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 // Copyright 2010 the V8 project authors. All rights reserved.
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 // 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.
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 //       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
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 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 // 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 "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_

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