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AK: Implement Knuth's algorithm D for dividing UFixedBigInt's

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Dan Klishch 2023-02-04 18:57:10 +03:00 • committed by Andrew Kaster
parent 2470fab05e
commit 2d27c98659
4 changed files with 233 additions and 67 deletions
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106
AK/UFixedBigInt.h
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@ -60,6 +60,13 @@ constexpr void mul_internal(Operand1 const& operand1, Operand2 const& operand2,
StorageOperations::baseline_mul(operand1, operand2, result, g_null_allocator);
}
template<size_t dividend_size, size_t divisor_size, bool restore_remainder>
constexpr void div_mod_internal( // Include AK/UFixedBigIntDivision.h to use UFixedBigInt division
StaticStorage<false, dividend_size> const& dividend,
StaticStorage<false, divisor_size> const& divisor,
StaticStorage<false, dividend_size>& quotient,
StaticStorage<false, divisor_size>& remainder);
template<size_t bit_size, typename Storage>
class UFixedBigInt {
constexpr static size_t static_size = Storage::static_size;
@ -395,84 +402,49 @@ public:
return result;
}
// FIXME: Refactor out this
using R = UFixedBigInt<bit_size>;
static constexpr size_t my_size()
template<NotBuiltInUFixedInt T>
constexpr UFixedBigInt<bit_size> div_mod(T const& divisor, T& remainder) const
{
return sizeof(Storage);
}
// FIXME: Do something smarter (process at least one word per iteration).
// FIXME: no restraints on this
template<Unsigned U>
requires(sizeof(Storage) >= sizeof(U)) constexpr R div_mod(U const& divisor, U& remainder) const
{
// FIXME: Is there a better way to raise a division by 0?
// Maybe as a compiletime warning?
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdiv-by-zero"
if (!divisor) {
int volatile x = 1;
int volatile y = 0;
[[maybe_unused]] int volatile z = x / y;
}
#pragma GCC diagnostic pop
// fastpaths
if (*this < divisor) {
remainder = static_cast<U>(*this);
return 0u;
}
if (*this == divisor) {
remainder = 0u;
return 1u;
}
if (divisor == 1u) {
remainder = 0u;
return *this;
}
remainder = 0u;
R quotient = 0u;
for (ssize_t i = sizeof(R) * 8 - clz() - 1; i >= 0; --i) {
remainder <<= 1u;
remainder |= static_cast<unsigned>(*this >> (size_t)i) & 1u;
if (remainder >= divisor) {
remainder -= divisor;
quotient |= R { 1u } << (size_t)i;
}
}
UFixedBigInt<bit_size> quotient;
UFixedBigInt<assumed_bit_size<T>> resulting_remainder;
div_mod_internal<bit_size, assumed_bit_size<T>, true>(m_data, get_storage_of(divisor), get_storage_of(quotient), get_storage_of(resulting_remainder));
remainder = resulting_remainder;
return quotient;
}
template<Unsigned U>
constexpr R operator/(U const& other) const
template<UFixedInt T>
constexpr auto operator/(T const& other) const
{
U mod { 0u }; // unused
return div_mod(other, mod);
}
template<Unsigned U>
constexpr U operator%(U const& other) const
{
R res { 0u };
div_mod(other, res);
return res;
UFixedBigInt<bit_size> quotient;
StaticStorage<false, assumed_bit_size<T>> remainder; // unused
div_mod_internal<bit_size, assumed_bit_size<T>, false>(m_data, get_storage_of(other), get_storage_of(quotient), remainder);
return quotient;
}
template<Unsigned U>
constexpr R& operator/=(U const& other)
template<UFixedInt T>
constexpr auto operator%(T const& other) const
{
*this = *this / other;
return *this;
StaticStorage<false, bit_size> quotient; // unused
UFixedBigInt<assumed_bit_size<T>> remainder;
div_mod_internal<bit_size, assumed_bit_size<T>, true>(m_data, get_storage_of(other), quotient, get_storage_of(remainder));
return remainder;
}
constexpr auto operator/(IntegerWrapper const& other) const { return *this / static_cast<UFixedBigInt<32>>(other); }
constexpr auto operator%(IntegerWrapper const& other) const { return *this % static_cast<UFixedBigInt<32>>(other); }
template<UFixedInt T>
constexpr auto& operator/=(T const& other) { return *this = *this / other; }
constexpr auto& operator/=(IntegerWrapper const& other) { return *this = *this / other; }
template<Unsigned U>
constexpr R& operator%=(U const& other)
constexpr auto& operator%=(U const& other) { return *this = *this % other; }
constexpr auto& operator%=(IntegerWrapper const& other) { return *this = *this % other; }
// FIXME: Replace uses with more general `assumed_bit_size<T>`.
static constexpr size_t my_size()
{
*this = *this % other;
return *this;
return sizeof(Storage);
}
// Note: If there ever be need for non side-channel proof sqrt/pow/pow_mod of UFixedBigInt, you