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LibCrypto: Add UnsignedBigInteger subtraction and comparison

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Itamar 2020-04-08 13:07:47 +03:00 • committed by Andreas Kling
parent 6201f741d4
commit e0cf40518c
3 changed files with 138 additions and 8 deletions
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60
Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
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@ -64,11 +64,47 @@ UnsignedBigInteger UnsignedBigInteger::add(const UnsignedBigInteger& other)
return result;
}
UnsignedBigInteger UnsignedBigInteger::sub(const UnsignedBigInteger& other)
{
UnsignedBigInteger result;
if (*this < other) {
dbg() << "WARNING: bigint subtraction creates a negative number!";
return UnsignedBigInteger::create_invalid();
}
u8 borrow = 0;
for (size_t i = 0; i < other.length(); ++i) {
ASSERT(!(borrow == 1 && m_words[i] == 0));
if (m_words[i] - borrow < other.m_words[i]) {
u64 after_borrow = static_cast<u64>(m_words[i] - borrow) + (UINT32_MAX + 1);
result.m_words.append(static_cast<u32>(after_borrow - static_cast<u64>(other.m_words[i])));
borrow = 1;
} else {
result.m_words.append(m_words[i] - borrow - other.m_words[i]);
borrow = 0;
}
}
for (size_t i = other.length(); i < length(); ++i) {
ASSERT(!(borrow == 1 && m_words[i] == 0));
result.m_words.append(m_words[i] - borrow);
borrow = 0;
}
return result;
}
bool UnsignedBigInteger::operator==(const UnsignedBigInteger& other) const
{
if (trimmed_length() != other.trimmed_length()) {
return false;
}
if (is_invalid() != other.is_invalid()) {
return false;
}
for (size_t i = 0; i < trimmed_length(); ++i) {
if (m_words[i] != other.words()[i])
return false;
@ -76,6 +112,23 @@ bool UnsignedBigInteger::operator==(const UnsignedBigInteger& other) const
return true;
}
bool UnsignedBigInteger::operator<(const UnsignedBigInteger& other) const
{
if (trimmed_length() < other.trimmed_length()) {
return true;
}
if (trimmed_length() > other.trimmed_length()) {
return false;
}
size_t length = trimmed_length();
if (length == 0) {
return false;
}
return m_words[length - 1] < other.m_words[length - 1];
}
size_t UnsignedBigInteger::trimmed_length() const
{
size_t num_leading_zeroes = 0;
@ -86,4 +139,11 @@ size_t UnsignedBigInteger::trimmed_length() const
return length() - num_leading_zeroes;
}
UnsignedBigInteger UnsignedBigInteger::create_invalid()
{
UnsignedBigInteger invalid(0);
invalid.invalidate();
return invalid;
}
}