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
6 * met:
7 *
8 *     * Redistributions of source code must retain the above copyright
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
13 * distribution.
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.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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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
46ALWAYS_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
61ALWAYS_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
76inline 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
84inline int getMinSaturatedSetResultForTesting(int FractionalShift)
85{
86    return std::numeric_limits<int>::min();
87}
88
89ALWAYS_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
107ALWAYS_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
120