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AK: UFixedBigInt add efficient multiplication with full result

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Michiel Visser 2022-03-04 08:48:44 +01:00 • committed by Ali Mohammad Pur
parent ab86294660
commit 590dcb0581
1 changed files with 72 additions and 0 deletions
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72
AK/UFixedBigInt.h
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@ -37,6 +37,12 @@ struct NumericLimits<UFixedBigInt<T>> {
static constexpr bool is_signed() { return false; } static constexpr bool is_signed() { return false; }
}; };
template<Unsigned T>
struct UFixedBigIntMultiplicationResult {
T low;
T high;
};
template<typename T> template<typename T>
requires(sizeof(T) >= sizeof(u64) && IsUnsigned<T>) class UFixedBigInt { requires(sizeof(T) >= sizeof(u64) && IsUnsigned<T>) class UFixedBigInt {
public: public:
@ -534,6 +540,72 @@ public:
return res; return res;
} }
template<Unsigned U>
requires(IsSame<R, U>&& IsSame<T, u64>) constexpr UFixedBigIntMultiplicationResult<R> wide_multiply(U const& other) const
{
auto mult_64_to_128 = [](u64 a, u64 b) -> UFixedBigIntMultiplicationResult<u64> {
#ifdef __SIZEOF_INT128__
unsigned __int128 result = (unsigned __int128)a * b;
u64 low = result;
u64 high = result >> 64;
return { low, high };
#else
u32 a_low = a;
u32 a_high = (a >> 32);
u32 b_low = b;
u32 b_high = (b >> 32);
u64 ll_result = (u64)a_low * b_low;
u64 lh_result = (u64)a_low * b_high;
u64 hl_result = (u64)a_high * b_low;
u64 hh_result = (u64)a_high * b_high;
UFixedBigInt<u64> ll { ll_result, 0u };
UFixedBigInt<u64> lh { lh_result << 32, lh_result >> 32 };
UFixedBigInt<u64> hl { hl_result << 32, hl_result >> 32 };
UFixedBigInt<u64> hh { 0u, hh_result };
UFixedBigInt<u64> result = ll + lh + hl + hh;
return { result.low(), result.high() };
#endif
};
auto ll_result = mult_64_to_128(m_low, other.low());
auto lh_result = mult_64_to_128(m_low, other.high());
auto hl_result = mult_64_to_128(m_high, other.low());
auto hh_result = mult_64_to_128(m_high, other.high());
UFixedBigInt<R> ll { R { ll_result.low, ll_result.high }, R { 0u, 0u } };
UFixedBigInt<R> lh { R { 0u, lh_result.low }, R { lh_result.high, 0u } };
UFixedBigInt<R> hl { R { 0u, hl_result.low }, R { hl_result.high, 0u } };
UFixedBigInt<R> hh { R { 0u, 0u }, R { hh_result.low, hh_result.high } };
UFixedBigInt<R> result = ll + lh + hl + hh;
return { result.low(), result.high() };
}
template<Unsigned U>
requires(IsSame<R, U> && sizeof(T) > sizeof(u64)) constexpr UFixedBigIntMultiplicationResult<R> wide_multiply(U const& other) const
{
T left_low = m_low;
T left_high = m_high;
T right_low = other.low();
T right_high = other.high();
auto ll_result = left_low.wide_multiply(right_low);
auto lh_result = left_low.wide_multiply(right_high);
auto hl_result = left_high.wide_multiply(right_low);
auto hh_result = left_high.wide_multiply(right_high);
UFixedBigInt<R> ll { R { ll_result.low, ll_result.high }, R { 0u, 0u } };
UFixedBigInt<R> lh { R { 0u, lh_result.low }, R { lh_result.high, 0u } };
UFixedBigInt<R> hl { R { 0u, hl_result.low }, R { hl_result.high, 0u } };
UFixedBigInt<R> hh { R { 0u, 0u }, R { hh_result.low, hh_result.high } };
UFixedBigInt<R> result = ll + lh + hl + hh;
return { result.low(), result.high() };
}
template<Unsigned U> template<Unsigned U>
constexpr R operator/(const U& other) const constexpr R operator/(const U& other) const
{ {