1 | /* xsize.h -- Checked size_t computations. |
2 | |
3 | Copyright (C) 2003, 2008-2019 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 | #ifndef _GL_INLINE_HEADER_BEGIN |
31 | #error "Please include config.h first." |
32 | #endif |
33 | _GL_INLINE_HEADER_BEGIN |
34 | #ifndef XSIZE_INLINE |
35 | # define XSIZE_INLINE _GL_INLINE |
36 | #endif |
37 | |
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. */ |
59 | XSIZE_INLINE size_t |
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. */ |
70 | XSIZE_INLINE size_t |
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. */ |
80 | XSIZE_INLINE size_t |
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. */ |
90 | XSIZE_INLINE size_t |
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. |
103 | This is a macro, not a function, so that it works correctly even |
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 | |
115 | _GL_INLINE_HEADER_END |
116 | |
117 | #endif /* _XSIZE_H */ |
118 | |