minix/common/lib/libc/arch/x86_64/string/memchr.S

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/* $NetBSD: memchr.S,v 1.5 2009/08/01 20:47:02 dsl Exp $ */
/*-
* Copyright (c) 2009 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by David Laight.
*
* 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 <machine/asm.h>
#if defined(LIBC_SCCS)
RCSID("$NetBSD: memchr.S,v 1.5 2009/08/01 20:47:02 dsl Exp $")
#endif
/*
* The instruction sequences used try to avoid data dependencies
* between adjacent instructions (to allow parallel execution).
* The 'imul' for %r9 could be put into the delay following the
* memory read (ie inside the loop) at no obvious cost - except
* that the loop is currently exactly 32 bytes - 2 fetch blocks!.
*
* I don't think aligning any of the other branch targets is useful.
*/
ENTRY(memchr)
movabsq $0x0101010101010101,%r8
lea (%rdi,%rdx),%r10 /* limit of buffer to scan */
movzbq %sil,%rsi /* mask high bits! */
/* 'directpath' imuls can execute 3 at a time ... (amd) */
imul %r8,%rsi /* search byte replicated in word */
imul $0x80,%r8,%r9 /* 0x8080808080808080 */
test $7,%dil
jnz 20f /* jump if misaligned */
jmp 1f /* jump to avoid 4 nops (13 bytes) in gap */
_ALIGN_TEXT /* entire loop now in 32 aligned bytes */
1:
cmpq %r10,%rdi /* end of buffer ? */
jae 30f /* jump if so */
movq (%rdi),%rax /* value to check */
addq $8,%rdi
xorq %rsi,%rax /* now looking for zeros */
2:
mov %rax,%rcx
subq %r8,%rax /* x - 0x01 */
not %rcx
andq %r9,%rax /* (x - 0x01) & 0x80 */
andq %rcx,%rax /* ((x - 0x01) & 0x80) & ~x */
je 1b /* jump if not found */
/* Found byte in word, get its address */
bsf %rax,%rax
shr $3,%eax
lea -8(%rax,%rdi),%rax
cmpq %r10,%rax /* need to check not beyond buffer */
jae 30f
rep
ret /* amd - no ret after jmp */
/* Input misaligned, read aligned and make low bytes invalid */
20:
mov %dil,%cl /* misalignment amount 1..7 (+high bits )*/
and $~7,%dil /* %rdi now start of word */
test %rdx,%rdx /* zero length, don't read */
jz 30f
neg %cl /* 7..1 (+high bits) */
mov (%rdi),%rax /* word containing first byte */
addq $8,%rdi
and $7,%cl /* 7..1 */
mov %r8,%r11 /* any value with bits in each byte */
shl $3,%cl /* 56..8 */
xorq %rsi,%rax /* now looking for zeros */
/* Set low bytes non-zero */
shr %cl,%r11 /* non-zero in unwanted bytes */
or %r11,%rax /* low bytes now set */
jmp 2b
/* Not found */
30: xorq %rax,%rax
ret