diff options
Diffstat (limited to 'mfbt/double-conversion/diy-fp.cc')
| -rw-r--r-- | mfbt/double-conversion/diy-fp.cc | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/mfbt/double-conversion/diy-fp.cc b/mfbt/double-conversion/diy-fp.cc new file mode 100644 index 000000000..ddd1891b1 --- /dev/null +++ b/mfbt/double-conversion/diy-fp.cc @@ -0,0 +1,57 @@ +// Copyright 2010 the V8 project authors. All rights reserved. +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions are +// met: +// +// * Redistributions of source code must retain the above copyright +// notice, this list of conditions and the following disclaimer. +// * Redistributions in binary form must reproduce the above +// copyright notice, this list of conditions and the following +// disclaimer in the documentation and/or other materials provided +// with the distribution. +// * Neither the name of Google Inc. nor the names of its +// contributors may be used to endorse or promote products derived +// from this software without specific prior written permission. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + + +#include "diy-fp.h" +#include "utils.h" + +namespace double_conversion { + +void DiyFp::Multiply(const DiyFp& other) { + // Simply "emulates" a 128 bit multiplication. + // However: the resulting number only contains 64 bits. The least + // significant 64 bits are only used for rounding the most significant 64 + // bits. + const uint64_t kM32 = 0xFFFFFFFFU; + uint64_t a = f_ >> 32; + uint64_t b = f_ & kM32; + uint64_t c = other.f_ >> 32; + uint64_t d = other.f_ & kM32; + uint64_t ac = a * c; + uint64_t bc = b * c; + uint64_t ad = a * d; + uint64_t bd = b * d; + uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); + // By adding 1U << 31 to tmp we round the final result. + // Halfway cases will be round up. + tmp += 1U << 31; + uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); + e_ += other.e_ + 64; + f_ = result_f; +} + +} // namespace double_conversion |