The Tor Browser: mfbt/double-conversion/diy-fp.h@97036ab72558 (annotated)

mfbt/double-conversion/diy-fp.h@97036ab72558 (annotated)

mfbt/double-conversion/diy-fp.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 // 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 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 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);
   // 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 = UINT64_2PART_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 = UINT64_2PART_C(0x80000000, 00000000);
   uint64_t f_;
   int e_;
 };
 }  // namespace double_conversion
 #endif  // DOUBLE_CONVERSION_DIY_FP_H_

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