#include "os.h"
#include <mp.h>

/* operands need to have m->top+1 digits of space and satisfy 0 ≤ a ≤ m-1 */
static mpint*
modarg(mpint *a, mpint *m)
{
	if(a->size <= m->top || a->sign < 0 || mpmagcmp(a, m) >= 0){
		a = mpcopy(a);
		mpmod(a, m, a);
		mpbits(a, Dbits*(m->top+1));
		a->top = m->top;
	} else if(a->top < m->top){
		memset(&a->p[a->top], 0, (m->top - a->top)*Dbytes);
	}
	return a;
}

void
mpmodmul(mpint *b1, mpint *b2, mpint *m, mpint *prod)
{
	mpint *a, *b;

	a = modarg(b1, m);
	b = modarg(b2, m);

	mpmul(a, b, prod);
	mpmod(prod, m, prod);

	if(a != b1)
		mpfree(a);
	if(b != b2)
		mpfree(b);
}