diff options
Diffstat (limited to 'libc/string/x86_64/strlen.S')
| -rw-r--r-- | libc/string/x86_64/strlen.S | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/libc/string/x86_64/strlen.S b/libc/string/x86_64/strlen.S new file mode 100644 index 000000000..36b63031e --- /dev/null +++ b/libc/string/x86_64/strlen.S @@ -0,0 +1,135 @@ +/* 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 "_glibc_inc.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) |