First Commit

For Azeroth!

dep/g3dlite/source/uint128.cpp

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+/**
+ @file uint128.cpp
+ 
+ @maintainer Morgan McGuire, http://graphics.cs.williams.edu
+ @author Kyle Whitson
+ 
+ @created 2008-07-17
+ @edited  2008-07-17
+ */
+
+#include "G3D/uint128.h"
+
+namespace G3D {
+
+/** Adds two 64-bit integers, placing the result and the overflow into 64-bit integers.*/
+static void addAndCarry(const uint64& _a, const uint64& _b, uint64& carry, uint64& result) {
+        
+    // Break each number into 4 32-bit chunks. Since we are using uints, right-shifting will fill with zeros.
+    // This eliminates the need to and with 0xFFFFFFFF.
+    uint32 a [2] = {_a & 0xFFFFFFFF, _a >> 32};
+    uint32 b [2] = {_b & 0xFFFFFFFF, _b >> 32};
+
+    uint64 tmp = uint64(a[0]) + b[0];
+
+    result = tmp & 0xFFFFFFFF;
+    uint32 c = tmp >> 32;
+
+    tmp = uint64(c) + a[1] + b[1];
+    result += tmp << 32;
+    carry = (tmp >> 32);
+}
+
+/** Multiplies two unsigned 64-bit integers, placing the result into one 64-bit int and the overflow into another.*/
+void multiplyAndCarry(const uint64& _a, const uint64& _b, uint64& carry, uint64& result) {
+
+    // Break each number into 4 32-bit chunks. Since we are using uints, right-shifting will fill with zeros.
+    // This eliminates the need to and with 0xFFFFFFFF.
+    uint32 a [2] = {_a & 0xFFFFFFFF, _a >> 32};
+    uint32 b [2] = {_b & 0xFFFFFFFF, _b >> 32};
+
+    uint64 prod [2][2];
+    for(int i = 0; i < 2; ++i) {
+        for(int j = 0; j < 2; ++j) {
+            prod[i][j] = uint64(a[i]) * b[j];
+        }
+    }
+
+    // The product of the low bits of a and b will always fit into the result
+    result = prod[0][0];
+
+    // The product of the high bits of a and b will never fit into the result
+    carry = prod[1][1];
+
+    // The high 32 bits of prod[0][1] and prod[1][0] will never fit into the result
+    carry += prod[0][1] >> 32;
+    carry += prod[1][0] >> 32;
+
+    uint64 tmp;
+    addAndCarry(result, (prod[0][1] << 32), tmp, result);
+    carry += tmp;
+    addAndCarry(result, (prod[1][0] << 32), tmp, result);
+    carry += tmp;
+}
+
+
+uint128::uint128(const uint64& hi, const uint64& lo) : hi(hi), lo(lo) {
+}
+
+uint128::uint128(const uint64& lo) : hi(0), lo(lo) {
+}
+
+uint128& uint128::operator+=(const uint128& x) {
+
+    G3D::uint64 carry;
+    addAndCarry(lo, x.lo, carry, lo);
+
+    // Adding the carry will change hi. Save the old hi bits in case this == x.
+    const uint64 xHi = x.hi;
+    hi += carry;
+    hi += xHi;
+    return *this;
+}
+
+uint128& uint128::operator*=(const uint128& x) {
+
+    // The low bits will get overwritten when doing the multiply, so back up both (in case &x == this)
+    const uint64 oldLo = lo;
+    const uint64 oldXLo = x.lo;
+
+    G3D::uint64 carry;
+    multiplyAndCarry(oldLo, oldXLo, carry, lo);
+
+    // Overflow doesn't matter here because the result is going into hi - any overflow will exceed the capacity of a 128-bit number
+    // Note: hi * x.hi will always overflow, since (x * 2^64) * (y * 2^64) = x*y*(2^128). The largest number expressable in 128 bits is
+    // 2^128 - 1.
+    hi = carry + (oldLo * x.hi) + (hi * oldXLo);
+
+    return *this;
+}
+
+uint128& uint128::operator^=(const uint128& x) {
+    hi ^= x.hi;
+    lo ^= x.lo;
+    return *this;
+}
+
+uint128& uint128::operator&=(const uint128& x) {
+    hi &= x.hi;
+    lo &= x.lo;
+    return *this;
+}
+
+uint128& uint128::operator|=(const uint128& x) {
+    hi |= x.hi;
+    lo |= x.lo;
+    return *this;
+}
+
+bool uint128::operator==(const uint128& x) {
+    return (hi == x.hi) && (lo == x.lo);
+}
+
+uint128& uint128::operator>>=(const int x) {
+
+    //Before shifting, mask out the bits that will be shifted out of hi.
+    //Put a 1 in the first bit that will not be lost in the shift, then subtract 1 to get the mask.
+    uint64 mask = ((uint64)1L << x) - 1;
+    uint64 tmp = hi & mask;
+    hi >>= x;
+
+    //Shift lo and add the bits shifted down from hi
+    lo = (lo >> x) + (tmp << (64 - x));
+    
+    return *this;
+}
+
+uint128& uint128::operator<<=(const int x) {
+
+    //Before shifting, mask out the bits that will be shifted out of lo.
+    //Put a 1 in the last bit that will be lost in the shift, then subtract 1 to get the logical inverse of the mask.
+    //A bitwise NOT will then produce the correct mask.
+    uint64 mask = ~((((uint64)1L) << (64 - x)) - 1);
+    uint64 tmp = lo & mask;
+    lo <<= x;
+
+    //Shift hi and add the bits shifted up from lo
+    hi = (hi << x) + (tmp >> (64 - x));
+    
+    return *this;
+}
+
+uint128 uint128::operator&(const uint128& x) {
+    return uint128(hi & x.hi, lo & x.lo);
+}
+}