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1 // Copyright 2010 the V8 project authors. All rights reserved. | |
2 // Redistribution and use in source and binary forms, with or without | |
3 // modification, are permitted provided that the following conditions are | |
4 // met: | |
5 // | |
6 // * Redistributions of source code must retain the above copyright | |
7 // notice, this list of conditions and the following disclaimer. | |
8 // * Redistributions in binary form must reproduce the above | |
9 // copyright notice, this list of conditions and the following | |
10 // disclaimer in the documentation and/or other materials provided | |
11 // with the distribution. | |
12 // * Neither the name of Google Inc. nor the names of its | |
13 // contributors may be used to endorse or promote products derived | |
14 // from this software without specific prior written permission. | |
15 // | |
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | |
19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT | |
20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | |
21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | |
22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | |
26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
27 | |
28 #include "v8.h" | |
29 | |
30 #include "diy_fp.h" | |
31 | |
32 namespace v8 { | |
33 namespace internal { | |
34 | |
35 void DiyFp::Multiply(const DiyFp& other) { | |
36 // Simply "emulates" a 128 bit multiplication. | |
37 // However: the resulting number only contains 64 bits. The least | |
38 // significant 64 bits are only used for rounding the most significant 64 | |
39 // bits. | |
40 const uint64_t kM32 = 0xFFFFFFFFu; | |
41 uint64_t a = f_ >> 32; | |
42 uint64_t b = f_ & kM32; | |
43 uint64_t c = other.f_ >> 32; | |
44 uint64_t d = other.f_ & kM32; | |
45 uint64_t ac = a * c; | |
46 uint64_t bc = b * c; | |
47 uint64_t ad = a * d; | |
48 uint64_t bd = b * d; | |
49 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); | |
50 // By adding 1U << 31 to tmp we round the final result. | |
51 // Halfway cases will be round up. | |
52 tmp += 1U << 31; | |
53 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); | |
54 e_ += other.e_ + 64; | |
55 f_ = result_f; | |
56 } | |
57 | |
58 } } // namespace v8::internal | |
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