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// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_DIY_FP_H_
#define V8_DIY_FP_H_
#include <stdint.h>
#include "src/base/logging.h"
namespace v8 {
namespace internal {
// 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 are not designed to contain special doubles (NaN and Infinity).
class DiyFp {
public:
static const int kSignificandSize = 64;
DiyFp() : f_(0), e_(0) {}
DiyFp(uint64_t f, int e) : f_(f), e_(e) {}
// this = this - other.
// The exponents of both numbers must be the same and the significand of this
// must be bigger than the significand of other.
// The result will not be normalized.
void Subtract(const DiyFp& other) {
DCHECK(e_ == other.e_);
DCHECK(f_ >= other.f_);
f_ -= other.f_;
}
// Returns a - b.
// The exponents of both numbers must be the same and this must be bigger
// than other. The result will not be normalized.
static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
DiyFp result = a;
result.Subtract(b);
return result;
}
// this = this * other.
void Multiply(const DiyFp& other);
// returns a * b;
static DiyFp Times(const DiyFp& a, const DiyFp& b) {
DiyFp result = a;
result.Multiply(b);
return result;
}
void Normalize() {
DCHECK(f_ != 0);
uint64_t f = f_;
int e = e_;
// This method is mainly called for normalizing boundaries. In general
// boundaries need to be shifted by 10 bits. We thus optimize for this case.
const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54;
while ((f & k10MSBits) == 0) {
f <<= 10;
e -= 10;
}
while ((f & kUint64MSB) == 0) {
f <<= 1;
e--;
}
f_ = f;
e_ = e;
}
static DiyFp Normalize(const DiyFp& a) {
DiyFp result = a;
result.Normalize();
return result;
}
uint64_t f() const { return f_; }
int e() const { return e_; }
void set_f(uint64_t new_value) { f_ = new_value; }
void set_e(int new_value) { e_ = new_value; }
private:
static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;
uint64_t f_;
int e_;
};
} // namespace internal
} // namespace v8
#endif // V8_DIY_FP_H_
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