source: trunk/minix/lib/ack/fphook/sub_ext.fc@ 12

/*
  (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
  See the copyright notice in the ACK home directory, in the file "Copyright".
*/

/* $Header: /cvsup/minix/src/lib/ack/fphook/sub_ext.fc,v 1.1 2005/10/10 15:27:44 beng Exp $ */

/*
        SUBTRACT 2 EXTENDED FORMAT NUMBERS
*/

#include "FP_types.h"

void
sub_ext(e1,e2)
EXTEND  *e1,*e2;
{
        if ((e2->m1 | e2->m2) == 0L) {
                return;
        }
        if ((e1->m1 | e1->m2) == 0L) {
                *e1 = *e2;
                e1->sign = e2->sign ? 0 : 1;
                return;
        }
        sft_ext(e1, e2);
        if (e1->sign != e2->sign) {
                /* e1 - e2 = e1 + (-e2) */
                if (b64_add(&e1->mantissa,&e2->mantissa)) { /* addition carry */
                        b64_rsft(&e1->mantissa);      /* shift mantissa one bit RIGHT */
                        e1->m1 |= 0x80000000L;  /* set max bit  */
                        e1->exp++;              /* increase the exponent */
                }
        }
        else if (e2->m1 > e1->m1 ||
                 (e2->m1 == e1->m1 && e2->m2 > e1->m2)) {
                /*      abs(e2) > abs(e1) */
                if (e1->m2 > e2->m2) {
                        e2->m1 -= 1;    /* carry in */
                }
                e2->m1 -= e1->m1;
                e2->m2 -= e1->m2;
                *e1 = *e2;
                e1->sign = e2->sign ? 0 : 1;
        }
        else {
                if (e2->m2 > e1->m2)
                        e1->m1 -= 1;    /* carry in */
                e1->m1 -= e2->m1;
                e1->m2 -= e2->m2;
        }
        nrm_ext(e1);
}