sub_ext.c

来自「操作系统源代码」· C语言 代码 · 共 54 行

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

/* $Header: sub_ext.c,v 1.6 93/01/05 12:06:40 ceriel 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);
}