| /* strlen(str) -- determine the length of the string STR. |
| Copyright (C) 2002, 2003 Free Software Foundation, Inc. |
| Based on i486 version contributed by Ulrich Drepper <drepper@redhat.com>. |
| This file is part of the GNU C Library. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, write to the Free |
| Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 02111-1307 USA. */ |
| |
| #include <sysdep.h> |
| #include "asm-syntax.h" |
| #include "bp-sym.h" |
| #include "bp-asm.h" |
| |
| |
| .text |
| ENTRY (strlen) |
| movq %rdi, %rcx /* Duplicate source pointer. */ |
| andl $7, %ecx /* mask alignment bits */ |
| movq %rdi, %rax /* duplicate destination. */ |
| jz 1f /* aligned => start loop */ |
| |
| neg %ecx /* We need to align to 8 bytes. */ |
| addl $8,%ecx |
| /* Search the first bytes directly. */ |
| 0: cmpb $0x0,(%rax) /* is byte NUL? */ |
| je 2f /* yes => return */ |
| incq %rax /* increment pointer */ |
| decl %ecx |
| jnz 0b |
| |
| 1: movq $0xfefefefefefefeff,%r8 /* Save magic. */ |
| |
| .p2align 4 /* Align loop. */ |
| 4: /* Main Loop is unrolled 4 times. */ |
| /* First unroll. */ |
| movq (%rax), %rcx /* get double word (= 8 bytes) in question */ |
| addq $8,%rax /* adjust pointer for next word */ |
| movq %r8, %rdx /* magic value */ |
| addq %rcx, %rdx /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc 3f /* highest byte is NUL => return pointer */ |
| xorq %rcx, %rdx /* (word+magic)^word */ |
| orq %r8, %rdx /* set all non-carry bits */ |
| incq %rdx /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz 3f /* found NUL => return pointer */ |
| |
| /* Second unroll. */ |
| movq (%rax), %rcx /* get double word (= 8 bytes) in question */ |
| addq $8,%rax /* adjust pointer for next word */ |
| movq %r8, %rdx /* magic value */ |
| addq %rcx, %rdx /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc 3f /* highest byte is NUL => return pointer */ |
| xorq %rcx, %rdx /* (word+magic)^word */ |
| orq %r8, %rdx /* set all non-carry bits */ |
| incq %rdx /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz 3f /* found NUL => return pointer */ |
| |
| /* Third unroll. */ |
| movq (%rax), %rcx /* get double word (= 8 bytes) in question */ |
| addq $8,%rax /* adjust pointer for next word */ |
| movq %r8, %rdx /* magic value */ |
| addq %rcx, %rdx /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc 3f /* highest byte is NUL => return pointer */ |
| xorq %rcx, %rdx /* (word+magic)^word */ |
| orq %r8, %rdx /* set all non-carry bits */ |
| incq %rdx /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz 3f /* found NUL => return pointer */ |
| |
| /* Fourth unroll. */ |
| movq (%rax), %rcx /* get double word (= 8 bytes) in question */ |
| addq $8,%rax /* adjust pointer for next word */ |
| movq %r8, %rdx /* magic value */ |
| addq %rcx, %rdx /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc 3f /* highest byte is NUL => return pointer */ |
| xorq %rcx, %rdx /* (word+magic)^word */ |
| orq %r8, %rdx /* set all non-carry bits */ |
| incq %rdx /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jz 4b /* no NUL found => continue loop */ |
| |
| .p2align 4 /* Align, it's a jump target. */ |
| 3: subq $8,%rax /* correct pointer increment. */ |
| |
| testb %cl, %cl /* is first byte NUL? */ |
| jz 2f /* yes => return */ |
| incq %rax /* increment pointer */ |
| |
| testb %ch, %ch /* is second byte NUL? */ |
| jz 2f /* yes => return */ |
| incq %rax /* increment pointer */ |
| |
| testl $0x00ff0000, %ecx /* is third byte NUL? */ |
| jz 2f /* yes => return pointer */ |
| incq %rax /* increment pointer */ |
| |
| testl $0xff000000, %ecx /* is fourth byte NUL? */ |
| jz 2f /* yes => return pointer */ |
| incq %rax /* increment pointer */ |
| |
| shrq $32, %rcx /* look at other half. */ |
| |
| testb %cl, %cl /* is first byte NUL? */ |
| jz 2f /* yes => return */ |
| incq %rax /* increment pointer */ |
| |
| testb %ch, %ch /* is second byte NUL? */ |
| jz 2f /* yes => return */ |
| incq %rax /* increment pointer */ |
| |
| testl $0xff0000, %ecx /* is third byte NUL? */ |
| jz 2f /* yes => return pointer */ |
| incq %rax /* increment pointer */ |
| 2: |
| subq %rdi, %rax /* compute difference to string start */ |
| ret |
| END (strlen) |
| libc_hidden_builtin_def (strlen) |
