1/* xsize.h -- Checked size_t computations. 2 3 Copyright (C) 2003, 2008-2014 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 <http://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. */ 59XSIZE_INLINE size_t 60#if __GNUC__ >= 3 61__attribute__ ((__pure__)) 62#endif 63xsum (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. */ 70XSIZE_INLINE size_t 71#if __GNUC__ >= 3 72__attribute__ ((__pure__)) 73#endif 74xsum3 (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. */ 80XSIZE_INLINE size_t 81#if __GNUC__ >= 3 82__attribute__ ((__pure__)) 83#endif 84xsum4 (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. */ 90XSIZE_INLINE size_t 91#if __GNUC__ >= 3 92__attribute__ ((__pure__)) 93#endif 94xmax (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