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,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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
saturatedAddition(int32_t a,int32_t b)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
saturatedSubtraction(int32_t a,int32_t b)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
getMaxSaturatedSetResultForTesting(int FractionalShift)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
getMinSaturatedSetResultForTesting(int FractionalShift)84 inline int getMinSaturatedSetResultForTesting(int FractionalShift)
85 {
86 return std::numeric_limits<int>::min();
87 }
88
saturatedSet(int value,int FractionalShift)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
saturatedSet(unsigned value,int FractionalShift)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
120