runtime/BigInteger.h

   1 /*
   2  * Copyright (C) 2011 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef BigInteger_h
  27 #define BigInteger_h
  28
  29 #include <wtf/MathExtras.h>
  30
  31 namespace JSC {
  32
  33 // This is used in converting the integer part of a number to a string.
  34 class BigInteger {
  35 public:
  36     BigInteger(double number)
  37     {
  38         ASSERT(isfinite(number) && !signbit(number));
  39         ASSERT(number == floor(number));
  40
  41         bool sign;
  42         int32_t exponent;
  43         uint64_t mantissa;
  44         decomposeDouble(number, sign, exponent, mantissa);
  45         ASSERT(!sign && exponent >= 0);
  46
  47         int32_t zeroBits = exponent - 52;
  48
  49         if (zeroBits < 0) {
  50             mantissa >>= -zeroBits;
  51             zeroBits = 0;
  52         }
  53
  54         while (zeroBits >= 32) {
  55             m_values.append(0);
  56             zeroBits -= 32;
  57         }
  58
  59         // Left align the 53 bits of the mantissa within 96 bits.
  60         uint32_t values[3];
  61         values[0] = static_cast<uint32_t>(mantissa);
  62         values[1] = static_cast<uint32_t>(mantissa >> 32);
  63         values[2] = 0;
  64         // Shift based on the remainder of the exponent.
  65         if (zeroBits) {
  66             values[2] = values[1] >> (32 - zeroBits);
  67             values[1] = (values[1] << zeroBits) | (values[0] >> (32 - zeroBits));
  68             values[0] = (values[0] << zeroBits);
  69         }
  70         m_values.append(values[0]);
  71         m_values.append(values[1]);
  72         m_values.append(values[2]);
  73
  74         // Canonicalize; remove all trailing zeros.
  75         while (m_values.size() && !m_values.last())
  76             m_values.removeLast();
  77     }
  78
  79     uint32_t divide(uint32_t divisor)
  80     {
  81         uint32_t carry = 0;
  82
  83         for (size_t i = m_values.size(); i; ) {
  84             --i;
  85             uint64_t dividend = (static_cast<uint64_t>(carry) << 32) + static_cast<uint64_t>(m_values[i]);
  86
  87             uint64_t result = dividend / static_cast<uint64_t>(divisor);
  88             ASSERT(result == static_cast<uint32_t>(result));
  89             uint64_t remainder = dividend % static_cast<uint64_t>(divisor);
  90             ASSERT(remainder == static_cast<uint32_t>(remainder));
  91
  92             m_values[i] = static_cast<uint32_t>(result);
  93             carry = static_cast<uint32_t>(remainder);
  94         }
  95
  96         // Canonicalize; remove all trailing zeros.
  97         while (m_values.size() && !m_values.last())
  98             m_values.removeLast();
  99
 100         return carry;
 101     }
 102
 103     bool operator!() { return !m_values.size(); }
 104
 105 private:
 106     Vector<uint32_t, 36> m_values;
 107 };
 108
 109 }
 110
 111 #endif
 112