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547 lines
20 KiB
C++
547 lines
20 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/BuiltinWrappers.h>
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#include <AK/Span.h>
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#include <AK/StdLibExtras.h>
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#include <AK/Types.h>
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namespace AK {
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namespace Detail {
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// Ideally, we want to store data in the native processor's words. However, for some algorithms,
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// particularly multiplication, we require double of the amount of the native word size.
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#if defined(__SIZEOF_INT128__) && defined(AK_ARCH_64_BIT)
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using NativeWord = u64;
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using DoubleWord = unsigned __int128;
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using SignedDoubleWord = __int128;
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#else
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using NativeWord = u32;
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using DoubleWord = u64;
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using SignedDoubleWord = i64;
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#endif
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template<bool sign>
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using ConditionallySignedDoubleWord = Conditional<sign, SignedDoubleWord, DoubleWord>;
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template<typename T>
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concept BuiltInUFixedInt = OneOf<T, bool, u8, u16, u32, u64, unsigned long, unsigned long long, DoubleWord>;
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template<typename T>
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constexpr inline size_t bit_width = sizeof(T) * 8;
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constexpr size_t word_size = bit_width<NativeWord>;
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constexpr NativeWord max_word = ~static_cast<NativeWord>(0);
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static_assert(word_size == 32 || word_size == 64);
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// Max big integer length is 256 MiB (2.1e9 bits) for 32-bit, 4 GiB (3.4e10 bits) for 64-bit.
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constexpr size_t max_big_int_length = 1 << (word_size == 32 ? 26 : 29);
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// ===== Static storage for big integers =====
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template<typename T, typename WordType = NativeWord>
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concept IntegerStorage = requires(T storage, size_t index) {
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{
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storage.is_negative()
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} -> SameAs<bool>;
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{
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storage.size()
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} -> SameAs<size_t>;
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{
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storage[index]
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} -> ConvertibleTo<WordType&>;
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{
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storage.data()
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} -> ConvertibleTo<WordType*>;
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};
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template<typename T>
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concept IntegerReadonlyStorage = IntegerStorage<T, NativeWord const>;
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struct NullAllocator {
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NativeWord* allocate(size_t) { VERIFY_NOT_REACHED(); }
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};
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template<typename Word, bool is_signed_>
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struct StorageSpan : AK::Span<Word> {
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using AK::Span<Word>::Span;
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constexpr static bool is_signed = is_signed_;
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explicit constexpr StorageSpan(AK::Span<Word> span)
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: AK::Span<Word>(span)
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{
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}
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constexpr bool is_negative() const
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{
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return is_signed && this->last() >> (word_size - 1);
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}
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};
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using UnsignedStorageSpan = StorageSpan<NativeWord, false>;
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using UnsignedStorageReadonlySpan = StorageSpan<NativeWord const, false>;
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// Sometimes we want to know the exact maximum amount of the bits required to represent the number.
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// However, the bit size only acts as a hint for wide multiply operations. For all other purposes,
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// `bit_size`-sized and `ceil(bit_size / word_size) * word_size`-sized `StaticStorage`s will act the
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// same.
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template<bool is_signed_, size_t bit_size>
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requires(bit_size <= max_big_int_length * word_size) struct StaticStorage {
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constexpr static size_t static_size = (bit_size + word_size - 1) / word_size;
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constexpr static bool is_signed = is_signed_;
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// We store integers in little-endian regardless of the host endianness. We use two's complement
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// representation of negative numbers and do not bother at all if `bit_size % word_size != 0`
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// (i. e. do not properly handle overflows).
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NativeWord m_data[static_size];
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constexpr bool is_negative() const
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{
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return is_signed_ && m_data[static_size - 1] >> (word_size - 1);
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}
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constexpr static size_t size()
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{
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return static_size;
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}
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constexpr NativeWord operator[](size_t i) const
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{
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return m_data[i];
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}
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constexpr NativeWord& operator[](size_t i)
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{
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return m_data[i];
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}
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constexpr NativeWord const* data() const
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{
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return m_data;
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}
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constexpr NativeWord* data()
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{
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return m_data;
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}
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};
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struct IntegerWrapper {
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StaticStorage<false, bit_width<int>> m_data;
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// There is no reason to ban u128{0} + 1 (although the second argument type is signed, the value
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// is known at the compile time to be non-negative). In order to do so, we provide overloads in
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// UFixedBigInt which take IntegerWrapper as an argument.
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consteval IntegerWrapper(int value)
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{
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if (value < 0)
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compiletime_fail("Requested implicit conversion of an integer to the unsigned one will underflow.");
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m_data[0] = static_cast<NativeWord>(value);
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}
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};
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constexpr inline auto get_storage_of(IntegerWrapper value) { return value.m_data; }
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template<BuiltInUFixedInt T>
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constexpr StaticStorage<false, bit_width<T>> get_storage_of(T value)
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{
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if constexpr (sizeof(T) > sizeof(NativeWord)) {
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static_assert(sizeof(T) == 2 * sizeof(NativeWord));
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return { static_cast<NativeWord>(value), static_cast<NativeWord>(value >> word_size) };
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}
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return { static_cast<NativeWord>(value) };
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}
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// ===== Utilities =====
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ALWAYS_INLINE constexpr NativeWord extend_sign(bool sign)
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{
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return sign ? max_word : 0;
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}
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// FIXME: If available, we might try to use AVX2 and AVX512.
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ALWAYS_INLINE constexpr NativeWord add_words(NativeWord word1, NativeWord word2, bool& carry)
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{
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if (!is_constant_evaluated()) {
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#if __has_builtin(__builtin_addc)
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NativeWord ncarry, output;
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if constexpr (SameAs<NativeWord, unsigned int>)
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output = __builtin_addc(word1, word2, carry, reinterpret_cast<unsigned int*>(&ncarry));
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else if constexpr (SameAs<NativeWord, unsigned long>)
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output = __builtin_addcl(word1, word2, carry, reinterpret_cast<unsigned long*>(&ncarry));
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else if constexpr (SameAs<NativeWord, unsigned long long>)
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output = __builtin_addcll(word1, word2, carry, reinterpret_cast<unsigned long long*>(&ncarry));
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else
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VERIFY_NOT_REACHED();
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carry = ncarry;
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return output;
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#elif ARCH(X86_64)
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unsigned long long output;
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carry = __builtin_ia32_addcarryx_u64(carry, word1, word2, &output);
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return static_cast<NativeWord>(output);
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#endif
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}
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// Note: This is usually too confusing for both GCC and Clang.
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NativeWord output;
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bool ncarry = __builtin_add_overflow(word1, word2, &output);
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if (carry) {
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++output;
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if (output == 0)
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ncarry = true;
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}
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carry = ncarry;
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return output;
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}
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ALWAYS_INLINE constexpr NativeWord sub_words(NativeWord word1, NativeWord word2, bool& carry)
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{
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if (!is_constant_evaluated()) {
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#if __has_builtin(__builtin_subc) && !defined(AK_BUILTIN_SUBC_BROKEN)
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NativeWord ncarry, output;
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if constexpr (SameAs<NativeWord, unsigned int>)
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output = __builtin_subc(word1, word2, carry, reinterpret_cast<unsigned int*>(&ncarry));
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else if constexpr (SameAs<NativeWord, unsigned long>)
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output = __builtin_subcl(word1, word2, carry, reinterpret_cast<unsigned long*>(&ncarry));
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else if constexpr (SameAs<NativeWord, unsigned long long>)
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output = __builtin_subcll(word1, word2, carry, reinterpret_cast<unsigned long long*>(&ncarry));
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else
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VERIFY_NOT_REACHED();
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carry = ncarry;
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return output;
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#elif ARCH(X86_64) && defined(AK_COMPILER_GCC)
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unsigned long long output;
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carry = __builtin_ia32_sbb_u64(carry, word1, word2, &output);
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return static_cast<NativeWord>(output);
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#endif
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}
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NativeWord output;
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bool ncarry = __builtin_sub_overflow(word1, word2, &output);
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if (carry) {
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if (output == 0)
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ncarry = true;
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--output;
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}
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carry = ncarry;
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return output;
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}
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// Calculate ((dividend1 << word_size) + dividend0) / divisor. Quotient should be guaranteed to fit
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// into NativeWord.
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ALWAYS_INLINE constexpr NativeWord div_mod_words(NativeWord dividend0, NativeWord dividend1, NativeWord divisor, NativeWord& remainder)
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{
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auto dividend = (static_cast<DoubleWord>(dividend1) << word_size) + dividend0;
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remainder = static_cast<NativeWord>(dividend % divisor);
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return static_cast<NativeWord>(dividend / divisor);
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}
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// ===== Operations on integer storages =====
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// Naming scheme for variables belonging to one of the operands or the result is as follows:
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// trailing digit in a name is 1 if a variable belongs to `operand1` (or the only `operand`), 2 --
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// for `operand2` and no trailing digit -- for `result`.
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struct StorageOperations {
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static constexpr void copy(IntegerReadonlyStorage auto const& operand, IntegerStorage auto&& result, size_t offset = 0)
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{
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auto fill = extend_sign(operand.is_negative());
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size_t size1 = operand.size(), size = result.size();
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for (size_t i = 0; i < size; ++i)
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result[i] = i + offset < size1 ? operand[i + offset] : fill;
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}
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static constexpr void set(NativeWord value, auto&& result)
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{
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result[0] = value;
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for (size_t i = 1; i < result.size(); ++i)
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result[i] = 0;
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}
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// `is_for_inequality' is a hint to compiler that we do not need to differentiate between < and >.
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static constexpr int compare(IntegerReadonlyStorage auto const& operand1, IntegerReadonlyStorage auto const& operand2, bool is_for_inequality)
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{
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bool sign1 = operand1.is_negative(), sign2 = operand2.is_negative();
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size_t size1 = operand1.size(), size2 = operand2.size();
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if (sign1 != sign2) {
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if (sign1)
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return -1;
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return 1;
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}
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NativeWord compare_value = extend_sign(sign1);
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bool differ_in_high_bits = false;
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if (size1 > size2) {
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for (size_t i = size1; i-- > size2;)
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if (operand1[i] != compare_value)
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differ_in_high_bits = true;
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} else if (size1 < size2) {
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for (size_t i = size2; i-- > size1;)
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if (operand2[i] != compare_value)
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differ_in_high_bits = true;
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}
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if (differ_in_high_bits)
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return (size1 > size2) ^ sign1 ? 1 : -1;
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// FIXME: Using min(size1, size2) in the next line triggers -Warray-bounds on GCC with -O2 and
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// -fsanitize=address. I have not reported this.
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// Reduced testcase: https://godbolt.org/z/TE3MbfhnE
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for (size_t i = (size1 > size2 ? size2 : size1); i--;) {
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auto word1 = operand1[i], word2 = operand2[i];
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if (is_for_inequality) {
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if (word1 != word2)
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return 1;
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} else {
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if (word1 > word2)
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return 1;
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if (word1 < word2)
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return -1;
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}
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}
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return 0;
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}
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enum class Bitwise {
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AND,
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OR,
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XOR,
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INVERT,
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};
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// Requirements:
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// - !operand1.is_signed && !operand2.is_signed && !result.is_signed (the function will also work
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// for signed storages but will extend them with zeroes regardless of the actual sign).
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template<Bitwise operation>
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static constexpr void compute_bitwise(IntegerReadonlyStorage auto const& operand1, IntegerReadonlyStorage auto const& operand2, IntegerStorage auto&& result)
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{
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size_t size1 = operand1.size(), size2 = operand2.size(), size = result.size();
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for (size_t i = 0; i < size; ++i) {
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auto word1 = i < size1 ? operand1[i] : 0;
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auto word2 = i < size2 ? operand2[i] : 0;
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if constexpr (operation == Bitwise::AND)
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result[i] = word1 & word2;
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else if constexpr (operation == Bitwise::OR)
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result[i] = word1 | word2;
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else if constexpr (operation == Bitwise::XOR)
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result[i] = word1 ^ word2;
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else if constexpr (operation == Bitwise::INVERT)
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result[i] = ~word1;
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else
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static_assert(((void)operation, false));
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}
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}
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// See `storage_compute_bitwise` for the signedness requirements.
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//
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// NOTE: We want to be able to call all of the storage_* functions like
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// `storage_*(operand1, operand2, result)`, even if some of the operands are unused (in order
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// to then easily generate most of the operators via defines). That is why we have unused
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// first operand here.
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template<Bitwise operation>
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static constexpr void compute_inplace_bitwise(IntegerReadonlyStorage auto const&, IntegerReadonlyStorage auto const& operand2, IntegerStorage auto&& result)
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{
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size_t min_size = min(result.size(), operand2.size());
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for (size_t i = 0; i < min_size; ++i) {
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if constexpr (operation == Bitwise::AND)
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result[i] &= operand2[i];
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else if constexpr (operation == Bitwise::OR)
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result[i] |= operand2[i];
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else if constexpr (operation == Bitwise::XOR)
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result[i] ^= operand2[i];
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else
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static_assert(((void)operation, false));
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}
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}
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// Requirements for the next two functions:
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// - shift < result.size() * word_size;
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// - result.size() == operand.size().
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static constexpr void shift_left(IntegerReadonlyStorage auto const& operand, size_t shift, IntegerStorage auto&& result)
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{
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size_t size = operand.size();
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size_t offset = shift / word_size, remainder = shift % word_size;
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if (shift % word_size == 0) {
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for (size_t i = size; i-- > offset;)
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result[i] = operand[i - offset];
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for (size_t i = 0; i < offset; ++i)
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result[i] = 0;
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} else {
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for (size_t i = size; --i > offset;)
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result[i] = (operand[i - offset] << remainder) | (operand[i - offset - 1] >> (word_size - remainder));
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result[offset] = operand[0] << remainder;
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for (size_t i = 0; i < offset; ++i)
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result[i] = 0;
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}
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}
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static constexpr void shift_right(IntegerReadonlyStorage auto const& operand, size_t shift, IntegerStorage auto&& result)
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{
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size_t size = operand.size();
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size_t offset = shift / word_size, remainder = shift % word_size;
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if (shift % word_size == 0) {
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for (size_t i = 0; i < size - offset; ++i)
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result[i] = operand[i + offset];
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for (size_t i = size - offset; i < size; ++i)
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result[i] = 0;
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} else {
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for (size_t i = 0; i < size - offset - 1; ++i)
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result[i] = (operand[i + offset] >> remainder) | (operand[i + offset + 1] << (word_size - remainder));
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result[size - offset - 1] = operand[size - 1] >> remainder;
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for (size_t i = size - offset; i < size; ++i)
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result[i] = 0;
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}
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}
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// Requirements:
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// - result.size() >= max(operand1.size(), operand2.size()) (not a real constraint but overflow
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// detection will not work otherwise).
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//
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// Return value:
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// Let r be the return value of the function and a, b, c -- the integer values stored in `operand1`,
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// `operand2` and `result`, respectively. Then,
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// a + b * (-1) ** subtract = c + r * 2 ** (result.size() * word_size).
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// In particular, r equals 0 iff no overflow has happened.
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template<bool subtract>
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static constexpr int add(IntegerReadonlyStorage auto const& operand1, IntegerReadonlyStorage auto const& operand2, IntegerStorage auto&& result, bool carry = false)
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{
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bool sign1 = operand1.is_negative(), sign2 = operand2.is_negative();
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auto fill1 = extend_sign(sign1), fill2 = extend_sign(sign2);
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size_t size1 = operand1.size(), size2 = operand2.size(), size = result.size();
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for (size_t i = 0; i < size; ++i) {
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auto word1 = i < size1 ? operand1[i] : fill1;
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auto word2 = i < size2 ? operand2[i] : fill2;
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if constexpr (!subtract)
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result[i] = add_words(word1, word2, carry);
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else
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result[i] = sub_words(word1, word2, carry);
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}
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if constexpr (!subtract)
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return -sign1 - sign2 + carry + result.is_negative();
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else
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return -sign1 + sign2 - carry + result.is_negative();
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}
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// See `storage_add` for the meaning of the return value.
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template<bool subtract>
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static constexpr int increment(IntegerStorage auto&& operand)
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{
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bool carry = true;
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bool sign = operand.is_negative();
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size_t size = operand.size();
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for (size_t i = 0; i < size; ++i) {
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if constexpr (!subtract)
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operand[i] = add_words(operand[i], 0, carry);
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else
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operand[i] = sub_words(operand[i], 0, carry);
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}
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if constexpr (!subtract)
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return -sign + carry + operand.is_negative();
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else
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return -sign - carry + operand.is_negative();
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}
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// Requirements:
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// - result.size() == operand.size().
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//
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// Return value: operand != 0.
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static constexpr bool negate(IntegerReadonlyStorage auto const& operand, IntegerStorage auto&& result)
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{
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bool carry = false;
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size_t size = operand.size();
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for (size_t i = 0; i < size; ++i)
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result[i] = sub_words(0, operand[i], carry);
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return carry;
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}
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// No allocations will occur if both operands are unsigned.
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template<IntegerReadonlyStorage Operand1, IntegerReadonlyStorage Operand2>
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static constexpr void baseline_mul(Operand1 const& operand1, Operand2 const& operand2, IntegerStorage auto&& __restrict__ result, auto&& buffer)
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{
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bool sign1 = operand1.is_negative(), sign2 = operand2.is_negative();
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size_t size1 = operand1.size(), size2 = operand2.size(), size = result.size();
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if (size1 == 1 && size2 == 1) {
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// We do not want to compete with the cleverness of the compiler of multiplying NativeWords.
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ConditionallySignedDoubleWord<Operand1::is_signed> word1 = operand1[0];
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ConditionallySignedDoubleWord<Operand2::is_signed> word2 = operand2[0];
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auto value = static_cast<DoubleWord>(word1 * word2);
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result[0] = value;
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if (size > 1) {
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result[1] = value >> word_size;
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auto fill = extend_sign(sign1 ^ sign2);
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for (size_t i = 2; i < result.size(); ++i)
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result[i] = fill;
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}
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return;
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}
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if (size1 < size2) {
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baseline_mul(operand2, operand1, result, buffer);
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return;
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}
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// Now size1 >= size2
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// Normalize signs
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auto data1 = operand1.data(), data2 = operand2.data();
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if (size2 < size) {
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if (sign1) {
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auto inverted = buffer.allocate(size1);
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negate(operand1, UnsignedStorageSpan { inverted, size1 });
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data1 = inverted;
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}
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if (sign2) {
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auto inverted = buffer.allocate(size2);
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negate(operand2, UnsignedStorageSpan { inverted, size2 });
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data2 = inverted;
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}
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}
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size1 = min(size1, size), size2 = min(size2, size);
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// Do schoolbook O(size1 * size2).
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DoubleWord carry = 0;
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for (size_t i = 0; i < size; ++i) {
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result[i] = static_cast<NativeWord>(carry);
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carry >>= word_size;
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size_t start_index = i >= size2 ? i - size2 + 1 : 0;
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size_t end_index = min(i + 1, size1);
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for (size_t j = start_index; j < end_index; ++j) {
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auto x = static_cast<DoubleWord>(data1[j]) * data2[i - j];
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bool ncarry = false;
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result[i] = add_words(result[i], static_cast<NativeWord>(x), ncarry);
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carry += (x >> word_size) + ncarry;
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}
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}
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if (size2 < size && (sign1 ^ sign2))
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negate(result, result);
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}
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};
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}
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using Detail::StorageOperations, Detail::NativeWord, Detail::word_size, Detail::max_word,
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Detail::UnsignedStorageSpan, Detail::UnsignedStorageReadonlySpan;
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inline Detail::NullAllocator g_null_allocator;
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}
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