diy-fp.cc revision 014dc512cdd3e367bee49a713fdc5ed92584a3e5 
1// Copyright 2011 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "src/diy-fp.h"
6
7#include <stdint.h>
8
9namespace v8 {
10namespace internal {
11
12void DiyFp::Multiply(const DiyFp& other) {
13  // Simply "emulates" a 128 bit multiplication.
14  // However: the resulting number only contains 64 bits. The least
15  // significant 64 bits are only used for rounding the most significant 64
16  // bits.
17  const uint64_t kM32 = 0xFFFFFFFFu;
18  uint64_t a = f_ >> 32;
19  uint64_t b = f_ & kM32;
20  uint64_t c = other.f_ >> 32;
21  uint64_t d = other.f_ & kM32;
22  uint64_t ac = a * c;
23  uint64_t bc = b * c;
24  uint64_t ad = a * d;
25  uint64_t bd = b * d;
26  uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32);
27  // By adding 1U << 31 to tmp we round the final result.
28  // Halfway cases will be round up.
29  tmp += 1U << 31;
30  uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
31  e_ += other.e_ + 64;
32  f_ = result_f;
33}
34
35}  // namespace internal
36}  // namespace v8
37