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Annotation of sys/lib/libkern/arch/alpha/ffs.S, Revision 1.1.1.1

1.1       nbrk        1: /*     $OpenBSD: ffs.S,v 1.1 1996/10/31 00:43:18 niklas Exp $  */
                      2: /*     $NetBSD: ffs.S,v 1.3 1996/10/17 04:26:26 cgd Exp $      */
                      3:
                      4: /*
                      5:  * Copyright (c) 1995 Christopher G. Demetriou
                      6:  * All rights reserved.
                      7:  *
                      8:  * Redistribution and use in source and binary forms, with or without
                      9:  * modification, are permitted provided that the following conditions
                     10:  * are met:
                     11:  * 1. Redistributions of source code must retain the above copyright
                     12:  *    notice, this list of conditions and the following disclaimer.
                     13:  * 2. Redistributions in binary form must reproduce the above copyright
                     14:  *    notice, this list of conditions and the following disclaimer in the
                     15:  *    documentation and/or other materials provided with the distribution.
                     16:  * 3. All advertising materials mentioning features or use of this software
                     17:  *    must display the following acknowledgement:
                     18:  *      This product includes software developed by Christopher G. Demetriou
                     19:  *     for the NetBSD Project.
                     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:
                     35: #include <machine/asm.h>
                     36:
                     37: LEAF(ffs, 1)
                     38:        addl    a0, 0, t0
                     39:        beq     t0, Lallzero
                     40:
                     41:        /*
                     42:         * Initialize return value (v0), and set up t1 so that it
                     43:         * contains the mask with only the lowest bit set.
                     44:         */
                     45:        subl    zero, t0, t1
                     46:        ldil    v0, 1
                     47:        and     t0, t1, t1
                     48:
                     49:        and     t1, 0xff, t2
                     50:        bne     t2, Ldo8
                     51:
                     52:        /*
                     53:         * If lower 16 bits empty, add 16 to result and use upper 16.
                     54:         */
                     55:        zapnot  t1, 0x03, t3
                     56:        bne     t3, Ldo16
                     57:        sra     t1, 16, t1
                     58:        addl    v0, 16, v0
                     59:
                     60: Ldo16:
                     61:        /*
                     62:         * If lower 8 bits empty, add 8 to result and use upper 8.
                     63:         */
                     64:        and     t1, 0xff, t4
                     65:        bne     t4, Ldo8
                     66:        sra     t1, 8, t1
                     67:        addl    v0, 8, v0
                     68:
                     69: Ldo8:
                     70:        and     t1, 0x0f, t5            /* lower 4 of 8 empty? */
                     71:        and     t1, 0x33, t6            /* lower 2 of each 4 empty? */
                     72:        and     t1, 0x55, t7            /* lower 1 of each 2 empty? */
                     73:
                     74:        /* If lower 4 bits empty, add 4 to result. */
                     75:        bne     t5, Ldo4
                     76:        addl    v0, 4, v0
                     77:
                     78: Ldo4:  /* If lower 2 bits of each 4 empty, add 2 to result. */
                     79:        bne     t6, Ldo2
                     80:        addl    v0, 2, v0
                     81:
                     82: Ldo2:  /* If lower bit of each 2 empty, add 1 to result. */
                     83:        bne     t7, Ldone
                     84:        addl    v0, 1, v0
                     85:
                     86: Ldone:
                     87:        RET
                     88:
                     89: Lallzero:
                     90:        bis     zero, zero, v0
                     91:        RET
                     92: END(ffs)