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UnsignedBigInteger stores an unsigned ainteger of arbitrary length. A big integer is represented as a vector of word. Each word is an unsigned int.
90 lines
3.1 KiB
C++
90 lines
3.1 KiB
C++
/*
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* Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "UnsignedBigInteger.h"
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namespace Crypto {
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UnsignedBigInteger UnsignedBigInteger::add(const UnsignedBigInteger& other)
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{
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const UnsignedBigInteger* const longer = (length() > other.length()) ? this : &other;
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const UnsignedBigInteger* const shorter = (longer == &other) ? this : &other;
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UnsignedBigInteger result;
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u8 carry = 0;
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for (size_t i = 0; i < shorter->length(); ++i) {
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u32 word_addition_result = shorter->m_words[i] + longer->m_words[i];
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u8 carry_out = 0;
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// if there was a carry, the result will be smaller than any of the operands
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if (word_addition_result < shorter->m_words[i]) {
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carry_out = 1;
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}
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if (carry) {
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word_addition_result++;
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}
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carry = carry_out;
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result.m_words.append(word_addition_result);
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}
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for (size_t i = shorter->length(); i < longer->length(); ++i) {
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u32 word_addition_result = longer->m_words[i] + carry;
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carry = 0;
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if (word_addition_result < longer->m_words[i]) {
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carry = 1;
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}
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result.m_words.append(word_addition_result);
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}
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if (carry) {
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result.m_words.append(carry);
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}
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return result;
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}
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bool UnsignedBigInteger::operator==(const UnsignedBigInteger& other) const
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{
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if (trimmed_length() != other.trimmed_length()) {
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return false;
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}
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for (size_t i = 0; i < trimmed_length(); ++i) {
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if (m_words[i] != other.words()[i])
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return false;
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}
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return true;
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}
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size_t UnsignedBigInteger::trimmed_length() const
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{
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size_t num_leading_zeroes = 0;
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for (int i = length() - 1; i >= 0; --i, ++num_leading_zeroes) {
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if (m_words[i] != 0)
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break;
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}
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return length() - num_leading_zeroes;
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}
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}
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