/* $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:49 christos Exp $ */

/*
* Copyright (c) 1995 Christopher G. Demetriou
* 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 for the
*          NetBSD Project.  See http://www.NetBSD.org/ for
*          information about NetBSD.
* 4. The name of the author may not be used to endorse or promote products
*    derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
*
* <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
*/

#include <machine/asm.h>

LEAF(ffs, 1)
       addl    a0, 0, t0
       beq     t0, Lallzero

       /*
        * Initialize return value (v0), and set up t1 so that it
        * contains the mask with only the lowest bit set.
        */
       subl    zero, t0, t1
       ldil    v0, 1
       and     t0, t1, t1

       and     t1, 0xff, t2
       bne     t2, Ldo8

       /*
        * If lower 16 bits empty, add 16 to result and use upper 16.
        */
       zapnot  t1, 0x03, t3
       bne     t3, Ldo16
       sra     t1, 16, t1
       addl    v0, 16, v0

Ldo16:
       /*
        * If lower 8 bits empty, add 8 to result and use upper 8.
        */
       and     t1, 0xff, t4
       bne     t4, Ldo8
       sra     t1, 8, t1
       addl    v0, 8, v0

Ldo8:
       and     t1, 0x0f, t5            /* lower 4 of 8 empty? */
       and     t1, 0x33, t6            /* lower 2 of each 4 empty? */
       and     t1, 0x55, t7            /* lower 1 of each 2 empty? */

       /* If lower 4 bits empty, add 4 to result. */
       bne     t5, Ldo4
       addl    v0, 4, v0

Ldo4:   /* If lower 2 bits of each 4 empty, add 2 to result. */
       bne     t6, Ldo2
       addl    v0, 2, v0

Ldo2:   /* If lower bit of each 2 empty, add 1 to result. */
       bne     t7, Ldone
       addl    v0, 1, v0

Ldone:
       RET

Lallzero:
       bis     zero, zero, v0
       RET
END(ffs)