xref: /src/lib/libm/arch/mc68881/s_logb.S

/*	$NetBSD: s_logb.S,v 1.5.4.1 1999/12/27 18:30:02 wrstuden Exp $	*/

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * the Systems Programming Group of the University of Utah Computer
 * Science Department.
 *
 * 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.
 */

#include <machine/asm.h>

;_sccsid:
;.asciz	"from: @(#)support.s	5.2 (Berkeley) 5/17/90"

RCSID("$NetBSD: s_logb.S,v 1.5.4.1 1999/12/27 18:30:02 wrstuden Exp $")

| logb(x)
| returns the unbiased exponent of x, a signed integer in double precision,
| except that logb(0) is -INF, logb(INF) is +INF, and logb(NAN) is that NAN.
ENTRY(logb)
	movw	%sp@(4),%d0
	movw	#0x7FF0,%d1	| exponent bits
	andw	%d1,%d0		| mask off all else
	cmpw	%d1,%d0		| max exponent?
	bne	Lfinite		| no, is finite
	fmoved	%sp@(4),%fp0	| yes, infinite or NaN
	fbun	Ldone		| NaN returns NaN
	fabsx	%fp0		| +-inf returns inf
	jra	Ldone
Lfinite:
	fmoved	%sp@(4),%fp0	| get entire number
	fbne	Lnonz		| zero?
	flog2x	%fp0		| yes, log(0) a convenient source of -inf
	jra	Ldone
Lnonz:
	fgetexpx %fp0		| get exponent
Ldone:
#ifndef __SVR4_ABI__
	fmoved	%fp0,%sp@-
	movel	%sp@+,%d0
	movel	%sp@+,%d1
#endif
	rts