--- /dev/null
+/*
+ * Copyright (C) 2011 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 APPLE INC. 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 Uint16WithFraction_h
+#define Uint16WithFraction_h
+
+#include <wtf/MathExtras.h>
+
+namespace JSC {
+
+// Would be nice if this was a static const member, but the OS X linker
+// seems to want a symbol in the binary in that case...
+#define oneGreaterThanMaxUInt16 0x10000
+
+// A uint16_t with an infinite precision fraction. Upon overflowing
+// the uint16_t range, this class will clamp to oneGreaterThanMaxUInt16.
+// This is used in converting the fraction part of a number to a string.
+class Uint16WithFraction {
+public:
+ explicit Uint16WithFraction(double number, uint16_t divideByExponent = 0)
+ {
+ ASSERT(number && isfinite(number) && !signbit(number));
+
+ // Check for values out of uint16_t range.
+ if (number >= oneGreaterThanMaxUInt16) {
+ m_values.append(oneGreaterThanMaxUInt16);
+ m_leadingZeros = 0;
+ return;
+ }
+
+ // Append the units to m_values.
+ double integerPart = floor(number);
+ m_values.append(static_cast<uint32_t>(integerPart));
+
+ bool sign;
+ int32_t exponent;
+ uint64_t mantissa;
+ decomposeDouble(number - integerPart, sign, exponent, mantissa);
+ ASSERT(!sign && exponent < 0);
+ exponent -= divideByExponent;
+
+ int32_t zeroBits = -exponent;
+ --zeroBits;
+
+ // Append the append words for to m_values.
+ while (zeroBits >= 32) {
+ m_values.append(0);
+ zeroBits -= 32;
+ }
+
+ // Left align the 53 bits of the mantissa within 96 bits.
+ uint32_t values[3];
+ values[0] = static_cast<uint32_t>(mantissa >> 21);
+ values[1] = static_cast<uint32_t>(mantissa << 11);
+ values[2] = 0;
+ // Shift based on the remainder of the exponent.
+ if (zeroBits) {
+ values[2] = values[1] << (32 - zeroBits);
+ values[1] = (values[1] >> zeroBits) | (values[0] << (32 - zeroBits));
+ values[0] = (values[0] >> zeroBits);
+ }
+ m_values.append(values[0]);
+ m_values.append(values[1]);
+ m_values.append(values[2]);
+
+ // Canonicalize; remove any trailing zeros.
+ while (m_values.size() > 1 && !m_values.last())
+ m_values.removeLast();
+
+ // Count the number of leading zero, this is useful in optimizing multiplies.
+ m_leadingZeros = 0;
+ while (m_leadingZeros < m_values.size() && !m_values[m_leadingZeros])
+ ++m_leadingZeros;
+ }
+
+ Uint16WithFraction& operator*=(uint16_t multiplier)
+ {
+ ASSERT(checkConsistency());
+
+ // iteratate backwards over the fraction until we reach the leading zeros,
+ // passing the carry from one calculation into the next.
+ uint64_t accumulator = 0;
+ for (size_t i = m_values.size(); i > m_leadingZeros; ) {
+ --i;
+ accumulator += static_cast<uint64_t>(m_values[i]) * static_cast<uint64_t>(multiplier);
+ m_values[i] = static_cast<uint32_t>(accumulator);
+ accumulator >>= 32;
+ }
+
+ if (!m_leadingZeros) {
+ // With a multiplicand and multiplier in the uint16_t range, this cannot carry
+ // (even allowing for the infinity value).
+ ASSERT(!accumulator);
+ // Check for overflow & clamp to 'infinity'.
+ if (m_values[0] >= oneGreaterThanMaxUInt16) {
+ m_values.shrink(1);
+ m_values[0] = oneGreaterThanMaxUInt16;
+ m_leadingZeros = 0;
+ return *this;
+ }
+ } else if (accumulator) {
+ // Check for carry from the last multiply, if so overwrite last leading zero.
+ m_values[--m_leadingZeros] = static_cast<uint32_t>(accumulator);
+ // The limited range of the multiplier should mean that even if we carry into
+ // the units, we don't need to check for overflow of the uint16_t range.
+ ASSERT(m_values[0] < oneGreaterThanMaxUInt16);
+ }
+
+ // Multiplication by an even value may introduce trailing zeros; if so, clean them
+ // up. (Keeping the value in a normalized form makes some of the comparison operations
+ // more efficient).
+ while (m_values.size() > 1 && !m_values.last())
+ m_values.removeLast();
+ ASSERT(checkConsistency());
+ return *this;
+ }
+
+ bool operator<(const Uint16WithFraction& other)
+ {
+ ASSERT(checkConsistency());
+ ASSERT(other.checkConsistency());
+
+ // Iterate over the common lengths of arrays.
+ size_t minSize = std::min(m_values.size(), other.m_values.size());
+ for (size_t index = 0; index < minSize; ++index) {
+ // If we find a value that is not equal, compare and return.
+ uint32_t fromThis = m_values[index];
+ uint32_t fromOther = other.m_values[index];
+ if (fromThis != fromOther)
+ return fromThis < fromOther;
+ }
+ // If these numbers have the same lengths, they are equal,
+ // otherwise which ever number has a longer fraction in larger.
+ return other.m_values.size() > minSize;
+ }
+
+ // Return the floor (non-fractional portion) of the number, clearing this to zero,
+ // leaving the fractional part unchanged.
+ uint32_t floorAndSubtract()
+ {
+ // 'floor' is simple the integer portion of the value.
+ uint32_t floor = m_values[0];
+
+ // If floor is non-zero,
+ if (floor) {
+ m_values[0] = 0;
+ m_leadingZeros = 1;
+ while (m_leadingZeros < m_values.size() && !m_values[m_leadingZeros])
+ ++m_leadingZeros;
+ }
+
+ return floor;
+ }
+
+ // Compare this value to 0.5, returns -1 for less than, 0 for equal, 1 for greater.
+ int comparePoint5()
+ {
+ ASSERT(checkConsistency());
+ // If units != 0, this is greater than 0.5.
+ if (m_values[0])
+ return 1;
+ // If size == 1 this value is 0, hence < 0.5.
+ if (m_values.size() == 1)
+ return -1;
+ // Compare to 0.5.
+ if (m_values[1] > 0x80000000ul)
+ return 1;
+ if (m_values[1] < 0x80000000ul)
+ return -1;
+ // Check for more words - since normalized numbers have no trailing zeros, if
+ // there are more that two digits we can assume at least one more is non-zero,
+ // and hence the value is > 0.5.
+ return m_values.size() > 2 ? 1 : 0;
+ }
+
+ // Return true if the sum of this plus addend would be greater than 1.
+ bool sumGreaterThanOne(const Uint16WithFraction& addend)
+ {
+ ASSERT(checkConsistency());
+ ASSERT(addend.checkConsistency());
+
+ // First, sum the units. If the result is greater than one, return true.
+ // If equal to one, return true if either number has a fractional part.
+ uint32_t sum = m_values[0] + addend.m_values[0];
+ if (sum)
+ return sum > 1 || std::max(m_values.size(), addend.m_values.size()) > 1;
+
+ // We could still produce a result greater than zero if addition of the next
+ // word from the fraction were to carry, leaving a result > 0.
+
+ // Iterate over the common lengths of arrays.
+ size_t minSize = std::min(m_values.size(), addend.m_values.size());
+ for (size_t index = 1; index < minSize; ++index) {
+ // Sum the next word from this & the addend.
+ uint32_t fromThis = m_values[index];
+ uint32_t fromAddend = addend.m_values[index];
+ sum = fromThis + fromAddend;
+
+ // Check for overflow. If so, check whether the remaining result is non-zero,
+ // or if there are any further words in the fraction.
+ if (sum < fromThis)
+ return sum || (index + 1) < std::max(m_values.size(), addend.m_values.size());
+
+ // If the sum is uint32_t max, then we would carry a 1 if addition of the next
+ // digits in the number were to overflow.
+ if (sum != 0xFFFFFFFF)
+ return false;
+ }
+ return false;
+ }
+
+private:
+ bool checkConsistency() const
+ {
+ // All values should have at least one value.
+ return (m_values.size())
+ // The units value must be a uint16_t, or the value is the overflow value.
+ && (m_values[0] < oneGreaterThanMaxUInt16 || (m_values[0] == oneGreaterThanMaxUInt16 && m_values.size() == 1))
+ // There should be no trailing zeros (unless this value is zero!).
+ && (m_values.last() || m_values.size() == 1);
+ }
+
+ // The internal storage of the number. This vector is always at least one entry in size,
+ // with the first entry holding the portion of the number greater than zero. The first
+ // value always hold a value in the uint16_t range, or holds the value oneGreaterThanMaxUInt16 to
+ // indicate the value has overflowed to >= 0x10000. If the units value is oneGreaterThanMaxUInt16,
+ // there can be no fraction (size must be 1).
+ //
+ // Subsequent values in the array represent portions of the fractional part of this number.
+ // The total value of the number is the sum of (m_values[i] / pow(2^32, i)), for each i
+ // in the array. The vector should contain no trailing zeros, except for the value '0',
+ // represented by a vector contianing a single zero value. These constraints are checked
+ // by 'checkConsistency()', above.
+ //
+ // The inline capacity of the vector is set to be able to contain any IEEE double (1 for
+ // the units column, 32 for zeros introduced due to an exponent up to -3FE, and 2 for
+ // bits taken from the mantissa).
+ Vector<uint32_t, 36> m_values;
+
+ // Cache a count of the number of leading zeros in m_values. We can use this to optimize
+ // methods that would otherwise need visit all words in the vector, e.g. multiplication.
+ size_t m_leadingZeros;
+};
+
+}
+
+#endif
+
projects / apple / javascriptcore.git / blobdiff