109 lines
3.6 KiB
ArmAsm
109 lines
3.6 KiB
ArmAsm
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/* $NetBSD: memchr.S,v 1.5 2009/08/01 20:47:02 dsl Exp $ */
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/*-
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* Copyright (c) 2009 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by David Laight.
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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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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <machine/asm.h>
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#if defined(LIBC_SCCS)
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RCSID("$NetBSD: memchr.S,v 1.5 2009/08/01 20:47:02 dsl Exp $")
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#endif
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/*
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* The instruction sequences used try to avoid data dependencies
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* between adjacent instructions (to allow parallel execution).
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* The 'imul' for %r9 could be put into the delay following the
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* memory read (ie inside the loop) at no obvious cost - except
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* that the loop is currently exactly 32 bytes - 2 fetch blocks!.
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*
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* I don't think aligning any of the other branch targets is useful.
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*/
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ENTRY(memchr)
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movabsq $0x0101010101010101,%r8
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lea (%rdi,%rdx),%r10 /* limit of buffer to scan */
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movzbq %sil,%rsi /* mask high bits! */
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/* 'directpath' imuls can execute 3 at a time ... (amd) */
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imul %r8,%rsi /* search byte replicated in word */
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imul $0x80,%r8,%r9 /* 0x8080808080808080 */
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test $7,%dil
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jnz 20f /* jump if misaligned */
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jmp 1f /* jump to avoid 4 nops (13 bytes) in gap */
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_ALIGN_TEXT /* entire loop now in 32 aligned bytes */
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1:
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cmpq %r10,%rdi /* end of buffer ? */
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jae 30f /* jump if so */
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movq (%rdi),%rax /* value to check */
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addq $8,%rdi
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xorq %rsi,%rax /* now looking for zeros */
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2:
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mov %rax,%rcx
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subq %r8,%rax /* x - 0x01 */
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not %rcx
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andq %r9,%rax /* (x - 0x01) & 0x80 */
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andq %rcx,%rax /* ((x - 0x01) & 0x80) & ~x */
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je 1b /* jump if not found */
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/* Found byte in word, get its address */
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bsf %rax,%rax
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shr $3,%eax
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lea -8(%rax,%rdi),%rax
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cmpq %r10,%rax /* need to check not beyond buffer */
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jae 30f
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rep
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ret /* amd - no ret after jmp */
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/* Input misaligned, read aligned and make low bytes invalid */
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20:
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mov %dil,%cl /* misalignment amount 1..7 (+high bits )*/
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and $~7,%dil /* %rdi now start of word */
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test %rdx,%rdx /* zero length, don't read */
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jz 30f
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neg %cl /* 7..1 (+high bits) */
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mov (%rdi),%rax /* word containing first byte */
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addq $8,%rdi
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and $7,%cl /* 7..1 */
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mov %r8,%r11 /* any value with bits in each byte */
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shl $3,%cl /* 56..8 */
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xorq %rsi,%rax /* now looking for zeros */
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/* Set low bytes non-zero */
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shr %cl,%r11 /* non-zero in unwanted bytes */
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or %r11,%rax /* low bytes now set */
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jmp 2b
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/* Not found */
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30: xorq %rax,%rax
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ret
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