Line data    Source code

       1             : // Copyright 2011 the V8 project authors. All rights reserved.
       2             : // Use of this source code is governed by a BSD-style license that can be
       3             : // found in the LICENSE file.
       4             : 
       5             : #ifndef V8_DIY_FP_H_
       6             : #define V8_DIY_FP_H_
       7             : 
       8             : #include <stdint.h>
       9             : 
      10             : #include "src/base/logging.h"
      11             : #include "src/base/macros.h"
      12             : 
      13             : namespace v8 {
      14             : namespace internal {
      15             : 
      16             : // This "Do It Yourself Floating Point" class implements a floating-point number
      17             : // with a uint64 significand and an int exponent. Normalized DiyFp numbers will
      18             : // have the most significant bit of the significand set.
      19             : // Multiplication and Subtraction do not normalize their results.
      20             : // DiyFp are not designed to contain special doubles (NaN and Infinity).
      21             : class DiyFp {
      22             :  public:
      23             :   static const int kSignificandSize = 64;
      24             : 
      25     5367141 :   DiyFp() : f_(0), e_(0) {}
      26           5 :   DiyFp(uint64_t f, int e) : f_(f), e_(e) {}
      27             : 
      28             :   // this = this - other.
      29             :   // The exponents of both numbers must be the same and the significand of this
      30             :   // must be bigger than the significand of other.
      31             :   // The result will not be normalized.
      32             :   void Subtract(const DiyFp& other) {
      33             :     DCHECK(e_ == other.e_);
      34             :     DCHECK(f_ >= other.f_);
      35     4266277 :     f_ -= other.f_;
      36             :   }
      37             : 
      38             :   // Returns a - b.
      39             :   // The exponents of both numbers must be the same and this must be bigger
      40             :   // than other. The result will not be normalized.
      41             :   static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
      42             :     DiyFp result = a;
      43             :     result.Subtract(b);
      44             :     return result;
      45             :   }
      46             : 
      47             : 
      48             :   // this = this * other.
      49             :   V8_EXPORT_PRIVATE void Multiply(const DiyFp& other);
      50             : 
      51             :   // returns a * b;
      52             :   static DiyFp Times(const DiyFp& a, const DiyFp& b) {
      53     7405107 :     DiyFp result = a;
      54     7405107 :     result.Multiply(b);
      55     7405107 :     return result;
      56             :   }
      57             : 
      58             :   void Normalize() {
      59             :     DCHECK_NE(f_, 0);
      60       91125 :     uint64_t f = f_;
      61             :     int e = e_;
      62             : 
      63             :     // This method is mainly called for normalizing boundaries. In general
      64             :     // boundaries need to be shifted by 10 bits. We thus optimize for this case.
      65             :     const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54;
      66     4416255 :     while ((f & k10MSBits) == 0) {
      67     2187892 :       f <<= 10;
      68     2187892 :       e -= 10;
      69             :     }
      70     2425939 :     while ((f & kUint64MSB) == 0) {
      71      197576 :       f <<= 1;
      72      197576 :       e--;
      73             :     }
      74       91125 :     f_ = f;
      75       91125 :     e_ = e;
      76             :   }
      77             : 
      78             :   static DiyFp Normalize(const DiyFp& a) {
      79             :     DiyFp result = a;
      80             :     result.Normalize();
      81             :     return result;
      82             :   }
      83             : 
      84             :   uint64_t f() const { return f_; }
      85             :   int e() const { return e_; }
      86             : 
      87          74 :   void set_f(uint64_t new_value) { f_ = new_value; }
      88          74 :   void set_e(int new_value) { e_ = new_value; }
      89             : 
      90             :  private:
      91             :   static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;
      92             : 
      93             :   uint64_t f_;
      94             :   int e_;
      95             : };
      96             : 
      97             : }  // namespace internal
      98             : }  // namespace v8
      99             : 
     100             : #endif  // V8_DIY_FP_H_