conditions and the following disclaimer
  12  * in the documentation and/or other materials provided with the
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  14  *     * Neither the name of Google Inc. nor the names of its
  15  * contributors may be used to endorse or promote products derived from
  16  * this software without specific prior written permission.
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  18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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  28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29  */
  30
  31 #ifndef SaturatedArithmetic_h
  32 #define SaturatedArithmetic_h
  33
  34 #include "wtf/CPU.h"
  35 #include <limits>
  36 #include <stdint.h>
  37
  38 #if CPU(ARM) && COMPILER(GCC) && __OPTIMIZE__
  39
  40 // If we're building ARM on GCC we replace the C++ versions with some
  41 // native ARM assembly for speed.
  42 #include "wtf/asm/SaturatedArithmeticARM.h"
  43
  44 #else
  45
  46 ALWAYS_INLINE int32_t saturatedAddition(int32_t a, int32_t b)
  47 {
  48     uint32_t ua = a;
  49     uint32_t ub = b;
  50     uint32_t result = ua + ub;
  51
  52     // Can only overflow if the signed bit of the two values match. If the
  53     // signed bit of the result and one of the values differ it overflowed.
  54
  55     if (~(ua ^ ub) & (result ^ ua) & (1 << 31))
  56         return std::numeric_limits<int>::max() + (ua >> 31);
  57
  58     return result;
  59 }
  60
  61 ALWAYS_INLINE int32_t saturatedSubtraction(int32_t a, int32_t b)
  62 {
  63     uint32_t ua = a;
  64     uint32_t ub = b;
  65     uint32_t result = ua - ub;
  66
  67     // Can only overflow if the signed bit of the two input values differ. If
  68     // the signed bit of the result and the first value differ it overflowed.
  69
  70     if ((ua ^ ub) & (result ^ ua) & (1 << 31))
  71         return std::numeric_limits<int>::max() + (ua >> 31);
  72
  73     return result;
  74 }
  75
  76 inline int getMaxSaturatedSetResultForTesting(int FractionalShift)
  77 {
  78     // For C version the set function maxes out to max int, this differs from
  79     // the ARM asm version, see SaturatedArithmetiARM.h for the equivalent asm
  80     // version.
  81     return std::numeric_limits<int>::max();
  82 }
  83
  84 inline int getMinSaturatedSetResultForTesting(int FractionalShift)
  85 {
  86     return std::numeric_limits<int>::min();
  87 }
  88
  89 ALWAYS_INLINE int saturatedSet(int value, int FractionalShift)
  90 {
  91     const int intMaxForLayoutUnit =
  92         std::numeric_limits<int>::max() >> FractionalShift;
  93
  94     const int intMinForLayoutUnit =
  95         std::numeric_limits<int>::min() >> FractionalShift;
  96
  97     if (value > intMaxForLayoutUnit)
  98         return std::numeric_limits<int>::max();
  99
 100     if (value < intMinForLayoutUnit)
 101         return std::numeric_limits<int>::min();
 102
 103     return value << FractionalShift;
 104 }
 105
 106
 107 ALWAYS_INLINE int saturatedSet(unsigned value, int FractionalShift)
 108 {
 109     const unsigned intMaxForLayoutUnit =
 110         std::numeric_limits<int>::max() >> FractionalShift;
 111
 112     if (value >= intMaxForLayoutUnit)
 113         return std::numeric_limits<int>::max();
 114
 115     return value << FractionalShift;
 116 }
 117
 118 #endif // CPU(ARM) && COMPILER(GCC)
 119 #endif // SaturatedArithmetic_h