| 1 | // Copyright 2010 the V8 project authors. All rights reserved. |
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| 2 | // Redistribution and use in source and binary forms, with or without |
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| 3 | // modification, are permitted provided that the following conditions are |
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| 4 | // met: |
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| 5 | // |
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| 6 | // * Redistributions of source code must retain the above copyright |
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| 7 | // notice, this list of conditions and the following disclaimer. |
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| 8 | // * Redistributions in binary form must reproduce the above |
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| 9 | // copyright notice, this list of conditions and the following |
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| 10 | // disclaimer in the documentation and/or other materials provided |
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| 11 | // with the distribution. |
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| 12 | // * Neither the name of Google Inc. nor the names of its |
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| 13 | // contributors may be used to endorse or promote products derived |
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| 14 | // from this software without specific prior written permission. |
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| 15 | // |
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| 16 | // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
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| 17 | // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
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| 18 | // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
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| 19 | // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
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| 20 | // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
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| 21 | // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
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| 22 | // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
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| 23 | // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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| 24 | // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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| 25 | // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
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| 26 | // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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| 27 | |
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| 28 | |
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| 29 | #include <double-conversion/diy-fp.h> |
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| 30 | #include <double-conversion/utils.h> |
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| 31 | |
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| 32 | namespace double_conversion { |
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| 33 | |
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| 34 | void DiyFp::Multiply(const DiyFp& other) { |
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| 35 | // Simply "emulates" a 128 bit multiplication. |
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| 36 | // However: the resulting number only contains 64 bits. The least |
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| 37 | // significant 64 bits are only used for rounding the most significant 64 |
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| 38 | // bits. |
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| 39 | const uint64_t kM32 = 0xFFFFFFFFU; |
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| 40 | uint64_t a = f_ >> 32; |
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| 41 | uint64_t b = f_ & kM32; |
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| 42 | uint64_t c = other.f_ >> 32; |
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| 43 | uint64_t d = other.f_ & kM32; |
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| 44 | uint64_t ac = a * c; |
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| 45 | uint64_t bc = b * c; |
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| 46 | uint64_t ad = a * d; |
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| 47 | uint64_t bd = b * d; |
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| 48 | uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); |
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| 49 | // By adding 1U << 31 to tmp we round the final result. |
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| 50 | // Halfway cases will be round up. |
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| 51 | tmp += 1U << 31; |
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| 52 | uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); |
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| 53 | e_ += other.e_ + 64; |
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| 54 | f_ = result_f; |
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| 55 | } |
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| 56 | |
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| 57 | } // namespace double_conversion |
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| 58 | |
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