Return to ffs.S CVS log

Up to [local] / sys / lib / libkern / arch / alpha

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