1 /* Variable-sized buffer with on-stack default allocation.
2 Copyright (C) 2017-2023 Free Software Foundation, Inc.
3
4 This file is free software: you can redistribute it and/or modify
5 it under the terms of the GNU Lesser General Public License as
6 published by the Free Software Foundation; either version 2.1 of the
7 License, or (at your option) any later version.
8
9 This file is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public License
15 along with this program. If not, see <https://www.gnu.org/licenses/>. */
16
17 /* Written by Paul Eggert, 2017. */
18
19 #ifndef _GL_SCRATCH_BUFFER_H
20 #define _GL_SCRATCH_BUFFER_H
21
22 /* Scratch buffers with a default stack allocation and fallback to
23 heap allocation. It is expected that this function is used in this
24 way:
25
26 struct scratch_buffer tmpbuf;
27 scratch_buffer_init (&tmpbuf);
28
29 while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length))
30 if (!scratch_buffer_grow (&tmpbuf))
31 return -1;
32
33 scratch_buffer_free (&tmpbuf);
34 return 0;
35
36 The allocation functions (scratch_buffer_grow,
37 scratch_buffer_grow_preserve, scratch_buffer_set_array_size) make
38 sure that the heap allocation, if any, is freed, so that the code
39 above does not have a memory leak. The buffer still remains in a
40 state that can be deallocated using scratch_buffer_free, so a loop
41 like this is valid as well:
42
43 struct scratch_buffer tmpbuf;
44 scratch_buffer_init (&tmpbuf);
45
46 while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length))
47 if (!scratch_buffer_grow (&tmpbuf))
48 break;
49
50 scratch_buffer_free (&tmpbuf);
51
52 scratch_buffer_grow and scratch_buffer_grow_preserve are guaranteed
53 to grow the buffer by at least 512 bytes. This means that when
54 using the scratch buffer as a backing store for a non-character
55 array whose element size, in bytes, is 512 or smaller, the scratch
56 buffer only has to grow once to make room for at least one more
57 element.
58 */
59
60 /* Scratch buffer. Must be initialized with scratch_buffer_init
61 before its use. */
62 struct scratch_buffer;
63
64 /* Initializes *BUFFER so that BUFFER->data points to BUFFER->__space
65 and BUFFER->length reflects the available space. */
66 #if 0
67 extern void scratch_buffer_init (struct scratch_buffer *buffer);
68 #endif
69
70 /* Deallocates *BUFFER (if it was heap-allocated). */
71 #if 0
72 extern void scratch_buffer_free (struct scratch_buffer *buffer);
73 #endif
74
75 /* Grow *BUFFER by some arbitrary amount. The buffer contents is NOT
76 preserved. Return true on success, false on allocation failure (in
77 which case the old buffer is freed). On success, the new buffer is
78 larger than the previous size. On failure, *BUFFER is deallocated,
79 but remains in a free-able state, and errno is set. */
80 #if 0
81 extern bool scratch_buffer_grow (struct scratch_buffer *buffer);
82 #endif
83
84 /* Like scratch_buffer_grow, but preserve the old buffer
85 contents on success, as a prefix of the new buffer. */
86 #if 0
87 extern bool scratch_buffer_grow_preserve (struct scratch_buffer *buffer);
88 #endif
89
90 /* Grow *BUFFER so that it can store at least NELEM elements of SIZE
91 bytes. The buffer contents are NOT preserved. Both NELEM and SIZE
92 can be zero. Return true on success, false on allocation failure
93 (in which case the old buffer is freed, but *BUFFER remains in a
94 free-able state, and errno is set). It is unspecified whether this
95 function can reduce the array size. */
96 #if 0
97 extern bool scratch_buffer_set_array_size (struct scratch_buffer *buffer,
98 size_t nelem, size_t size);
99 #endif
100
101
102 /* The implementation is imported from glibc. */
103
104 /* Avoid possible conflicts with symbols exported by the GNU libc. */
105 #define __libc_scratch_buffer_grow gl_scratch_buffer_grow
106 #define __libc_scratch_buffer_grow_preserve gl_scratch_buffer_grow_preserve
107 #define __libc_scratch_buffer_set_array_size gl_scratch_buffer_set_array_size
108
109 #ifndef _GL_LIKELY
110 /* Rely on __builtin_expect, as provided by the module 'builtin-expect'. */
111 # define _GL_LIKELY(cond) __builtin_expect ((cond), 1)
112 # define _GL_UNLIKELY(cond) __builtin_expect ((cond), 0)
113 #endif
114
115 #include <malloc/scratch_buffer.gl.h>
116
117 #endif /* _GL_SCRATCH_BUFFER_H */