michael@0: // Copyright 2010 the V8 project authors. All rights reserved.
michael@0: // Redistribution and use in source and binary forms, with or without
michael@0: // modification, are permitted provided that the following conditions are
michael@0: // met:
michael@0: //
michael@0: //     * Redistributions of source code must retain the above copyright
michael@0: //       notice, this list of conditions and the following disclaimer.
michael@0: //     * Redistributions in binary form must reproduce the above
michael@0: //       copyright notice, this list of conditions and the following
michael@0: //       disclaimer in the documentation and/or other materials provided
michael@0: //       with the distribution.
michael@0: //     * Neither the name of Google Inc. nor the names of its
michael@0: //       contributors may be used to endorse or promote products derived
michael@0: //       from this software without specific prior written permission.
michael@0: //
michael@0: // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
michael@0: // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
michael@0: // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
michael@0: // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
michael@0: // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
michael@0: // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
michael@0: // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
michael@0: // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
michael@0: // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
michael@0: // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
michael@0: // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
michael@0: 
michael@0: 
michael@0: #include "diy-fp.h"
michael@0: #include "utils.h"
michael@0: 
michael@0: namespace double_conversion {
michael@0: 
michael@0: void DiyFp::Multiply(const DiyFp& other) {
michael@0:   // Simply "emulates" a 128 bit multiplication.
michael@0:   // However: the resulting number only contains 64 bits. The least
michael@0:   // significant 64 bits are only used for rounding the most significant 64
michael@0:   // bits.
michael@0:   const uint64_t kM32 = 0xFFFFFFFFU;
michael@0:   uint64_t a = f_ >> 32;
michael@0:   uint64_t b = f_ & kM32;
michael@0:   uint64_t c = other.f_ >> 32;
michael@0:   uint64_t d = other.f_ & kM32;
michael@0:   uint64_t ac = a * c;
michael@0:   uint64_t bc = b * c;
michael@0:   uint64_t ad = a * d;
michael@0:   uint64_t bd = b * d;
michael@0:   uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32);
michael@0:   // By adding 1U << 31 to tmp we round the final result.
michael@0:   // Halfway cases will be round up.
michael@0:   tmp += 1U << 31;
michael@0:   uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
michael@0:   e_ += other.e_ + 64;
michael@0:   f_ = result_f;
michael@0: }
michael@0: 
michael@0: }  // namespace double_conversion