JavaScriptCore-1097.3.tar.gz

[apple/javascriptcore.git] / runtime / BigInteger.h

diff --git a/runtime/BigInteger.h b/runtime/BigInteger.h
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+/*
+ * 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 BigInteger_h
+#define BigInteger_h
+
+#include <wtf/MathExtras.h>
+
+namespace JSC {
+
+// This is used in converting the integer part of a number to a string.
+class BigInteger {
+public:
+    BigInteger(double number)
+    {
+        ASSERT(isfinite(number) && !signbit(number));
+        ASSERT(number == floor(number));
+
+        bool sign;
+        int32_t exponent;
+        uint64_t mantissa;
+        decomposeDouble(number, sign, exponent, mantissa);
+        ASSERT(!sign && exponent >= 0);
+
+        int32_t zeroBits = exponent - 52;
+
+        if (zeroBits < 0) {
+            mantissa >>= -zeroBits;
+            zeroBits = 0;
+        }
+
+        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);
+        values[1] = static_cast<uint32_t>(mantissa >> 32);
+        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 all trailing zeros.
+        while (m_values.size() && !m_values.last())
+            m_values.removeLast();
+    }
+
+    uint32_t divide(uint32_t divisor)
+    {
+        uint32_t carry = 0;
+
+        for (size_t i = m_values.size(); i; ) {
+            --i;
+            uint64_t dividend = (static_cast<uint64_t>(carry) << 32) + static_cast<uint64_t>(m_values[i]);
+
+            uint64_t result = dividend / static_cast<uint64_t>(divisor);
+            ASSERT(result == static_cast<uint32_t>(result));
+            uint64_t remainder = dividend % static_cast<uint64_t>(divisor);
+            ASSERT(remainder == static_cast<uint32_t>(remainder));
+            
+            m_values[i] = static_cast<uint32_t>(result);
+            carry = static_cast<uint32_t>(remainder);
+        }
+
+        // Canonicalize; remove all trailing zeros.
+        while (m_values.size() && !m_values.last())
+            m_values.removeLast();
+
+        return carry;
+    }
+
+    bool operator!() { return !m_values.size(); }
+
+private:
+    Vector<uint32_t, 36> m_values;
+};
+
+}
+
+#endif
+