/* strcat(dest, src) -- Append SRC on the end of DEST. Optimized for x86-64. Copyright (C) 2002-2016 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Andreas Jaeger , 2002. 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 . */ #include #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)