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
29#include <double-conversion/diy-fp.h>
30#include <double-conversion/utils.h>
31
32namespace double_conversion {
33
34void DiyFp::Multiply(const DiyFp& other) {
35 // Simply "emulates" a 128 bit multiplication.
36 // However: the resulting number only contains 64 bits. The least
37 // significant 64 bits are only used for rounding the most significant 64
38 // bits.
39 const uint64_t kM32 = 0xFFFFFFFFU;
40 uint64_t a = f_ >> 32;
41 uint64_t b = f_ & kM32;
42 uint64_t c = other.f_ >> 32;
43 uint64_t d = other.f_ & kM32;
44 uint64_t ac = a * c;
45 uint64_t bc = b * c;
46 uint64_t ad = a * d;
47 uint64_t bd = b * d;
48 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32);
49 // By adding 1U << 31 to tmp we round the final result.
50 // Halfway cases will be round up.
51 tmp += 1U << 31;
52 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
53 e_ += other.e_ + 64;
54 f_ = result_f;
55}
56
57} // namespace double_conversion
58