/* 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, see <http://www.gnu.org/licenses/>. */ #include "_glibc_inc.h" /* Seems to be unrolled too much */ .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. */ /* Align loop. */ /* Next 3 insns are 10 bytes total, make sure we decode them in one go */ .p2align 4,,10 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 */ /* Align, it is a jump target. */ /* Next 3 insns are 8 bytes total, make sure we decode them in one go */ .p2align 3,,8 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_def(strlen)