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1 // Copyright 2010 the V8 project authors. All rights reserved. | 1 // Copyright 2010 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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26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | 26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
27 | 27 |
28 #include "diy-fp.h" | 28 #include "diy-fp.h" |
29 | 29 |
30 #include "utils.h" | 30 #include "utils.h" |
31 | 31 |
32 namespace WTF { | 32 namespace WTF { |
33 | 33 |
34 namespace double_conversion { | 34 namespace double_conversion { |
35 | 35 |
36 void DiyFp::Multiply(const DiyFp& other) { | 36 void DiyFp::Multiply(const DiyFp& other) { |
37 // Simply "emulates" a 128 bit multiplication. | 37 // Simply "emulates" a 128 bit multiplication. |
38 // However: the resulting number only contains 64 bits. The least | 38 // However: the resulting number only contains 64 bits. The least |
39 // significant 64 bits are only used for rounding the most significant 6
4 | 39 // significant 64 bits are only used for rounding the most significant 64 |
40 // bits. | 40 // bits. |
41 const uint64_t kM32 = 0xFFFFFFFFU; | 41 const uint64_t kM32 = 0xFFFFFFFFU; |
42 uint64_t a = f_ >> 32; | 42 uint64_t a = f_ >> 32; |
43 uint64_t b = f_ & kM32; | 43 uint64_t b = f_ & kM32; |
44 uint64_t c = other.f_ >> 32; | 44 uint64_t c = other.f_ >> 32; |
45 uint64_t d = other.f_ & kM32; | 45 uint64_t d = other.f_ & kM32; |
46 uint64_t ac = a * c; | 46 uint64_t ac = a * c; |
47 uint64_t bc = b * c; | 47 uint64_t bc = b * c; |
48 uint64_t ad = a * d; | 48 uint64_t ad = a * d; |
49 uint64_t bd = b * d; | 49 uint64_t bd = b * d; |
50 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); | 50 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); |
51 // By adding 1U << 31 to tmp we round the final result. | 51 // By adding 1U << 31 to tmp we round the final result. |
52 // Halfway cases will be round up. | 52 // Halfway cases will be round up. |
53 tmp += 1U << 31; | 53 tmp += 1U << 31; |
54 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); | 54 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); |
55 e_ += other.e_ + 64; | 55 e_ += other.e_ + 64; |
56 f_ = result_f; | 56 f_ = result_f; |
57 } | 57 } |
58 | 58 |
59 } // namespace double_conversion | 59 } // namespace double_conversion |
60 | 60 |
61 } // namespace WTF | 61 } // namespace WTF |
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