5863 psiginfo arguments should be const
[unleashed.git] / usr / src / lib / libc / i386 / gen / strncpy.s
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1 /*
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22 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
23 * Use is subject to license terms.
26 .file "strncpy.s"
29 / strncpy(s1, s2, n)
31 / Copies s2 to s1, truncating or null-padding to always copy n bytes
32 / Returns s1
34 / Fast assembly language version of the following C-program strncpy
35 / which represents the `standard' for the C-library.
37 / char *
38 / strncpy(char *s1, const char *s2, size_t n)
39 / {
40 / char *os1 = s1;
42 / n++;
43 / while ((--n != 0) && ((*s1++ = *s2++) != '\0'))
44 / ;
45 / if (n != 0)
46 / while (--n != 0)
47 / *s1++ = '\0';
48 / return (os1);
49 / }
51 / In this assembly language version, the following expression is used
52 / to check if a 32-bit word data contains a null byte or not:
53 / (((A & 0x7f7f7f7f) + 0x7f7f7f7f) | A) & 0x80808080
54 / If the above expression geneates a value other than 0x80808080,
55 / that means the 32-bit word data contains a null byte.
58 / Assume relatively long strings and small numbers of nulls at end.
60 #include "SYS.h"
62 ENTRY(strncpy)
63 pushl %edi / save register variables
64 pushl %esi
66 movl 16(%esp), %eax / %eax = source string address
67 movl 12(%esp), %edi / %edi = destination string address
68 movl 20(%esp), %esi / %esi = number of bytes
70 testl $3, %eax / if %eax not word aligned
71 jnz .L1 / goto .L1
72 .L8:
73 cmpl $4, %esi / if number of bytes < 4
74 jb .L4 / goto .L4
75 .align 4
76 .L2:
77 movl (%eax), %edx / move 1 word from (%eax) to %edx
78 movl $0x7f7f7f7f, %ecx
79 andl %edx, %ecx / %ecx = %edx & 0x7f7f7f7f
80 addl $4, %eax / next word
81 addl $0x7f7f7f7f, %ecx / %ecx += 0x7f7f7f7f
82 orl %edx, %ecx / %ecx |= %edx
83 andl $0x80808080, %ecx / %ecx &= 0x80808080
84 cmpl $0x80808080, %ecx / if null byte in this word
85 jne .L3 / goto .L3
86 movl %edx, (%edi) / copy this word to (%edi)
87 subl $4, %esi / decrement number of bytes by 4
88 addl $4, %edi / next word
89 cmpl $4, %esi / if number of bytes >= 4
90 jae .L2 / goto .L2
91 jmp .L4 / goto .L4
92 .L3:
93 subl $4, %eax / post-incremented
94 .align 4
95 .L4:
96 / (number of bytes < 4) or (a null byte found in the word)
97 cmpl $0, %esi / if number of bytes == 0
98 je .L7 / goto .L7 (finished)
99 movb (%eax), %dl / %dl = a byte in (%eax)
100 decl %esi / decrement number of bytes by 1
101 movb %dl, (%edi) / copy %dl to (%edi)
102 incl %eax / next byte
103 incl %edi / next byte
104 cmpb $0, %dl / compare %dl with a null byte
105 je .L5 / if %dl is a null, goto .L5
106 jmp .L4 / goto .L4
107 .align 4
108 .L1:
109 / %eax not aligned
110 cmpl $0, %esi / if number of bytes == 0
111 je .L7 / goto .L7 (finished)
112 movb (%eax), %dl / %dl = a byte in (%eax)
113 decl %esi / decrement number of bytes by 1
114 movb %dl, (%edi) / copy %dl to (%edi)
115 incl %edi / next byte
116 incl %eax / next byte
117 cmpb $0, %dl / compare %dl with a null byte
118 je .L5 / if %dl is a null, goto .L5
119 testl $3, %eax / if %eax word aligned
120 jz .L8 / goto .L8
121 jmp .L1 / goto .L1 (not word aligned)
122 .align 4
123 .L5:
124 movl %esi, %ecx / %ecx = length to copy null bytes
125 xorl %eax, %eax / clear %eax
126 shrl $2, %ecx / %ecx = words to copy null bytes
127 rep ; sstol / rep;sstol is optimal
128 andl $3, %esi / %esi = leftover bytes
129 .L6:
130 cmpl $0, %esi / if number of bytes == 0
131 jz .L7 / goto .L7 (finished)
132 movb $0, (%edi) / move a null byte to (%edi)
133 decl %esi / decrement number of bytes by 1
134 incl %edi / next byte
135 jmp .L6 / goto .L6
136 .align 4
137 .L7:
138 movl 12(%esp), %eax / return the destination address
139 popl %esi / restore register variables
140 popl %edi
142 SET_SIZE(strncpy)