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 #include "config.h" 29 30 #include "diy-fp.h" 31 #include "utils.h" 32 33 namespace WTF { 34 35 namespace double_conversion { 36 37 void DiyFp::Multiply(const DiyFp& other) { 38 // Simply "emulates" a 128 bit multiplication. 39 // However: the resulting number only contains 64 bits. The least 40 // significant 64 bits are only used for rounding the most significant 64 41 // bits. 42 const uint64_t kM32 = 0xFFFFFFFFU; 43 uint64_t a = f_ >> 32; 44 uint64_t b = f_ & kM32; 45 uint64_t c = other.f_ >> 32; 46 uint64_t d = other.f_ & kM32; 47 uint64_t ac = a * c; 48 uint64_t bc = b * c; 49 uint64_t ad = a * d; 50 uint64_t bd = b * d; 51 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); 52 // By adding 1U << 31 to tmp we round the final result. 53 // Halfway cases will be round up. 54 tmp += 1U << 31; 55 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); 56 e_ += other.e_ + 64; 57 f_ = result_f; 58 } 59 60 } // namespace double_conversion 61 62 } // namespace WTF 63
