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Annotation of src/lib/libc/arch/hppa/string/ffs.S, Revision 1.1

1.1     ! fredette    1: /*     $NetBSD$        */
        !             2:
        !             3: /*     $OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $  */
        !             4:
        !             5: /*
        !             6:  * Copyright (c) 1990, 1991, 1992, 1994, The University of Utah and
        !             7:  * the Computer Systems Laboratory at the University of Utah (CSL).
        !             8:  * All rights reserved.
        !             9:  *
        !            10:  * Permission to use, copy, modify and distribute this software and its
        !            11:  * documentation is hereby granted, provided that both the copyright
        !            12:  * notice and this permission notice appear in all copies of the
        !            13:  * software, derivative works or modified versions, and any portions
        !            14:  * thereof, and that both notices appear in supporting documentation.
        !            15:  *
        !            16:  * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
        !            17:  * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF
        !            18:  * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
        !            19:  *
        !            20:  * CSL requests users of this software to return to csl-dist@cs.utah.edu any
        !            21:  * improvements that they make and grant CSL redistribution rights.
        !            22:  *
        !            23:  */
        !            24:
        !            25: #include <machine/asm.h>
        !            26:
        !            27: #ifdef SYSLIBC_SCCS
        !            28:        .text
        !            29:        .asciz "$OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $"
        !            30:        .align  4
        !            31: #endif
        !            32:
        !            33: /*
        !            34:  * ffs(bitmask)
        !            35:  *
        !            36:  * Return the position of the "most significant" bit in `bitmask'.
        !            37:  * Since this is similar to the VAX ffs instruction, bits in a word
        !            38:  * are numbered as "32, 31, ... 1", 0 is returned if no bits are set.
        !            39:  */
        !            40:
        !            41: LEAF_ENTRY(ffs)
        !            42:        comb,=  arg0,r0,ffsdone         ; If arg0 is 0
        !            43:        or      r0,r0,ret0              ;   return 0
        !            44:        ldi     32,ret0                 ; Set return to high bit
        !            45:        extru,= arg0,31,16,r0           ; If low 16 bits are non-zero
        !            46:        addi,tr -16,ret0,ret0           ;   subtract 16 from bitpos
        !            47:        shd     r0,arg0,16,arg0         ; else shift right 16 bits
        !            48:        extru,= arg0,31,8,r0            ; If low 8 bits are non-zero
        !            49:        addi,tr -8,ret0,ret0            ;   subtract 8 from bitpos
        !            50:        shd     r0,arg0,8,arg0          ; else shift right 8 bits
        !            51:        extru,= arg0,31,4,r0            ; If low 4 bits are non-zero
        !            52:        addi,tr -4,ret0,ret0            ;   subtract 4 from bitpos
        !            53:        shd     r0,arg0,4,arg0          ; else shift right 4 bits
        !            54:        extru,= arg0,31,2,r0            ; If low 2 bits are non-zero
        !            55:        addi,tr -2,ret0,ret0            ;   subtract 2 from bitpos
        !            56:        shd     r0,arg0,2,arg0          ; else shift right 2 bits
        !            57:        extru,= arg0,31,1,r0            ; If low bit is non-zero
        !            58:        addi    -1,ret0,ret0            ;   subtract 1 from bitpos
        !            59: ffsdone:
        !            60: EXIT(ffs)
        !            61:
        !            62:        .end