ldexp.s

早期freebsd实现

/*
 * Copyright (c) 1983, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * 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(LIBC_SCCS) && !defined(lint)
	.asciz "@(#)ldexp.s	8.1 (Berkeley) 6/4/93"
#endif /* LIBC_SCCS and not lint */

/*
 * double ldexp (value, exp)
 * double value;
 * int exp;
 *
 * Ldexp returns value*2**exp, if that result is in range.
 * If underflow occurs, it returns zero.  If overflow occurs,
 * it returns a value of appropriate sign and largest
 * possible magnitude.  In case of either overflow or underflow,
 * errno is set to ERANGE.  Note that errno is not modified if
 * no error occurs.
 */

#include "DEFS.h"

/*
 * don't include errno.h, ANSI C says it defines errno.
 *
 * #include <errno.h>
 */
#define	ERANGE	34

	.globl	_errno

ENTRY(ldexp, 0)
	movd	4(ap),r0	/* fetch "value" */
	extzv	$7,$8,r0,r2	/* r2 := biased exponent */
	jeql	1f		/* if zero, done */

	addl2	12(ap),r2	/* r2 := new biased exponent */
	jleq	2f		/* if <= 0, underflow */
	cmpl	r2,$256		/* otherwise check if too big */
	jgeq	3f		/* jump if overflow */
	insv	r2,$7,$8,r0	/* put exponent back in result */
1:
	ret
2:
	clrd	r0
	jbr	1f
3:
	movd	huge,r0		/* largest possible floating magnitude */
	jbc	$15,4(ap),1f	/* jump if argument was positive */
	mnegd	r0,r0		/* if arg < 0, make result negative */
1:
	movl	$ERANGE,_errno
	ret

	.data
huge:	.word	0x7fff		/* the largest number that can */
	.word	0xffff		/*   be represented in a long floating */
	.word	0xffff		/*   number.  This is given in hex in order */
	.word	0xffff		/*   to avoid floating conversions */