Line data    Source code

       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             : 
      29             : #include "diy-fp.h"
      30             : #include "utils.h"
      31             : 
      32             : namespace double_conversion {
      33             : 
      34          24 : void DiyFp::Multiply(const DiyFp& other) {
      35             :   // Simply "emulates" a 128 bit multiplication.
      36             :   // However: the resulting number only contains 64 bits. The least
      37             :   // significant 64 bits are only used for rounding the most significant 64
      38             :   // bits.
      39          24 :   const uint64_t kM32 = 0xFFFFFFFFU;
      40          24 :   uint64_t a = f_ >> 32;
      41          24 :   uint64_t b = f_ & kM32;
      42          24 :   uint64_t c = other.f_ >> 32;
      43          24 :   uint64_t d = other.f_ & kM32;
      44          24 :   uint64_t ac = a * c;
      45          24 :   uint64_t bc = b * c;
      46          24 :   uint64_t ad = a * d;
      47          24 :   uint64_t bd = b * d;
      48          24 :   uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32);
      49             :   // By adding 1U << 31 to tmp we round the final result.
      50             :   // Halfway cases will be round up.
      51          24 :   tmp += 1U << 31;
      52          24 :   uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
      53          24 :   e_ += other.e_ + 64;
      54          24 :   f_ = result_f;
      55          24 : }
      56             : 
      57             : }  // namespace double_conversion