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/*
* Arithmetic for prime fields GF(p)
*
* (C) 2007 Martin Doering, Christoph Ludwig, Falko Strenzke
*
* Distributed under the terms of the Botan license
*/
#include <botan/gfp_element.h>
#include <botan/numthry.h>
#include <botan/internal/def_powm.h>
#include <botan/internal/mp_asm.h>
#include <botan/internal/mp_asmi.h>
#include <ostream>
#include <assert.h>
namespace Botan {
GFpElement::GFpElement(const BigInt& p, const BigInt& value) :
mod_p(p),
m_value(value %p)
{
}
GFpElement& GFpElement::operator+=(const GFpElement& rhs)
{
BigInt workspace = m_value;
workspace += rhs.m_value;
if(workspace >= mod_p)
workspace -= mod_p;
m_value = workspace;
assert(m_value < mod_p);
assert(m_value >= 0);
return *this;
}
GFpElement& GFpElement::operator-=(const GFpElement& rhs)
{
BigInt workspace = m_value;
workspace -= rhs.m_value;
if(workspace.is_negative())
workspace += mod_p;
m_value = workspace;
assert(m_value < mod_p);
assert(m_value >= 0);
return *this;
}
GFpElement& GFpElement::operator*= (u32bit rhs)
{
BigInt workspace = m_value;
workspace *= rhs;
workspace %= mod_p;
m_value = workspace;
return *this;
}
GFpElement& GFpElement::operator*=(const GFpElement& rhs)
{
BigInt workspace = m_value;
workspace *= rhs.m_value;
workspace %= mod_p;
m_value = workspace;
return *this;
}
GFpElement& GFpElement::operator/=(const GFpElement& rhs)
{
GFpElement inv_rhs(rhs);
inv_rhs.inverse_in_place();
*this *= inv_rhs;
return *this;
}
bool GFpElement::is_zero()
{
return (m_value.is_zero());
// this is correct because x_bar = x * r = x = 0 for x = 0
}
GFpElement& GFpElement::inverse_in_place()
{
m_value = inverse_mod(m_value, mod_p);
return *this;
}
GFpElement& GFpElement::negate()
{
m_value = mod_p - m_value;
assert(m_value <= mod_p);
return *this;
}
void GFpElement::swap(GFpElement& other)
{
std::swap(m_value, other.m_value);
std::swap(mod_p, other.mod_p);
}
std::ostream& operator<<(std::ostream& output, const GFpElement& elem)
{
return output << '(' << elem.get_value() << "," << elem.get_p() << ')';
}
bool operator==(const GFpElement& lhs, const GFpElement& rhs)
{
return (lhs.get_p() == rhs.get_p() &&
lhs.get_value() == rhs.get_value());
}
GFpElement operator+(const GFpElement& lhs, const GFpElement& rhs)
{
// consider the case that lhs and rhs both use montgm:
// then += returns an element which uses montgm.
// thus the return value of op+ here will be an element
// using montgm in this case
// NOTE: the rhs might be transformed when using op+, the lhs never
GFpElement result(lhs);
result += rhs;
return result;
}
GFpElement operator-(const GFpElement& lhs, const GFpElement& rhs)
{
GFpElement result(lhs);
result -= rhs;
return result;
// NOTE: the rhs might be transformed when using op-, the lhs never
}
GFpElement operator-(const GFpElement& lhs)
{
return(GFpElement(lhs)).negate();
}
GFpElement operator*(const GFpElement& lhs, const GFpElement& rhs)
{
// consider the case that lhs and rhs both use montgm:
// then *= returns an element which uses montgm.
// thus the return value of op* here will be an element
// using montgm in this case
GFpElement result(lhs);
result *= rhs;
return result;
}
GFpElement operator*(const GFpElement& lhs, u32bit rhs)
{
GFpElement result(lhs);
result *= rhs;
return result;
}
GFpElement operator*(u32bit lhs, const GFpElement& rhs)
{
return rhs*lhs;
}
GFpElement operator/(const GFpElement& lhs, const GFpElement& rhs)
{
GFpElement result (lhs);
result /= rhs;
return result;
}
SecureVector<byte> FE2OSP(const GFpElement& elem)
{
return BigInt::encode_1363(elem.get_value(), elem.get_p().bytes());
}
GFpElement OS2FEP(MemoryRegion<byte> const& os, BigInt p)
{
return GFpElement(p, BigInt::decode(os.begin(), os.size()));
}
GFpElement inverse(const GFpElement& elem)
{
return GFpElement(elem).inverse_in_place();
}
}
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