137 lines
4.8 KiB
ArmAsm
137 lines
4.8 KiB
ArmAsm
/* strlen(str) -- determine the length of the string STR.
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Copyright (C) 2002-2015 Free Software Foundation, Inc.
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Based on i486 version contributed by Ulrich Drepper <drepper@redhat.com>.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include "asm-syntax.h"
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.text
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ENTRY (strlen)
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movq %rdi, %rcx /* Duplicate source pointer. */
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andl $7, %ecx /* mask alignment bits */
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movq %rdi, %rax /* duplicate destination. */
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jz 1f /* aligned => start loop */
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neg %ecx /* We need to align to 8 bytes. */
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addl $8,%ecx
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/* Search the first bytes directly. */
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0: cmpb $0x0,(%rax) /* is byte NUL? */
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je 2f /* yes => return */
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incq %rax /* increment pointer */
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decl %ecx
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jnz 0b
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1: movq $0xfefefefefefefeff,%r8 /* Save magic. */
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.p2align 4 /* Align loop. */
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4: /* Main Loop is unrolled 4 times. */
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/* First unroll. */
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movq (%rax), %rcx /* get double word (= 8 bytes) in question */
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addq $8,%rax /* adjust pointer for next word */
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movq %r8, %rdx /* magic value */
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addq %rcx, %rdx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc 3f /* highest byte is NUL => return pointer */
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xorq %rcx, %rdx /* (word+magic)^word */
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orq %r8, %rdx /* set all non-carry bits */
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incq %rdx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz 3f /* found NUL => return pointer */
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/* Second unroll. */
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movq (%rax), %rcx /* get double word (= 8 bytes) in question */
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addq $8,%rax /* adjust pointer for next word */
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movq %r8, %rdx /* magic value */
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addq %rcx, %rdx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc 3f /* highest byte is NUL => return pointer */
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xorq %rcx, %rdx /* (word+magic)^word */
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orq %r8, %rdx /* set all non-carry bits */
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incq %rdx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz 3f /* found NUL => return pointer */
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/* Third unroll. */
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movq (%rax), %rcx /* get double word (= 8 bytes) in question */
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addq $8,%rax /* adjust pointer for next word */
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movq %r8, %rdx /* magic value */
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addq %rcx, %rdx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc 3f /* highest byte is NUL => return pointer */
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xorq %rcx, %rdx /* (word+magic)^word */
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orq %r8, %rdx /* set all non-carry bits */
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incq %rdx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz 3f /* found NUL => return pointer */
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/* Fourth unroll. */
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movq (%rax), %rcx /* get double word (= 8 bytes) in question */
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addq $8,%rax /* adjust pointer for next word */
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movq %r8, %rdx /* magic value */
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addq %rcx, %rdx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc 3f /* highest byte is NUL => return pointer */
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xorq %rcx, %rdx /* (word+magic)^word */
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orq %r8, %rdx /* set all non-carry bits */
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incq %rdx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jz 4b /* no NUL found => continue loop */
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.p2align 4 /* Align, it's a jump target. */
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3: subq $8,%rax /* correct pointer increment. */
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testb %cl, %cl /* is first byte NUL? */
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jz 2f /* yes => return */
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incq %rax /* increment pointer */
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testb %ch, %ch /* is second byte NUL? */
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jz 2f /* yes => return */
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incq %rax /* increment pointer */
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testl $0x00ff0000, %ecx /* is third byte NUL? */
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jz 2f /* yes => return pointer */
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incq %rax /* increment pointer */
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testl $0xff000000, %ecx /* is fourth byte NUL? */
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jz 2f /* yes => return pointer */
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incq %rax /* increment pointer */
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shrq $32, %rcx /* look at other half. */
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testb %cl, %cl /* is first byte NUL? */
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jz 2f /* yes => return */
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incq %rax /* increment pointer */
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testb %ch, %ch /* is second byte NUL? */
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jz 2f /* yes => return */
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incq %rax /* increment pointer */
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testl $0xff0000, %ecx /* is third byte NUL? */
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jz 2f /* yes => return pointer */
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incq %rax /* increment pointer */
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2:
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subq %rdi, %rax /* compute difference to string start */
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ret
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END (strlen)
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libc_hidden_builtin_def (strlen)
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