/*      $OpenBSD: ffs.S,v 1.5 2018/01/23 17:11:02 deraadt Exp $ */
/*      $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $ */

/*-
 * Copyright (c) 2002 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by ITOH Yasufumi.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``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 FOUNDATION OR CONTRIBUTORS
 * 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.
 */

#include "SYS.h"

/*
 * ffs - find first bit set
 *
 * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions.
 * The remaining 8bit is tested in every 2bit.
 */

ENTRY(ffs)
        mov     r4,r0           ! using r0 specific instructions
        tst     #0xff,r0
        bf/s    L8bit
        mov     #0+1,r1         ! ret = 1..8

        tst     r0,r0           ! ffs(0) is 0
        bt      Lzero           ! testing here to accelerate ret=1..8 cases

        shlr8   r0
        tst     #0xff,r0
        bf/s    L8bit
        mov     #8+1,r1         ! ret = 9..16

        shlr8   r0
        tst     #0xff,r0
        bf/s    L8bit
        mov     #16+1,r1        ! ret = 17..24

        shlr8   r0
        mov     #24+1,r1        ! ret = 25..32

L8bit:
        tst     #0x0f,r0
        bt      4f

        tst     #0x03,r0
        bt      2f
        tst     #0x01,r0        ! not bit 0 -> T
        mov     #0,r0
        rts
         addc   r1,r0           ! 0 + r1 + T -> r0

2:      tst     #0x04,r0
        mov     #2,r0
        rts
         addc   r1,r0

4:      tst     #0x30,r0
        bt      6f
        tst     #0x10,r0
        mov     #4,r0
        rts
         addc   r1,r0

6:      tst     #0x40,r0
        mov     #6,r0
        rts
         addc   r1,r0

Lzero:  rts
         nop
END_STRONG(ffs)
.protected ffs