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+// 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