1/* 2 * Written by J.T. Conklin <jtc@acorntoolworks.com> 3 * Public domain. 4 * 5 * $NetBSD: strcpy.S,v 1.3 2004/07/19 20:04:41 drochner Exp $ 6 * $FreeBSD: src/lib/libc/amd64/string/strcpy.S,v 1.3 2008/11/02 01:10:54 peter Exp $ 7 */ 8 9#include <machine/asm.h> 10 11/* 12 * This strcpy implementation copies a byte at a time until the 13 * source pointer is aligned to a word boundary, it then copies by 14 * words until it finds a word containing a zero byte, and finally 15 * copies by bytes until the end of the string is reached. 16 * 17 * While this may result in unaligned stores if the source and 18 * destination pointers are unaligned with respect to each other, 19 * it is still faster than either byte copies or the overhead of 20 * an implementation suitable for machines with strict alignment 21 * requirements. 22 */ 23 24ENTRY(strcpy) 25 movq %rdi,%rax 26 movabsq $0x0101010101010101,%r8 27 movabsq $0x8080808080808080,%r9 28 29 /* 30 * Align source to a word boundary. 31 * Consider unrolling loop? 32 */ 33.Lalign: 34 testb $7,%sil 35 je .Lword_aligned 36 movb (%rsi),%dl 37 incq %rsi 38 movb %dl,(%rdi) 39 incq %rdi 40 testb %dl,%dl 41 jne .Lalign 42 ret 43 44 .p2align 4 45.Lloop: 46 movq %rdx,(%rdi) 47 addq $8,%rdi 48.Lword_aligned: 49 movq (%rsi),%rdx 50 movq %rdx,%rcx 51 addq $8,%rsi 52 subq %r8,%rcx 53 testq %r9,%rcx 54 je .Lloop 55 56 /* 57 * In rare cases, the above loop may exit prematurely. We must 58 * return to the loop if none of the bytes in the word equal 0. 59 */ 60 61 movb %dl,(%rdi) 62 incq %rdi 63 testb %dl,%dl /* 1st byte == 0? */ 64 je .Ldone 65 66 shrq $8,%rdx 67 movb %dl,(%rdi) 68 incq %rdi 69 testb %dl,%dl /* 2nd byte == 0? */ 70 je .Ldone 71 72 shrq $8,%rdx 73 movb %dl,(%rdi) 74 incq %rdi 75 testb %dl,%dl /* 3rd byte == 0? */ 76 je .Ldone 77 78 shrq $8,%rdx 79 movb %dl,(%rdi) 80 incq %rdi 81 testb %dl,%dl /* 4th byte == 0? */ 82 je .Ldone 83 84 shrq $8,%rdx 85 movb %dl,(%rdi) 86 incq %rdi 87 testb %dl,%dl /* 5th byte == 0? */ 88 je .Ldone 89 90 shrq $8,%rdx 91 movb %dl,(%rdi) 92 incq %rdi 93 testb %dl,%dl /* 6th byte == 0? */ 94 je .Ldone 95 96 shrq $8,%rdx 97 movb %dl,(%rdi) 98 incq %rdi 99 testb %dl,%dl /* 7th byte == 0? */ 100 je .Ldone 101 102 shrq $8,%rdx 103 movb %dl,(%rdi) 104 incq %rdi 105 testb %dl,%dl /* 8th byte == 0? */ 106 jne .Lword_aligned 107 108.Ldone: 109 ret 110END(strcpy) 111