Initial import

third_party/double-conversion/diy-fp.h

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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.
+
+#ifndef DOUBLE_CONVERSION_DIY_FP_H_
+#define DOUBLE_CONVERSION_DIY_FP_H_
+
+#include "third_party/double-conversion/utils.h"
+
+namespace double_conversion {
+
+// This "Do It Yourself Floating Point" class implements a floating-point number
+// with a uint64 significand and an int exponent. Normalized DiyFp numbers will
+// have the most significant bit of the significand set.
+// Multiplication and Subtraction do not normalize their results.
+// DiyFp store only non-negative numbers and are not designed to contain special
+// doubles (NaN and Infinity).
+class DiyFp {
+ public:
+  static const int kSignificandSize = 64;
+
+  DiyFp() : f_(0), e_(0) {}
+  DiyFp(const uint64_t significand, const int32_t exponent)
+      : f_(significand), e_(exponent) {}
+
+  // this -= other.
+  // The exponents of both numbers must be the same and the significand of this
+  // must be greater or equal than the significand of other.
+  // The result will not be normalized.
+  void Subtract(const DiyFp& other) {
+    DOUBLE_CONVERSION_ASSERT(e_ == other.e_);
+    DOUBLE_CONVERSION_ASSERT(f_ >= other.f_);
+    f_ -= other.f_;
+  }
+
+  // Returns a - b.
+  // The exponents of both numbers must be the same and a must be greater
+  // or equal than b. The result will not be normalized.
+  static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
+    DiyFp result = a;
+    result.Subtract(b);
+    return result;
+  }
+
+  // this *= other.
+  void 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;
+    const uint64_t a = f_ >> 32;
+    const uint64_t b = f_ & kM32;
+    const uint64_t c = other.f_ >> 32;
+    const uint64_t d = other.f_ & kM32;
+    const uint64_t ac = a * c;
+    const uint64_t bc = b * c;
+    const uint64_t ad = a * d;
+    const uint64_t bd = b * d;
+    // By adding 1U << 31 to tmp we round the final result.
+    // Halfway cases will be rounded up.
+    const uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32) + (1U << 31);
+    e_ += other.e_ + 64;
+    f_ = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
+  }
+
+  // returns a * b;
+  static DiyFp Times(const DiyFp& a, const DiyFp& b) {
+    DiyFp result = a;
+    result.Multiply(b);
+    return result;
+  }
+
+  void Normalize() {
+    DOUBLE_CONVERSION_ASSERT(f_ != 0);
+    uint64_t significand = f_;
+    int32_t exponent = e_;
+
+    // This method is mainly called for normalizing boundaries. In general,
+    // boundaries need to be shifted by 10 bits, and we optimize for this case.
+    const uint64_t k10MSBits =
+        DOUBLE_CONVERSION_UINT64_2PART_C(0xFFC00000, 00000000);
+    while ((significand & k10MSBits) == 0) {
+      significand <<= 10;
+      exponent -= 10;
+    }
+    while ((significand & kUint64MSB) == 0) {
+      significand <<= 1;
+      exponent--;
+    }
+    f_ = significand;
+    e_ = exponent;
+  }
+
+  static DiyFp Normalize(const DiyFp& a) {
+    DiyFp result = a;
+    result.Normalize();
+    return result;
+  }
+
+  uint64_t f() const { return f_; }
+  int32_t e() const { return e_; }
+
+  void set_f(uint64_t new_value) { f_ = new_value; }
+  void set_e(int32_t new_value) { e_ = new_value; }
+
+ private:
+  static const uint64_t kUint64MSB =
+      DOUBLE_CONVERSION_UINT64_2PART_C(0x80000000, 00000000);
+
+  uint64_t f_;
+  int32_t e_;
+};
+
+}  // namespace double_conversion
+
+#endif  // DOUBLE_CONVERSION_DIY_FP_H_