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LibCrypto: Add a simple SignedBigInteger

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This patchset adds a simple SignedBigInteger that is entirely defined in
terms of UnsignedBigInteger.

It also adds a NumberTheory::Power function, which is terribly
inefficient, but since the use of exponentiation is very much
discouraged for large inputs, no particular attempts were made
to make it more performant.
This commit is contained in:
AnotherTest 2020-06-04 22:46:18 +04:30 • committed by Andreas Kling
parent b4591f0037
commit d8208fd37c
5 changed files with 661 additions and 0 deletions
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24
Libraries/LibCrypto/NumberTheory/ModularFunctions.h
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@ -161,6 +161,30 @@ static auto ModularPower(const UnsignedBigInteger& b, const UnsignedBigInteger&
return exp;
}
// Note: This function _will_ generate extremely huge numbers, and in doing so,
// it will allocate and free a lot of memory!
// Please use |ModularPower| if your use-case is modexp.
template<typename IntegerType>
static auto Power(const IntegerType& b, const IntegerType& e) -> IntegerType
{
IntegerType ep { e };
IntegerType base { b };
IntegerType exp { 1 };
while (!(ep < 1)) {
if (ep.words()[0] % 2 == 1)
exp.set_to(exp.multiplied_by(base));
// ep = ep / 2;
ep.set_to(ep.divided_by(2).quotient);
// base = base * base
base.set_to(base.multiplied_by(base));
}
return exp;
}
static void GCD_without_allocation(
const UnsignedBigInteger& a,
const UnsignedBigInteger& b,