Ben Murdoch | 3fb3ca8 | 2011-12-02 17:19:32 +0000 | [diff] [blame] | 1 | // Copyright 2011 the V8 project authors. All rights reserved. |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
Andrei Popescu | 402d937 | 2010-02-26 13:31:12 +0000 | [diff] [blame] | 4 | |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 5 | #include "src/diy-fp.h" |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 6 | |
| 7 | #include <stdint.h> |
Andrei Popescu | 402d937 | 2010-02-26 13:31:12 +0000 | [diff] [blame] | 8 | |
| 9 | namespace v8 { |
| 10 | namespace internal { |
| 11 | |
Steve Block | 6ded16b | 2010-05-10 14:33:55 +0100 | [diff] [blame] | 12 | void 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 | } |
Andrei Popescu | 402d937 | 2010-02-26 13:31:12 +0000 | [diff] [blame] | 34 | |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 35 | } // namespace internal |
| 36 | } // namespace v8 |