sfnorm.s

早期freebsd实现

/*
 * Copyright (c) 1986, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Computer Consoles Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(SYSLIBC_SCCS) && !defined(lint)
	.asciz "@(#)sfnorm.s	8.1 (Berkeley) 6/4/93"
#endif /* SYSLIBC_SCCS and not lint */

#include <tahoemath/fp.h>
#include "DEFS.h"

XENTRY(sfnorm, R2|R3|R4|R5|R6)
	clrl	r1
	movl	r0,r4		/* copy to temporary. */
	jeql	retzero
	clrl	r3		/* r3 - pos of m.s.b */
inr00:	ffs	r4,r6
	incl	r6
	addl2	r6,r3
	shrl	r6,r4,r4
	jneq	inr00

cmpshift:
				/* compute the shift (r4). */
	subl3	r3,$HID_POS,r4
	jlss	shiftr		/* if less then zero we shift right. */
	shll	r4,r0,r0	/* else we shift left. */
	subl2	r4,r2		/* uodate exponent. */
	jleq	underflow	/* if less then 0 (biased) it is underflow. */
	jmp	combine		/* go to combine exponent and fraction. */
shiftr:
	mnegl	r4,r4
	shrl	r4,r0,r0	/* shift right. */
	addl2	r4,r2		/* update exponent */
	cmpl	r2,$256
	jgeq	overflow	/* check for overflow. */
combine:
	andl2	$CLEARHID,r0	/* clear the hidden bit. */
	shal	$EXPSHIFT,r2,r2	/* shift the exponent to its proper place. */
	orl2	r2,r0
	ret

underflow:
	callf	$4,sfpunder
	ret

overflow:
	callf 	$4,sfpover
	ret
retzero:
	clrl	r0
	ret