4.4BSD/usr/src/old/lisp/franz/68k/calqhat.c

/* Copyright (c) 1982, Regents, University of California */
struct vl	{ long high; long low; };
calqhat(uj,v1)
register long *uj, *v1;
{
	struct vl work1, work2;
	register handy, handy2;
	register qhat, rhat;
	char err;
	if(*v1==*uj) {
		/* set qhat to b-1
		 * rhat is easily calculated since if we substite b-1
		 * for qhat in the formula below, one gets (u[j+1] + v[1])
		 */
		 qhat = 0x3fffffff;
		 rhat = uj[1] + *v1;
	} else {
		/* work1 = u[j]b + u[j+1]; */
		handy2 = uj[1];
		handy = *uj;
		if(handy & 1) handy2 |= 0x40000000;
		if(handy & 2) handy2 |= 0x80000000;
		handy >>= 2;
		work1.low = handy2; work1.high = handy;
		qhat = ediv(&work1,*v1,&err);
		/* rhat = work1 - qhat*v[1]; */
		rhat = work1.high;
	}
again:
	/* check if v[2]*qhat > rhat*b+u[j+2] */
	emul(qhat,v1[1],0,&work1);
	/* work2 = rhat*b+u[j+2]; */
	{ handy2 = uj[2]; handy = rhat;
	if(handy & 1) handy2 |= 0x40000000;
	if(handy & 2) handy2 |= 0x80000000;
	handy >>= 2; work2.low = handy2; work2.high = handy; }
	vlsub(&work1,&work2);
	if(work1.high <= 0) return(qhat);
	qhat--; rhat += *v1;
	goto again;
}