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 9 namespace v8 { 10 namespace internal { 11 Multiply(const DiyFp & other)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