b6cbf7203b
This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
119 lines
4.6 KiB
ArmAsm
119 lines
4.6 KiB
ArmAsm
/* $NetBSD: strlen.S,v 1.6 2011/01/15 07:31:12 matt Exp $ */
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/*-
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* Copyright (C) 2001 Martin J. Laubach <mjl@NetBSD.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*----------------------------------------------------------------------*/
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#include <machine/asm.h>
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__RCSID("$NetBSD: strlen.S,v 1.6 2011/01/15 07:31:12 matt Exp $");
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/*----------------------------------------------------------------------*/
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/* The algorithm here uses the following techniques:
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1) Given a word 'x', we can test to see if it contains any 0 bytes
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by subtracting 0x01010101, and seeing if any of the high bits of each
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byte changed from 0 to 1. This works because the least significant
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0 byte must have had no incoming carry (otherwise it's not the least
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significant), so it is 0x00 - 0x01 == 0xff. For all other
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byte values, either they have the high bit set initially, or when
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1 is subtracted you get a value in the range 0x00-0x7f, none of which
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have their high bit set. The expression here is
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(x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
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there were no 0x00 bytes in the word.
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2) Given a word 'x', we can test to see _which_ byte was zero by
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calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f).
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This produces 0x80 in each byte that was zero, and 0x00 in all
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the other bytes. The '| 0x7f7f7f7f' clears the low 7 bits in each
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byte, and the '| x' part ensures that bytes with the high bit set
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produce 0x00. The addition will carry into the high bit of each byte
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iff that byte had one of its low 7 bits set. We can then just see
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which was the most significant bit set and divide by 8 to find how
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many to add to the index.
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This is from the book 'The PowerPC Compiler Writer's Guide',
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by Steve Hoxey, Faraydon Karim, Bill Hay and Hank Warren.
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*/
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/*----------------------------------------------------------------------*/
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.text
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.align 4
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ENTRY(strlen)
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/* Setup constants */
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lis %r10, 0x7f7f
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lis %r9, 0xfefe
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ori %r10, %r10, 0x7f7f
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ori %r9, %r9, 0xfeff
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/* Mask out leading bytes on non aligned strings */
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rlwinm. %r8, %r3, 3, 27, 28 /* leading bits to mask */
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#ifdef _LP64
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clrrdi %r5, %r3, 2 /* clear low 2 addr bits */
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#else
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clrrwi %r5, %r3, 2 /* clear low 2 addr bits */
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#endif
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li %r0, -1
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beq+ 3f /* skip alignment if already */
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/* aligned */
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srw %r0, %r0, %r8 /* make 0000...1111 mask */
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lwz %r7, 0(%r5)
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nor %r0, %r0, %r0 /* invert mask */
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or %r7, %r7, %r0 /* make leading bytes != 0 */
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b 2f
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3: subi %r5, %r5, 4
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1: lwzu %r7, 4(%r5) /* fetch data word */
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2: nor %r0, %r7, %r10 /* do step 1 */
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add %r6, %r7, %r9
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and. %r0, %r0, %r6
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beq+ 1b /* no NUL bytes here */
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and %r8, %r7, %r10 /* ok, a NUL is somewhere */
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or %r7, %r7, %r10 /* do step 2 to find out */
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add %r0, %r8, %r10 /* where */
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nor %r8, %r7, %r0
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cntlzw %r0, %r8 /* offset from this word */
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srwi %r4, %r0, 3
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add %r4, %r5, %r4 /* r4 contains end pointer */
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/* NOTE: Keep it so this function returns the end pointer
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in r4, so we can it use from other str* calls (strcat
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comes to mind */
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subf %r3, %r3, %r4
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blr
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END(strlen)
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/*----------------------------------------------------------------------*/
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