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/* strcat(dest, src) -- Append SRC on the end of DEST.
Optimized for x86-64.
Copyright (C) 2002-2021 Free Software Foundation, Inc.
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
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include "asm-syntax.h"
/* Will be removed when new strcpy implementation gets merged. */
.text
ENTRY (strcat)
movq %rdi, %rcx /* Dest. register. */
andl $7, %ecx /* mask alignment bits */
movq %rdi, %rax /* Duplicate destination pointer. */
movq $0xfefefefefefefeff,%r8
/* First step: Find end of destination. */
jz 4f /* 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 => start copy */
incq %rax /* increment pointer */
decl %ecx
jnz 0b
/* Now the source is aligned. Scan for NUL byte. */
.p2align 4
4:
/* 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:
/* Second step: Copy source to destination. */
movq %rsi, %rcx /* duplicate */
andl $7,%ecx /* mask alignment bits */
movq %rax, %rdx /* move around */
jz 22f /* aligned => start loop */
neg %ecx /* align to 8 bytes. */
addl $8, %ecx
/* Align the source pointer. */
21:
movb (%rsi), %al /* Fetch a byte */
testb %al, %al /* Is it NUL? */
movb %al, (%rdx) /* Store it */
jz 24f /* If it was NUL, done! */
incq %rsi
incq %rdx
decl %ecx
jnz 21b
/* Now the sources is aligned. Unfortunatly we cannot force
to have both source and destination aligned, so ignore the
alignment of the destination. */
.p2align 4
22:
/* 1st unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
/* 2nd unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
/* 3rd unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
/* 4th unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
jmp 22b /* Next iteration. */
/* Do the last few bytes. %rax contains the value to write.
The loop is unrolled twice. */
.p2align 4
23:
movb %al, (%rdx) /* 1st byte. */
testb %al, %al /* Is it NUL. */
jz 24f /* yes, finish. */
incq %rdx /* Increment destination. */
movb %ah, (%rdx) /* 2nd byte. */
testb %ah, %ah /* Is it NUL?. */
jz 24f /* yes, finish. */
incq %rdx /* Increment destination. */
shrq $16, %rax /* Shift... */
jmp 23b /* and look at next two bytes in %rax. */
24:
movq %rdi, %rax /* Source is return value. */
retq
END (strcat)
libc_hidden_builtin_def (strcat)
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