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LibCrypto: Add UnsignedBigInteger and implement addition

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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.
This commit is contained in:
Itamar 2020-04-07 22:37:42 +03:00 • committed by Andreas Kling
parent 8c645916b4
commit 6201f741d4
4 changed files with 209 additions and 1 deletions
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89
Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp Normal file
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/*
* Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "UnsignedBigInteger.h"
namespace Crypto {
UnsignedBigInteger UnsignedBigInteger::add(const UnsignedBigInteger& other)
{
const UnsignedBigInteger* const longer = (length() > other.length()) ? this : &other;
const UnsignedBigInteger* const shorter = (longer == &other) ? this : &other;
UnsignedBigInteger result;
u8 carry = 0;
for (size_t i = 0; i < shorter->length(); ++i) {
u32 word_addition_result = shorter->m_words[i] + longer->m_words[i];
u8 carry_out = 0;
// if there was a carry, the result will be smaller than any of the operands
if (word_addition_result < shorter->m_words[i]) {
carry_out = 1;
}
if (carry) {
word_addition_result++;
}
carry = carry_out;
result.m_words.append(word_addition_result);
}
for (size_t i = shorter->length(); i < longer->length(); ++i) {
u32 word_addition_result = longer->m_words[i] + carry;
carry = 0;
if (word_addition_result < longer->m_words[i]) {
carry = 1;
}
result.m_words.append(word_addition_result);
}
if (carry) {
result.m_words.append(carry);
}
return result;
}
bool UnsignedBigInteger::operator==(const UnsignedBigInteger& other) const
{
if (trimmed_length() != other.trimmed_length()) {
return false;
}
for (size_t i = 0; i < trimmed_length(); ++i) {
if (m_words[i] != other.words()[i])
return false;
}
return true;
}
size_t UnsignedBigInteger::trimmed_length() const
{
size_t num_leading_zeroes = 0;
for (int i = length() - 1; i >= 0; --i, ++num_leading_zeroes) {
if (m_words[i] != 0)
break;
}
return length() - num_leading_zeroes;
}
}