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Add multiplication and division to uint160/uint256

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This commit is contained in:
Pieter Wuille
2014-04-20 01:03:19 +02:00
parent 4d480c8a3f
commit a7031507e6
2 changed files with 141 additions and 0 deletions
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70
src/uint256.h
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@@ -222,6 +222,57 @@ public:
return *this;
}
base_uint& operator*=(uint32_t b32)
{
uint64_t carry = 0;
for (int i = 0; i < WIDTH; i++)
{
uint64_t n = carry + (uint64_t)b32 * pn[i];
pn[i] = n & 0xffffffff;
carry = n >> 32;
}
return *this;
}
base_uint& operator*=(const base_uint& b)
{
base_uint a = *this;
*this = 0;
for (int j = 0; j < WIDTH; j++) {
uint64_t carry = 0;
for (int i = 0; i + j < WIDTH; i++) {
uint64_t n = carry + pn[i + j] + (uint64_t)a.pn[j] * b.pn[i];
pn[i + j] = n & 0xffffffff;
carry = n >> 32;
}
}
return *this;
}
base_uint& operator/=(const base_uint& b)
{
base_uint div = b; // make a copy, so we can shift.
base_uint num = *this; // make a copy, so we can subtract.
*this = 0; // the quotient.
int num_bits = num.bits();
int div_bits = div.bits();
if (div_bits == 0)
throw uint_error("Division by zero");
if (div_bits > num_bits) // the result is certainly 0.
return *this;
int shift = num_bits - div_bits;
div <<= shift; // shift so that div and nun align.
while (shift >= 0) {
if (num >= div) {
num -= div;
pn[shift / 32] |= (1 << (shift & 31)); // set a bit of the result.
}
div >>= 1; // shift back.
shift--;
}
// num now contains the remainder of the division.
return *this;
}
base_uint& operator++()
{
@@ -338,11 +389,14 @@ public:
friend inline const base_uint operator+(const base_uint& a, const base_uint& b) { return base_uint(a) += b; }
friend inline const base_uint operator-(const base_uint& a, const base_uint& b) { return base_uint(a) -= b; }
friend inline const base_uint operator*(const base_uint& a, const base_uint& b) { return base_uint(a) *= b; }
friend inline const base_uint operator/(const base_uint& a, const base_uint& b) { return base_uint(a) /= b; }
friend inline const base_uint operator|(const base_uint& a, const base_uint& b) { return base_uint(a) |= b; }
friend inline const base_uint operator&(const base_uint& a, const base_uint& b) { return base_uint(a) &= b; }
friend inline const base_uint operator^(const base_uint& a, const base_uint& b) { return base_uint(a) ^= b; }
friend inline const base_uint operator>>(const base_uint& a, int shift) { return base_uint(a) >>= shift; }
friend inline const base_uint operator<<(const base_uint& a, int shift) { return base_uint(a) <<= shift; }
friend inline const base_uint operator*(const base_uint& a, uint32_t b) { return base_uint(a) *= b; }
std::string GetHex() const
{
@@ -417,6 +471,22 @@ public:
return sizeof(pn);
}
// Returns the position of the highest bit set plus one, or zero if the
// value is zero.
unsigned int bits() const
{
for (int pos = WIDTH-1; pos >= 0; pos--) {
if (pn[pos]) {
for (int bits = 31; bits > 0; bits--) {
if (pn[pos] & 1<<bits)
return 32*pos + bits + 1;
}
return 32*pos + 1;
}
}
return 0;
}
uint64_t GetLow64() const
{
assert(WIDTH >= 2);