00001 // Copyright 2010 the V8 project authors. All rights reserved. 00002 // Redistribution and use in source and binary forms, with or without 00003 // modification, are permitted provided that the following conditions are 00004 // met: 00005 // 00006 // * Redistributions of source code must retain the above copyright 00007 // notice, this list of conditions and the following disclaimer. 00008 // * Redistributions in binary form must reproduce the above 00009 // copyright notice, this list of conditions and the following 00010 // disclaimer in the documentation and/or other materials provided 00011 // with the distribution. 00012 // * Neither the name of Google Inc. nor the names of its 00013 // contributors may be used to endorse or promote products derived 00014 // from this software without specific prior written permission. 00015 // 00016 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 00017 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 00018 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 00019 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 00020 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 00021 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 00022 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 00023 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 00024 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 00025 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 00026 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 00027 00028 00029 #include "diy-fp.h" 00030 #include "utils.h" 00031 00032 namespace double_conversion { 00033 00034 void DiyFp::Multiply(const DiyFp& other) { 00035 // Simply "emulates" a 128 bit multiplication. 00036 // However: the resulting number only contains 64 bits. The least 00037 // significant 64 bits are only used for rounding the most significant 64 00038 // bits. 00039 const uint64_t kM32 = 0xFFFFFFFFU; 00040 uint64_t a = f_ >> 32; 00041 uint64_t b = f_ & kM32; 00042 uint64_t c = other.f_ >> 32; 00043 uint64_t d = other.f_ & kM32; 00044 uint64_t ac = a * c; 00045 uint64_t bc = b * c; 00046 uint64_t ad = a * d; 00047 uint64_t bd = b * d; 00048 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); 00049 // By adding 1U << 31 to tmp we round the final result. 00050 // Halfway cases will be round up. 00051 tmp += 1U << 31; 00052 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); 00053 e_ += other.e_ + 64; 00054 f_ = result_f; 00055 } 00056 00057 } // namespace double_conversion