gsasl  1.10.0
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xsize.h
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1 /* xsize.h -- Checked size_t computations.
2 
3  Copyright (C) 2003, 2008-2021 Free Software Foundation, Inc.
4 
5  This program is free software; you can redistribute it and/or modify
6  it under the terms of the GNU General Public License as published by
7  the Free Software Foundation; either version 3, or (at your option)
8  any later version.
9 
10  This program is distributed in the hope that it will be useful,
11  but WITHOUT ANY WARRANTY; without even the implied warranty of
12  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13  GNU General Public License for more details.
14 
15  You should have received a copy of the GNU General Public License
16  along with this program; if not, see <https://www.gnu.org/licenses/>. */
17 
18 #ifndef _XSIZE_H
19 #define _XSIZE_H
20 
21 /* Get size_t. */
22 #include <stddef.h>
23 
24 /* Get SIZE_MAX. */
25 #include <limits.h>
26 #if HAVE_STDINT_H
27 # include <stdint.h>
28 #endif
29 
30 /* Get ATTRIBUTE_PURE. */
31 #include "attribute.h"
32 
33 #ifndef _GL_INLINE_HEADER_BEGIN
34  #error "Please include config.h first."
35 #endif
36 _GL_INLINE_HEADER_BEGIN
37 #ifndef XSIZE_INLINE
38 # define XSIZE_INLINE _GL_INLINE
39 #endif
40 
41 /* The size of memory objects is often computed through expressions of
42  type size_t. Example:
43  void* p = malloc (header_size + n * element_size).
44  These computations can lead to overflow. When this happens, malloc()
45  returns a piece of memory that is way too small, and the program then
46  crashes while attempting to fill the memory.
47  To avoid this, the functions and macros in this file check for overflow.
48  The convention is that SIZE_MAX represents overflow.
49  malloc (SIZE_MAX) is not guaranteed to fail -- think of a malloc
50  implementation that uses mmap --, it's recommended to use size_overflow_p()
51  or size_in_bounds_p() before invoking malloc().
52  The example thus becomes:
53  size_t size = xsum (header_size, xtimes (n, element_size));
54  void *p = (size_in_bounds_p (size) ? malloc (size) : NULL);
55 */
56 
57 /* Convert an arbitrary value >= 0 to type size_t. */
58 #define xcast_size_t(N) \
59  ((N) <= SIZE_MAX ? (size_t) (N) : SIZE_MAX)
60 
61 /* Sum of two sizes, with overflow check. */
63 xsum (size_t size1, size_t size2)
64 {
65  size_t sum = size1 + size2;
66  return (sum >= size1 ? sum : SIZE_MAX);
67 }
68 
69 /* Sum of three sizes, with overflow check. */
71 xsum3 (size_t size1, size_t size2, size_t size3)
72 {
73  return xsum (xsum (size1, size2), size3);
74 }
75 
76 /* Sum of four sizes, with overflow check. */
78 xsum4 (size_t size1, size_t size2, size_t size3, size_t size4)
79 {
80  return xsum (xsum (xsum (size1, size2), size3), size4);
81 }
82 
83 /* Maximum of two sizes, with overflow check. */
85 xmax (size_t size1, size_t size2)
86 {
87  /* No explicit check is needed here, because for any n:
88  max (SIZE_MAX, n) == SIZE_MAX and max (n, SIZE_MAX) == SIZE_MAX. */
89  return (size1 >= size2 ? size1 : size2);
90 }
91 
92 /* Multiplication of a count with an element size, with overflow check.
93  The count must be >= 0 and the element size must be > 0.
94  This is a macro, not a function, so that it works correctly even
95  when N is of a wider type and N > SIZE_MAX. */
96 #define xtimes(N, ELSIZE) \
97  ((N) <= SIZE_MAX / (ELSIZE) ? (size_t) (N) * (ELSIZE) : SIZE_MAX)
98 
99 /* Check for overflow. */
100 #define size_overflow_p(SIZE) \
101  ((SIZE) == SIZE_MAX)
102 /* Check against overflow. */
103 #define size_in_bounds_p(SIZE) \
104  ((SIZE) != SIZE_MAX)
105 
106 _GL_INLINE_HEADER_END
107 
108 #endif /* _XSIZE_H */
#define ATTRIBUTE_PURE
Definition: attribute.h:187
#define XSIZE_INLINE
Definition: xsize.h:38
_GL_INLINE size_t _GL_ATTRIBUTE_PURE xsum(size_t size1, size_t size2)
Definition: xsize.h:63
_GL_INLINE size_t _GL_ATTRIBUTE_PURE xsum3(size_t size1, size_t size2, size_t size3)
Definition: xsize.h:71
_GL_INLINE size_t _GL_ATTRIBUTE_PURE xmax(size_t size1, size_t size2)
Definition: xsize.h:85
_GL_INLINE size_t _GL_ATTRIBUTE_PURE xsum4(size_t size1, size_t size2, size_t size3, size_t size4)
Definition: xsize.h:78
#define SIZE_MAX
Definition: quotearg.c:53