/* operands need to have m->top+1 digits of space and satisfy 0 ≤ a ≤ m-1 */

#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
mpmodadd(mpint *b1, mpint *b2, mpint *m, mpint *sum)
{
mpint *a, *b;
mpdigit d;
int i, j;

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

sum->flags |= (a->flags | b->flags) & MPtimesafe;
mpbits(sum, Dbits*2*(m->top+1));

mpvecadd(a->p, m->top, b->p, m->top, sum->p);
mpvecsub(sum->p, m->top+1, m->p, m->top, sum->p+m->top+1);

d = sum->p[2*m->top+1];
for(i = 0, j = m->top+1; i < m->top; i++, j++)
sum->p[i] = (sum->p[i] & d) | (sum->p[j] & ~d);

sum->top = m->top;
sum->sign = 1;
mpnorm(sum);

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

void
mpmodsub(mpint *b1, mpint *b2, mpint *m, mpint *diff)
{
mpint *a, *b;
mpdigit d;
int i, j;

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

diff->flags |= (a->flags | b->flags) & MPtimesafe;
mpbits(diff, Dbits*2*(m->top+1));

a->p[m->top] = 0;
mpvecsub(a->p, m->top+1, b->p, m->top, diff->p);
mpvecadd(diff->p, m->top, m->p, m->top, diff->p+m->top+1);

d = ~diff->p[m->top];
for(i = 0, j = m->top+1; i < m->top; i++, j++)
diff->p[i] = (diff->p[i] & d) | (diff->p[j] & ~d);

diff->top = m->top;
diff->sign = 1;
mpnorm(diff);

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

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);
}