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1 // Copyright 2006-2008 the V8 project authors. All rights reserved. | 1 // Copyright 2006-2008 the V8 project authors. All rights reserved. |
2 // Redistribution and use in source and binary forms, with or without | 2 // Redistribution and use in source and binary forms, with or without |
3 // modification, are permitted provided that the following conditions are | 3 // modification, are permitted provided that the following conditions are |
4 // met: | 4 // met: |
5 // | 5 // |
6 // * Redistributions of source code must retain the above copyright | 6 // * Redistributions of source code must retain the above copyright |
7 // notice, this list of conditions and the following disclaimer. | 7 // notice, this list of conditions and the following disclaimer. |
8 // * Redistributions in binary form must reproduce the above | 8 // * Redistributions in binary form must reproduce the above |
9 // copyright notice, this list of conditions and the following | 9 // copyright notice, this list of conditions and the following |
10 // disclaimer in the documentation and/or other materials provided | 10 // disclaimer in the documentation and/or other materials provided |
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34 | 34 |
35 // ---------------------------------------------------------------------------- | 35 // ---------------------------------------------------------------------------- |
36 // Extra POSIX/ANSI functions for Win32/MSVC. | 36 // Extra POSIX/ANSI functions for Win32/MSVC. |
37 | 37 |
38 #include "conversions.h" | 38 #include "conversions.h" |
39 #include "platform.h" | 39 #include "platform.h" |
40 | 40 |
41 namespace v8 { | 41 namespace v8 { |
42 namespace internal { | 42 namespace internal { |
43 | 43 |
44 // The fast double-to-int conversion routine does not guarantee | |
45 // rounding towards zero. | |
46 static inline int FastD2I(double x) { | |
47 #ifdef __USE_ISOC99 | |
48 // The ISO C99 standard defines the lrint() function which rounds a | |
49 // double to an integer according to the current rounding direction. | |
50 return lrint(x); | |
51 #else | |
52 // This is incredibly slow on Intel x86. The reason is that rounding | |
53 // towards zero is implied by the C standard. This means that the | |
54 // status register of the FPU has to be changed with the 'fldcw' | |
55 // instruction. This completely stalls the pipeline and takes many | |
56 // hundreds of clock cycles. | |
57 return static_cast<int>(x); | |
58 #endif | |
59 } | |
60 | |
61 | |
62 // The fast double-to-unsigned-int conversion routine does not guarantee | 44 // The fast double-to-unsigned-int conversion routine does not guarantee |
63 // rounding towards zero, or any reasonable value if the argument is larger | 45 // rounding towards zero, or any reasonable value if the argument is larger |
64 // than what fits in an unsigned 32-bit integer. | 46 // than what fits in an unsigned 32-bit integer. |
65 static inline unsigned int FastD2UI(double x) { | 47 static inline unsigned int FastD2UI(double x) { |
66 // There is no unsigned version of lrint, so there is no fast path | 48 // There is no unsigned version of lrint, so there is no fast path |
67 // in this function as there is in FastD2I. Using lrint doesn't work | 49 // in this function as there is in FastD2I. Using lrint doesn't work |
68 // for values of 2^31 and above. | 50 // for values of 2^31 and above. |
69 | 51 |
70 // Convert "small enough" doubles to uint32_t by fixing the 32 | 52 // Convert "small enough" doubles to uint32_t by fixing the 32 |
71 // least significant non-fractional bits in the low 32 bits of the | 53 // least significant non-fractional bits in the low 32 bits of the |
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119 if (!isfinite(x) || x == 0) return 0; | 101 if (!isfinite(x) || x == 0) return 0; |
120 if (x < 0 || x >= two32) x = modulo(x, two32); | 102 if (x < 0 || x >= two32) x = modulo(x, two32); |
121 x = (x >= 0) ? floor(x) : ceil(x) + two32; | 103 x = (x >= 0) ? floor(x) : ceil(x) + two32; |
122 return (int32_t) ((x >= two31) ? x - two32 : x); | 104 return (int32_t) ((x >= two31) ? x - two32 : x); |
123 } | 105 } |
124 | 106 |
125 | 107 |
126 } } // namespace v8::internal | 108 } } // namespace v8::internal |
127 | 109 |
128 #endif // V8_CONVERSIONS_INL_H_ | 110 #endif // V8_CONVERSIONS_INL_H_ |
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