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