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

1.1       nbrk        1: /*     $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $ */
                      2:
                      3: /*-
                      4:  * Copyright (c) 2002 The NetBSD Foundation, Inc.
                      5:  * All rights reserved.
                      6:  *
                      7:  * This code is derived from software contributed to The NetBSD Foundation
                      8:  * by ITOH Yasufumi.
                      9:  *
                     10:  * Redistribution and use in source and binary forms, with or without
                     11:  * modification, are permitted provided that the following conditions
                     12:  * are met:
                     13:  * 1. Redistributions of source code must retain the above copyright
                     14:  *    notice, this list of conditions and the following disclaimer.
                     15:  * 2. Redistributions in binary form must reproduce the above copyright
                     16:  *    notice, this list of conditions and the following disclaimer in the
                     17:  *    documentation and/or other materials provided with the distribution.
                     18:  * 3. All advertising materials mentioning features or use of this software
                     19:  *    must display the following acknowledgement:
                     20:  *     This product includes software developed by the NetBSD
                     21:  *     Foundation, Inc. and its contributors.
                     22:  * 4. Neither the name of The NetBSD Foundation nor the names of its
                     23:  *    contributors may be used to endorse or promote products derived
                     24:  *    from this software without specific prior written permission.
                     25:  *
                     26:  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
                     27:  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
                     28:  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
                     29:  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
                     30:  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
                     31:  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
                     32:  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
                     33:  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
                     34:  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
                     35:  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
                     36:  * POSSIBILITY OF SUCH DAMAGE.
                     37:  */
                     38:
                     39: #include <machine/asm.h>
                     40:
                     41: #if defined(LIBC_SCCS) && !defined(lint)
                     42:        RCSID("$NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $")
                     43: #endif
                     44:
                     45: /*
                     46:  * ffs - find first bit set
                     47:  *
                     48:  * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions.
                     49:  * The remaining 8bit is tested in every 2bit.
                     50:  */
                     51:
                     52: ENTRY(ffs)
                     53:        mov     r4,r0           ! using r0 specific instructions
                     54:        tst     #0xff,r0
                     55:        bf/s    L8bit
                     56:        mov     #0+1,r1         ! ret = 1..8
                     57:
                     58:        tst     r0,r0           ! ffs(0) is 0
                     59:        bt      Lzero           ! testing here to accelerate ret=1..8 cases
                     60:
                     61:        shlr8   r0
                     62:        tst     #0xff,r0
                     63:        bf/s    L8bit
                     64:        mov     #8+1,r1         ! ret = 9..16
                     65:
                     66:        shlr8   r0
                     67:        tst     #0xff,r0
                     68:        bf/s    L8bit
                     69:        mov     #16+1,r1        ! ret = 17..24
                     70:
                     71:        shlr8   r0
                     72:        mov     #24+1,r1        ! ret = 25..32
                     73:
                     74: L8bit:
                     75:        tst     #0x0f,r0
                     76:        bt      4f
                     77:
                     78:        tst     #0x03,r0
                     79:        bt      2f
                     80:        tst     #0x01,r0        ! not bit 0 -> T
                     81:        mov     #0,r0
                     82:        rts
                     83:         addc   r1,r0           ! 0 + r1 + T -> r0
                     84:
                     85: 2:     tst     #0x04,r0
                     86:        mov     #2,r0
                     87:        rts
                     88:         addc   r1,r0
                     89:
                     90: 4:     tst     #0x30,r0
                     91:        bt      6f
                     92:        tst     #0x10,r0
                     93:        mov     #4,r0
                     94:        rts
                     95:         addc   r1,r0
                     96:
                     97: 6:     tst     #0x40,r0
                     98:        mov     #6,r0
                     99:        rts
                    100:         addc   r1,r0
                    101:
                    102: Lzero: rts
                    103:         nop