| /* $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. |
| * 3. All advertising materials mentioning features or use of this software |
| * must display the following acknowledgement: |
| * This product includes software developed by the NetBSD |
| * Foundation, Inc. and its contributors. |
| * 4. Neither the name of The NetBSD Foundation nor the names of its |
| * contributors may be used to endorse or promote products derived |
| * from this software without specific prior written permission. |
| * |
| * 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 <machine/asm.h> |
| |
| #if defined(LIBC_SCCS) && !defined(lint) |
| RCSID("$NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $") |
| #endif |
| |
| /* |
| * 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 |
