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 //
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7 // notice, this list of conditions and the following disclaimer.
8 // * Redistributions in binary form must reproduce the above
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15 //
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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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
Multiply(const DiyFp & other)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
59