1/*
2 * Written by J.T. Conklin <jtc@acorntoolworks.com>
3 * Public domain.
4 */
5
6#include <machine/asm.h>
7
8#if defined(LIBC_SCCS)
9          RCSID("$NetBSD: strcpy.S,v 1.2 2014/03/22 19:38:46 jakllsch 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
25ENTRY(strcpy)
26          pushl     %ebx
27          movl      8(%esp),%ecx
28          movl      12(%esp),%eax
29
30          /*
31           * Align source to a word boundary.
32           * Consider unrolling loop?
33           */
34          _ALIGN_TEXT
35.Lalign:
36          testl     $3,%eax
37          je        .Lword_aligned
38          movb      (%eax),%bl
39          incl      %eax
40          movb      %bl,(%ecx)
41          incl      %ecx
42          testb     %bl,%bl
43          jne       .Lalign
44          jmp       .Ldone
45
46          _ALIGN_TEXT
47.Lloop:
48          movl      %ebx,(%ecx)
49          addl      $4,%ecx
50.Lword_aligned:
51          movl      (%eax),%ebx
52          addl      $4,%eax
53          leal      -0x01010101(%ebx),%edx
54          testl     $0x80808080,%edx
55          je        .Lloop
56
57          /*
58           * In rare cases, the above loop may exit prematurely. We must
59           * return to the loop if none of the bytes in the word equal 0.
60           */
61
62          movb      %bl,(%ecx)
63          incl      %ecx
64          testb     %bl,%bl
65          je        .Ldone
66
67          movb      %bh,(%ecx)
68          incl      %ecx
69          testb     %bh,%bh
70          je        .Ldone
71
72          shrl      $16,%ebx
73          movb      %bl,(%ecx)
74          incl      %ecx
75          testb     %bl,%bl
76          je        .Ldone
77
78          movb      %bh,(%ecx)
79          incl      %ecx
80          testb     %bh,%bh
81          jne       .Lword_aligned
82
83.Ldone:
84          movl      8(%esp),%eax
85          popl      %ebx
86          ret
87END(strcpy)
88