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s_logb.S revision 1.1 
      1 /*-
      2  * Copyright (c) 1990 The Regents of the University of California.
      3  * All rights reserved.
      4  *
      5  * This code is derived from software contributed to Berkeley by
      6  * the Systems Programming Group of the University of Utah Computer
      7  * Science Department.
      8  *
      9  * Redistribution and use in source and binary forms, with or without
     10  * modification, are permitted provided that the following conditions
     11  * are met:
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  * 2. Redistributions in binary form must reproduce the above copyright
     15  *    notice, this list of conditions and the following disclaimer in the
     16  *    documentation and/or other materials provided with the distribution.
     17  * 3. All advertising materials mentioning features or use of this software
     18  *    must display the following acknowledgement:
     19  *	This product includes software developed by the University of
     20  *	California, Berkeley and its contributors.
     21  * 4. Neither the name of the University nor the names of its contributors
     22  *    may be used to endorse or promote products derived from this software
     23  *    without specific prior written permission.
     24  *
     25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     35  * SUCH DAMAGE.
     36  */
     37 
     38 #include <machine/asm.h>
     39 
     40 ;_sccsid:
     41 ;.asciz	"from: @(#)support.s	5.2 (Berkeley) 5/17/90"
     42 _rcsid:
     43 .asciz	"$Id: s_logb.S,v 1.1 1994/02/14 21:55:25 jtc Exp $"
     44 
     45 
     46 | logb(x)
     47 | returns the unbiased exponent of x, a signed integer in double precision,
     48 | except that logb(0) is -INF, logb(INF) is +INF, and logb(NAN) is that NAN.
     49 ENTRY(logb)
     50 	movw	sp@(4),d0
     51 	movw	#0x7FF0,d1	| exponent bits
     52 	andw	d1,d0		| mask off all else
     53 	cmpw	d1,d0		| max exponent?
     54 	bne	Lfinite		| no, is finite
     55 	fmoved	sp@(4),fp0	| yes, infinite or NaN
     56 	fbun	Ldone		| NaN returns NaN
     57 	fabsx	fp0		| +-inf returns inf
     58 	jra	Ldone
     59 Lfinite:
     60 	fmoved	sp@(4),fp0	| get entire number
     61 	fbne	Lnonz		| zero?
     62 	flog2x	fp0		| yes, log(0) a convenient source of -inf
     63 	jra	Ldone
     64 Lnonz:
     65 	fgetexpx	fp0	| get exponent
     66 	jra	Ldone
     67