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Return integer with zero signaling common factor rather than boost::optional<Z>.

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This commit is contained in:
Nick Thompson
2018-12-04 10:55:03 -07:00
parent cad4623876
commit 51b259da19
3 changed files with 16 additions and 18 deletions
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7
include/boost/integer/mod_inverse.hpp
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@ -8,7 +8,6 @@
#define BOOST_INTEGER_MOD_INVERSE_HPP
#include <stdexcept>
#include <boost/throw_exception.hpp>
#include <boost/optional.hpp>
#include <boost/integer/extended_euclidean.hpp>
namespace boost { namespace integer {
@ -21,7 +20,7 @@ namespace boost { namespace integer {
// Would mod_inverse be sometimes mistaken as the modular *additive* inverse?
// In any case, I think this is the best name we can get for this function without agonizing.
template<class Z>
boost::optional<Z> mod_inverse(Z a, Z modulus)
Z mod_inverse(Z a, Z modulus)
{
if (modulus < 2)
{
@ -32,12 +31,12 @@ boost::optional<Z> mod_inverse(Z a, Z modulus)
if (a == 0)
{
// a doesn't have a modular multiplicative inverse:
return boost::none;
return 0;
}
euclidean_result_t<Z> u = extended_euclidean(a, modulus);
if (u.gcd > 1)
{
return boost::none;
return 0;
}
// x might not be in the range 0 < x < m, let's fix that:
while (u.x <= 0)