Revert grisu commits.

src/diy_fp.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_DIY_FP_H_
-#define V8_DIY_FP_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) {
-    ASSERT(e_ == other.e_);
-    ASSERT(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) {
-    // 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;
-    uint64_t a = f_ >> 32;
-    uint64_t b = f_ & kM32;
-    uint64_t c = other.f_ >> 32;
-    uint64_t d = other.f_ & kM32;
-    uint64_t ac = a * c;
-    uint64_t bc = b * c;
-    uint64_t ad = a * d;
-    uint64_t bd = b * d;
-    uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32);
-    tmp += 1U << 31;  // round
-    uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
-    e_ += other.e_ + 64;
-    f_ = result_f;
-  }
-
-  // returns a * b;
-  static DiyFp Times(const DiyFp& a, const DiyFp& b) {
-    DiyFp result = a;
-    result.Multiply(b);
-    return result;
-  }
-
-  void Normalize() {
-    ASSERT(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 = V8_2PART_UINT64_C(0xFFC00000, 00000000);
-    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 = V8_2PART_UINT64_C(0x80000000, 00000000);
-
-  uint64_t f_;
-  int e_;
-};
-
-} }  // namespace v8::internal
-
-#endif  // V8_DIY_FP_H_