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80 lines
2.6 KiB
C++
80 lines
2.6 KiB
C++
/*
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* Copyright (c) 2023, Dan Klishch <danilklishch@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Diagnostics.h>
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#include <AK/UFixedBigInt.h>
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namespace AK::Detail {
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template<size_t dividend_bit_size, size_t divisor_bit_size, bool restore_remainder>
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constexpr void div_mod_internal(
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StaticStorage<false, dividend_bit_size> const& operand1,
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StaticStorage<false, divisor_bit_size> const& operand2,
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StaticStorage<false, dividend_bit_size>& quotient,
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StaticStorage<false, divisor_bit_size>& remainder)
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{
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using Ops = StorageOperations<>;
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size_t dividend_len = operand1.size(), divisor_len = operand2.size();
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while (divisor_len > 0 && !operand2[divisor_len - 1])
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--divisor_len;
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while (dividend_len > 0 && !operand1[dividend_len - 1])
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--dividend_len;
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// FIXME: Should raise SIGFPE instead
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VERIFY(divisor_len); // VERIFY(divisor != 0)
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// Fast paths
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if (divisor_len == 1 && operand2[0] == 1) { // divisor == 1
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quotient = operand1;
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if constexpr (restore_remainder)
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Ops::set(0, remainder);
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return;
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}
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if (dividend_len < divisor_len) { // dividend < divisor
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Ops::set(0, quotient);
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if constexpr (restore_remainder)
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Ops::copy(operand1, remainder);
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return;
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}
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if (divisor_len == 1 && dividend_len == 1) { // NativeWord / NativeWord
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Ops::set(operand1[0] / operand2[0], quotient);
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if constexpr (restore_remainder)
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Ops::set(operand1[0] % operand2[0], remainder);
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return;
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}
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if (divisor_len == 1) { // BigInt by NativeWord
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auto u = (static_cast<NativeDoubleWord>(operand1[dividend_len - 1]) << native_word_size) + operand1[dividend_len - 2];
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auto divisor = operand2[0];
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auto top = u / divisor;
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quotient[dividend_len - 1] = static_cast<NativeWord>(top >> native_word_size);
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quotient[dividend_len - 2] = static_cast<NativeWord>(top);
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auto carry = static_cast<NativeWord>(u % divisor);
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for (size_t i = dividend_len - 2; i--;)
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quotient[i] = div_mod_words(operand1[i], carry, divisor, carry);
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for (size_t i = dividend_len; i < quotient.size(); ++i)
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quotient[i] = 0;
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if constexpr (restore_remainder)
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Ops::set(carry, remainder);
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return;
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}
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// Knuth's algorithm D
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StaticStorage<false, dividend_bit_size + native_word_size> dividend;
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Ops::copy(operand1, dividend);
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auto divisor = operand2;
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Ops::div_mod_internal<restore_remainder>(dividend, divisor, quotient, remainder, dividend_len, divisor_len);
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}
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}
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