ref: f0ea8a3f6019b4fe7d37f33b0a5a3a88fd1fcdc7
dir: /sys/src/cmd/unix/drawterm/libmp/mpmod.c/
#include "os.h"
#include <mp.h>
#include "dat.h"
// remainder = b mod m
//
// knuth, vol 2, pp 398-400
void
mpmod(mpint *b, mpint *m, mpint *remainder)
{
mpdiv(b, m, nil, remainder);
if(remainder->sign < 0)
mpadd(m, remainder, remainder);
}