Version 2.1.4.1...

src/double.h

-// 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 V8_DOUBLE_H_
-#define V8_DOUBLE_H_
-
-#include "diy_fp.h"
-
-namespace v8 {
-namespace internal {
-
-// We assume that doubles and uint64_t have the same endianness.
-static uint64_t double_to_uint64(double d) { return BitCast<uint64_t>(d); }
-static double uint64_to_double(uint64_t d64) { return BitCast<double>(d64); }
-
-// Helper functions for doubles.
-class Double {
- public:
-  static const uint64_t kSignMask = V8_2PART_UINT64_C(0x80000000, 00000000);
-  static const uint64_t kExponentMask = V8_2PART_UINT64_C(0x7FF00000, 00000000);
-  static const uint64_t kSignificandMask =
-      V8_2PART_UINT64_C(0x000FFFFF, FFFFFFFF);
-  static const uint64_t kHiddenBit = V8_2PART_UINT64_C(0x00100000, 00000000);
-
-  Double() : d64_(0) {}
-  explicit Double(double d) : d64_(double_to_uint64(d)) {}
-  explicit Double(uint64_t d64) : d64_(d64) {}
-
-  DiyFp AsDiyFp() const {
-    ASSERT(!IsSpecial());
-    return DiyFp(Significand(), Exponent());
-  }
-
-  // this->Significand() must not be 0.
-  DiyFp AsNormalizedDiyFp() const {
-    uint64_t f = Significand();
-    int e = Exponent();
-
-    ASSERT(f != 0);
-
-    // The current double could be a denormal.
-    while ((f & kHiddenBit) == 0) {
-      f <<= 1;
-      e--;
-    }
-    // Do the final shifts in one go. Don't forget the hidden bit (the '-1').
-    f <<= DiyFp::kSignificandSize - kSignificandSize - 1;
-    e -= DiyFp::kSignificandSize - kSignificandSize - 1;
-    return DiyFp(f, e);
-  }
-
-  // Returns the double's bit as uint64.
-  uint64_t AsUint64() const {
-    return d64_;
-  }
-
-  int Exponent() const {
-    if (IsDenormal()) return kDenormalExponent;
-
-    uint64_t d64 = AsUint64();
-    int biased_e = static_cast<int>((d64 & kExponentMask) >> kSignificandSize);
-    return biased_e - kExponentBias;
-  }
-
-  uint64_t Significand() const {
-    uint64_t d64 = AsUint64();
-    uint64_t significand = d64 & kSignificandMask;
-    if (!IsDenormal()) {
-      return significand + kHiddenBit;
-    } else {
-      return significand;
-    }
-  }
-
-  // Returns true if the double is a denormal.
-  bool IsDenormal() const {
-    uint64_t d64 = AsUint64();
-    return (d64 & kExponentMask) == 0;
-  }
-
-  // We consider denormals not to be special.
-  // Hence only Infinity and NaN are special.
-  bool IsSpecial() const {
-    uint64_t d64 = AsUint64();
-    return (d64 & kExponentMask) == kExponentMask;
-  }
-
-  bool IsNan() const {
-    uint64_t d64 = AsUint64();
-    return ((d64 & kExponentMask) == kExponentMask) &&
-        ((d64 & kSignificandMask) != 0);
-  }
-
-
-  bool IsInfinite() const {
-    uint64_t d64 = AsUint64();
-    return ((d64 & kExponentMask) == kExponentMask) &&
-        ((d64 & kSignificandMask) == 0);
-  }
-
-
-  int Sign() const {
-    uint64_t d64 = AsUint64();
-    return (d64 & kSignMask) == 0? 1: -1;
-  }
-
-
-  // Returns the two boundaries of this.
-  // The bigger boundary (m_plus) is normalized. The lower boundary has the same
-  // exponent as m_plus.
-  void NormalizedBoundaries(DiyFp* out_m_minus, DiyFp* out_m_plus) const {
-    DiyFp v = this->AsDiyFp();
-    bool significand_is_zero = (v.f() == kHiddenBit);
-    DiyFp m_plus = DiyFp::Normalize(DiyFp((v.f() << 1) + 1, v.e() - 1));
-    DiyFp m_minus;
-    if (significand_is_zero && v.e() != kDenormalExponent) {
-      // The boundary is closer. Think of v = 1000e10 and v- = 9999e9.
-      // Then the boundary (== (v - v-)/2) is not just at a distance of 1e9 but
-      // at a distance of 1e8.
-      // The only exception is for the smallest normal: the largest denormal is
-      // at the same distance as its successor.
-      // Note: denormals have the same exponent as the smallest normals.
-      m_minus = DiyFp((v.f() << 2) - 1, v.e() - 2);
-    } else {
-      m_minus = DiyFp((v.f() << 1) - 1, v.e() - 1);
-    }
-    m_minus.set_f(m_minus.f() << (m_minus.e() - m_plus.e()));
-    m_minus.set_e(m_plus.e());
-    *out_m_plus = m_plus;
-    *out_m_minus = m_minus;
-  }
-
-  double value() const { return uint64_to_double(d64_); }
-
- private:
-  static const int kSignificandSize = 52;  // Excludes the hidden bit.
-  static const int kExponentBias = 0x3FF + kSignificandSize;
-  static const int kDenormalExponent = -kExponentBias + 1;
-
-  uint64_t d64_;
-};
-
-} }  // namespace v8::internal
-
-#endif  // V8_DOUBLE_H_