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s_logb.S revision 1.6 
      1 /*	$NetBSD: s_logb.S,v 1.6 1999/11/10 16:45:40 thorpej Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1990 The Regents of the University of California.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * the Systems Programming Group of the University of Utah Computer
      9  * Science Department.
     10  *
     11  * Redistribution and use in source and binary forms, with or without
     12  * modification, are permitted provided that the following conditions
     13  * are met:
     14  * 1. Redistributions of source code must retain the above copyright
     15  *    notice, this list of conditions and the following disclaimer.
     16  * 2. Redistributions in binary form must reproduce the above copyright
     17  *    notice, this list of conditions and the following disclaimer in the
     18  *    documentation and/or other materials provided with the distribution.
     19  * 3. All advertising materials mentioning features or use of this software
     20  *    must display the following acknowledgement:
     21  *	This product includes software developed by the University of
     22  *	California, Berkeley and its contributors.
     23  * 4. Neither the name of the University nor the names of its contributors
     24  *    may be used to endorse or promote products derived from this software
     25  *    without specific prior written permission.
     26  *
     27  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     30  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     37  * SUCH DAMAGE.
     38  */
     39 
     40 #include <machine/asm.h>
     41 
     42 ;_sccsid:
     43 ;.asciz	"from: @(#)support.s	5.2 (Berkeley) 5/17/90"
     44 
     45 RCSID("$NetBSD: s_logb.S,v 1.6 1999/11/10 16:45:40 thorpej Exp $")
     46 
     47 | logb(x)
     48 | returns the unbiased exponent of x, a signed integer in double precision,
     49 | except that logb(0) is -INF, logb(INF) is +INF, and logb(NAN) is that NAN.
     50 ENTRY(logb)
     51 	movw	%sp@(4),%d0
     52 	movw	#0x7FF0,%d1	| exponent bits
     53 	andw	%d1,%d0		| mask off all else
     54 	cmpw	%d1,%d0		| max exponent?
     55 	bne	Lfinite		| no, is finite
     56 	fmoved	%sp@(4),%fp0	| yes, infinite or NaN
     57 	fbun	Ldone		| NaN returns NaN
     58 	fabsx	%fp0		| +-inf returns inf
     59 	jra	Ldone
     60 Lfinite:
     61 	fmoved	%sp@(4),%fp0	| get entire number
     62 	fbne	Lnonz		| zero?
     63 	flog2x	%fp0		| yes, log(0) a convenient source of -inf
     64 	jra	Ldone
     65 Lnonz:
     66 	fgetexpx %fp0		| get exponent
     67 Ldone:
     68 #ifndef __SVR4_ABI__
     69 	fmoved	%fp0,%sp@-
     70 	movel	%sp@+,%d0
     71 	movel	%sp@+,%d1
     72 #endif
     73 	rts
     74