1 /* copy no more then N bytes from SRC to DEST, returning the address of
2 the terminating '\0' in DEST.
4 Copyright (C) 1994-1997,2000,2002,2005,2011 Free Software Foundation, Inc.
5 This file is part of the GNU C Library.
6 Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>
7 Some bug fixes by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au>
8 - original wrote n+1 chars in some cases.
9 - stpncpy() ought to behave like strncpy() ie. not null-terminate
10 if limited by n. glibc-1.09 stpncpy() does this.
12 The GNU C Library is free software; you can redistribute it and/or
13 modify it under the terms of the GNU Lesser General Public
14 License as published by the Free Software Foundation; either
15 version 2.1 of the License, or (at your option) any later version.
17 The GNU C Library is distributed in the hope that it will be useful,
18 but WITHOUT ANY WARRANTY; without even the implied warranty of
19 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20 Lesser General Public License for more details.
22 You should have received a copy of the GNU Lesser General Public
23 License along with the GNU C Library; if not, see
24 <http://www.gnu.org/licenses/>. */
27 #include "asm-syntax.h"
31 #define PARMS LINKAGE+4 /* space for 1 saved reg */
33 #define DEST RTN+RTN_SIZE
34 #define SRC DEST+PTR_SIZE
35 #define LEN SRC+PTR_SIZE
38 ENTRY (BP_SYM (__stpncpy))
42 cfi_adjust_cfa_offset (4)
46 cfi_rel_offset (esi, 0)
48 CHECK_BOUNDS_LOW (%eax, DEST(%esp))
49 CHECK_BOUNDS_LOW (%esi, SRC(%esp))
51 subl %eax, %esi /* magic: reduce number of loop variants
52 to one using addressing mode */
53 jmp L(1) /* jump to loop "head" */
57 /* Four times unfolded loop with two loop counters. We get the
58 third value (the source address) by using the index+base
60 L(2): movb (%eax,%esi), %dl /* load current char */
61 movb %dl, (%eax) /* and store it */
62 testb %dl, %dl /* was it NUL? */
63 jz L(7) /* yes, then exit */
65 movb 1(%eax,%esi), %dl /* load current char */
66 movb %dl, 1(%eax) /* and store it */
67 testb %dl, %dl /* was it NUL? */
68 jz L(6) /* yes, then exit */
70 movb 2(%eax,%esi), %dl /* load current char */
71 movb %dl, 2(%eax) /* and store it */
72 testb %dl, %dl /* was it NUL? */
73 jz L(5) /* yes, then exit */
75 movb 3(%eax,%esi), %dl /* load current char */
76 movb %dl, 3(%eax) /* and store it */
77 testb %dl, %dl /* was it NUL? */
78 jz L(4) /* yes, then exit */
80 addl $4, %eax /* increment loop counter for full round */
82 L(1): subl $4, %ecx /* still more than 4 bytes allowed? */
83 jae L(2) /* yes, then go to start of loop */
85 /* The maximal remaining 15 bytes are not processed in a loop. */
87 addl $4, %ecx /* correct above subtraction */
88 jz L(9) /* maximal allowed char reached => go to end */
90 movb (%eax,%esi), %dl /* load current char */
91 movb %dl, (%eax) /* and store it */
92 testb %dl, %dl /* was it NUL? */
93 jz L(3) /* yes, then exit */
95 incl %eax /* increment pointer */
96 decl %ecx /* decrement length counter */
97 jz L(9) /* no more allowed => exit */
99 movb (%eax,%esi), %dl /* load current char */
100 movb %dl, (%eax) /* and store it */
101 testb %dl, %dl /* was it NUL? */
102 jz L(3) /* yes, then exit */
104 incl %eax /* increment pointer */
105 decl %ecx /* decrement length counter */
106 jz L(9) /* no more allowed => exit */
108 movb (%eax,%esi), %dl /* load current char */
109 movb %dl, (%eax) /* and store it */
110 testb %dl, %dl /* was it NUL? */
111 jz L(3) /* yes, then exit */
113 incl %eax /* increment pointer */
114 jmp L(9) /* we don't have to test for counter underflow
115 because we know we had a most 3 bytes
118 /* When coming from the main loop we have to adjust the pointer. */
119 L(4): decl %ecx /* decrement counter */
120 incl %eax /* increment pointer */
122 L(5): decl %ecx /* increment pointer */
123 incl %eax /* increment pointer */
125 L(6): decl %ecx /* increment pointer */
126 incl %eax /* increment pointer */
129 addl $3, %ecx /* correct pre-decrementation of counter
130 at the beginning of the loop; but why 3
131 and not 4? Very simple, we have to count
132 the NUL char we already wrote. */
133 jz L(9) /* counter is also 0 => exit */
135 /* We now have to fill the rest of the buffer with NUL. This
136 is done in a tricky way. Please note that the addressing mode
137 used below is not the same we used above. Here we use the
140 movb $0, (%ecx,%eax) /* store NUL char */
141 L(3): decl %ecx /* all bytes written? */
142 jnz L(8) /* no, then again */
145 #if __BOUNDED_POINTERS__
146 addl %eax, %esi /* undo magic: %esi now points beyond end of SRC */
147 CHECK_BOUNDS_HIGH (%esi, SRC(%esp), jbe)
148 CHECK_BOUNDS_HIGH (%eax, DEST(%esp), jbe)
149 RETURN_BOUNDED_POINTER (DEST(%esp))
151 popl %esi /* restore saved register content */
152 cfi_adjust_cfa_offset (-4)
157 END (BP_SYM (__stpncpy))
159 libc_hidden_def (BP_SYM (__stpncpy))
160 weak_alias (BP_SYM (__stpncpy), BP_SYM (stpncpy))