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ffs.S revision 1.1 
      1 /* $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:49 christos Exp $ */
      2 
      3 /*
      4  * Copyright (c) 1995 Christopher G. Demetriou
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  * 3. All advertising materials mentioning features or use of this software
     16  *    must display the following acknowledgement:
     17  *          This product includes software developed for the
     18  *          NetBSD Project.  See http://www.NetBSD.org/ for
     19  *          information about NetBSD.
     20  * 4. The name of the author may not be used to endorse or promote products
     21  *    derived from this software without specific prior written permission.
     22  *
     23  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     24  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     25  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     26  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     27  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     28  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     29  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     30  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     31  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     32  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     33  *
     34  * <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
     35  */
     36 
     37 #include <machine/asm.h>
     38 
     39 LEAF(ffs, 1)
     40 	addl	a0, 0, t0
     41 	beq	t0, Lallzero
     42 
     43 	/*
     44 	 * Initialize return value (v0), and set up t1 so that it
     45 	 * contains the mask with only the lowest bit set.
     46 	 */
     47 	subl	zero, t0, t1
     48 	ldil	v0, 1
     49 	and	t0, t1, t1
     50 
     51 	and	t1, 0xff, t2
     52 	bne	t2, Ldo8
     53 
     54 	/*
     55 	 * If lower 16 bits empty, add 16 to result and use upper 16.
     56 	 */
     57 	zapnot	t1, 0x03, t3
     58 	bne	t3, Ldo16
     59 	sra	t1, 16, t1
     60 	addl	v0, 16, v0
     61 
     62 Ldo16:
     63 	/*
     64 	 * If lower 8 bits empty, add 8 to result and use upper 8.
     65 	 */
     66 	and	t1, 0xff, t4
     67 	bne	t4, Ldo8
     68 	sra	t1, 8, t1
     69 	addl	v0, 8, v0
     70 
     71 Ldo8:
     72 	and	t1, 0x0f, t5		/* lower 4 of 8 empty? */
     73 	and	t1, 0x33, t6		/* lower 2 of each 4 empty? */
     74 	and	t1, 0x55, t7		/* lower 1 of each 2 empty? */
     75 
     76 	/* If lower 4 bits empty, add 4 to result. */
     77 	bne	t5, Ldo4
     78 	addl	v0, 4, v0
     79 
     80 Ldo4:	/* If lower 2 bits of each 4 empty, add 2 to result. */
     81 	bne	t6, Ldo2
     82 	addl	v0, 2, v0
     83 
     84 Ldo2:	/* If lower bit of each 2 empty, add 1 to result. */
     85 	bne	t7, Ldone
     86 	addl	v0, 1, v0
     87 
     88 Ldone:
     89 	RET
     90 
     91 Lallzero:
     92 	bis	zero, zero, v0
     93 	RET
     94 END(ffs)
     95