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1 | /* xsize.h -- Checked size_t computations. |
2 | ||
5e69ceb7 | 3 | Copyright (C) 2003, 2008-2014 Free Software Foundation, Inc. |
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4 | |
5 | This program is free software; you can redistribute it and/or modify | |
6 | it under the terms of the GNU Lesser General Public License as published by | |
7 | the Free Software Foundation; either version 2, 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 Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public License | |
005de2e8 | 16 | along with this program; if not, see <http://www.gnu.org/licenses/>. */ |
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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 | ||
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30 | #ifndef _GL_INLINE_HEADER_BEGIN |
31 | #error "Please include config.h first." | |
32 | #endif | |
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33 | _GL_INLINE_HEADER_BEGIN |
34 | #ifndef XSIZE_INLINE | |
35 | # define XSIZE_INLINE _GL_INLINE | |
36 | #endif | |
37 | ||
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38 | /* The size of memory objects is often computed through expressions of |
39 | type size_t. Example: | |
40 | void* p = malloc (header_size + n * element_size). | |
41 | These computations can lead to overflow. When this happens, malloc() | |
42 | returns a piece of memory that is way too small, and the program then | |
43 | crashes while attempting to fill the memory. | |
44 | To avoid this, the functions and macros in this file check for overflow. | |
45 | The convention is that SIZE_MAX represents overflow. | |
46 | malloc (SIZE_MAX) is not guaranteed to fail -- think of a malloc | |
47 | implementation that uses mmap --, it's recommended to use size_overflow_p() | |
48 | or size_in_bounds_p() before invoking malloc(). | |
49 | The example thus becomes: | |
50 | size_t size = xsum (header_size, xtimes (n, element_size)); | |
51 | void *p = (size_in_bounds_p (size) ? malloc (size) : NULL); | |
52 | */ | |
53 | ||
54 | /* Convert an arbitrary value >= 0 to type size_t. */ | |
55 | #define xcast_size_t(N) \ | |
56 | ((N) <= SIZE_MAX ? (size_t) (N) : SIZE_MAX) | |
57 | ||
58 | /* Sum of two sizes, with overflow check. */ | |
7ae4e75a | 59 | XSIZE_INLINE size_t |
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60 | #if __GNUC__ >= 3 |
61 | __attribute__ ((__pure__)) | |
62 | #endif | |
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. */ | |
7ae4e75a | 70 | XSIZE_INLINE size_t |
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71 | #if __GNUC__ >= 3 |
72 | __attribute__ ((__pure__)) | |
73 | #endif | |
74 | xsum3 (size_t size1, size_t size2, size_t size3) | |
75 | { | |
76 | return xsum (xsum (size1, size2), size3); | |
77 | } | |
78 | ||
79 | /* Sum of four sizes, with overflow check. */ | |
7ae4e75a | 80 | XSIZE_INLINE size_t |
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81 | #if __GNUC__ >= 3 |
82 | __attribute__ ((__pure__)) | |
83 | #endif | |
84 | xsum4 (size_t size1, size_t size2, size_t size3, size_t size4) | |
85 | { | |
86 | return xsum (xsum (xsum (size1, size2), size3), size4); | |
87 | } | |
88 | ||
89 | /* Maximum of two sizes, with overflow check. */ | |
7ae4e75a | 90 | XSIZE_INLINE size_t |
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91 | #if __GNUC__ >= 3 |
92 | __attribute__ ((__pure__)) | |
93 | #endif | |
94 | xmax (size_t size1, size_t size2) | |
95 | { | |
96 | /* No explicit check is needed here, because for any n: | |
97 | max (SIZE_MAX, n) == SIZE_MAX and max (n, SIZE_MAX) == SIZE_MAX. */ | |
98 | return (size1 >= size2 ? size1 : size2); | |
99 | } | |
100 | ||
101 | /* Multiplication of a count with an element size, with overflow check. | |
102 | The count must be >= 0 and the element size must be > 0. | |
7ae4e75a | 103 | This is a macro, not a function, so that it works correctly even |
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104 | when N is of a wider type and N > SIZE_MAX. */ |
105 | #define xtimes(N, ELSIZE) \ | |
106 | ((N) <= SIZE_MAX / (ELSIZE) ? (size_t) (N) * (ELSIZE) : SIZE_MAX) | |
107 | ||
108 | /* Check for overflow. */ | |
109 | #define size_overflow_p(SIZE) \ | |
110 | ((SIZE) == SIZE_MAX) | |
111 | /* Check against overflow. */ | |
112 | #define size_in_bounds_p(SIZE) \ | |
113 | ((SIZE) != SIZE_MAX) | |
114 | ||
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115 | _GL_INLINE_HEADER_END |
116 | ||
c4b681fd | 117 | #endif /* _XSIZE_H */ |