/*      $NetBSD: ffs.S,v 1.5 2020/05/05 06:20:55 skrll Exp $    */

/*      $OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $  */

/*
 * Copyright (c) 1990, 1991, 1992, 1994, The University of Utah and
 * the Computer Systems Laboratory at the University of Utah (CSL).
 * All rights reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
 * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF
 * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * CSL requests users of this software to return to csl-dist@cs.utah.edu any
 * improvements that they make and grant CSL redistribution rights.
 *
 */

#include <machine/asm.h>

#ifdef SYSLIBC_SCCS
        .text
        .asciz "$OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $"
        .align  4
#endif

/*
 * ffs(bitmask)
 *
 * Return the position of the "most significant" bit in `bitmask'.
 * Since this is similar to the VAX ffs instruction, bits in a word
 * are numbered as "32, 31, ... 1", 0 is returned if no bits are set.
 */

LEAF_ENTRY(ffs)
        comb,=  %arg0,%r0,ffsdone       ; If arg0 is 0
         or     %r0,%r0,%ret0           ;   return 0
        ldi     32,%ret0                ; Set return to high bit
        extru,= %arg0,31,16,%r0         ; If low 16 bits are non-zero
        addi,tr -16,%ret0,%ret0         ;   subtract 16 from bitpos
        shd     %r0,%arg0,16,%arg0      ; else shift right 16 bits
        extru,= %arg0,31,8,%r0          ; If low 8 bits are non-zero
        addi,tr -8,%ret0,%ret0          ;   subtract 8 from bitpos
        shd     %r0,%arg0,8,%arg0       ; else shift right 8 bits
        extru,= %arg0,31,4,%r0          ; If low 4 bits are non-zero
        addi,tr -4,%ret0,%ret0          ;   subtract 4 from bitpos
        shd     %r0,%arg0,4,%arg0       ; else shift right 4 bits
        extru,= %arg0,31,2,%r0          ; If low 2 bits are non-zero
        addi,tr -2,%ret0,%ret0          ;   subtract 2 from bitpos
        shd     %r0,%arg0,2,%arg0       ; else shift right 2 bits
        extru,= %arg0,31,1,%r0          ; If low bit is non-zero
        addi    -1,%ret0,%ret0          ;   subtract 1 from bitpos
ffsdone:
        bv,n    %r0(%rp)
EXIT(ffs)

        .end