strcpy.S revision 1.1
1 /* 2 * Written by J.T. Conklin <jtc (at) acorntoolworks.com> 3 * Public domain. 4 */ 5 6 #include <machine/asm.h> 7 8 #if defined(LIBC_SCCS) 9 RCSID("$NetBSD: strcpy.S,v 1.1 2005/12/20 19:28:51 christos Exp $") 10 #endif 11 12 /* 13 * This strcpy implementation copies a byte at a time until the 14 * source pointer is aligned to a word boundary, it then copies by 15 * words until it finds a word containing a zero byte, and finally 16 * copies by bytes until the end of the string is reached. 17 * 18 * While this may result in unaligned stores if the source and 19 * destination pointers are unaligned with respect to each other, 20 * it is still faster than either byte copies or the overhead of 21 * an implementation suitable for machines with strict alignment 22 * requirements. 23 */ 24 25 ENTRY(strcpy) 26 movq %rdi,%rax 27 movabsq $0x0101010101010101,%r8 28 movabsq $0x8080808080808080,%r9 29 30 /* 31 * Align source to a word boundary. 32 * Consider unrolling loop? 33 */ 34 _ALIGN_TEXT 35 .Lalign: 36 testb $7,%sil 37 je .Lword_aligned 38 movb (%rsi),%dl 39 incq %rsi 40 movb %dl,(%rdi) 41 incq %rdi 42 testb %dl,%dl 43 jne .Lalign 44 ret 45 46 _ALIGN_TEXT 47 .Lloop: 48 movq %rdx,(%rdi) 49 addq $8,%rdi 50 .Lword_aligned: 51 movq (%rsi),%rdx 52 movq %rdx,%rcx 53 addq $8,%rsi 54 subq %r8,%rcx 55 testq %r9,%rcx 56 je .Lloop 57 58 /* 59 * In rare cases, the above loop may exit prematurely. We must 60 * return to the loop if none of the bytes in the word equal 0. 61 */ 62 63 movb %dl,(%rdi) 64 incq %rdi 65 testb %dl,%dl /* 1st byte == 0? */ 66 je .Ldone 67 68 shrq $8,%rdx 69 movb %dl,(%rdi) 70 incq %rdi 71 testb %dl,%dl /* 2nd byte == 0? */ 72 je .Ldone 73 74 shrq $8,%rdx 75 movb %dl,(%rdi) 76 incq %rdi 77 testb %dl,%dl /* 3rd byte == 0? */ 78 je .Ldone 79 80 shrq $8,%rdx 81 movb %dl,(%rdi) 82 incq %rdi 83 testb %dl,%dl /* 4th byte == 0? */ 84 je .Ldone 85 86 shrq $8,%rdx 87 movb %dl,(%rdi) 88 incq %rdi 89 testb %dl,%dl /* 5th byte == 0? */ 90 je .Ldone 91 92 shrq $8,%rdx 93 movb %dl,(%rdi) 94 incq %rdi 95 testb %dl,%dl /* 6th byte == 0? */ 96 je .Ldone 97 98 shrq $8,%rdx 99 movb %dl,(%rdi) 100 incq %rdi 101 testb %dl,%dl /* 7th byte == 0? */ 102 je .Ldone 103 104 shrq $8,%rdx 105 movb %dl,(%rdi) 106 incq %rdi 107 testb %dl,%dl /* 8th byte == 0? */ 108 jne .Lword_aligned 109 110 .Ldone: 111 ret 112
Indexes created Fri Oct 03 02:09:57 GMT 2025