| /* xsize.h -- Checked size_t computations. |
| |
| Copyright (C) 2003, 2008-2013 Free Software Foundation, Inc. |
| |
| This program is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 3, or (at your option) |
| any later version. |
| |
| This program is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with this program; if not, see <http://www.gnu.org/licenses/>. */ |
| |
| #ifndef _XSIZE_H |
| #define _XSIZE_H |
| |
| /* Get size_t. */ |
| #include <stddef.h> |
| |
| /* Get SIZE_MAX. */ |
| #include <limits.h> |
| #if HAVE_STDINT_H |
| # include <stdint.h> |
| #endif |
| |
| _GL_INLINE_HEADER_BEGIN |
| #ifndef XSIZE_INLINE |
| # define XSIZE_INLINE _GL_INLINE |
| #endif |
| |
| /* The size of memory objects is often computed through expressions of |
| type size_t. Example: |
| void* p = malloc (header_size + n * element_size). |
| These computations can lead to overflow. When this happens, malloc() |
| returns a piece of memory that is way too small, and the program then |
| crashes while attempting to fill the memory. |
| To avoid this, the functions and macros in this file check for overflow. |
| The convention is that SIZE_MAX represents overflow. |
| malloc (SIZE_MAX) is not guaranteed to fail -- think of a malloc |
| implementation that uses mmap --, it's recommended to use size_overflow_p() |
| or size_in_bounds_p() before invoking malloc(). |
| The example thus becomes: |
| size_t size = xsum (header_size, xtimes (n, element_size)); |
| void *p = (size_in_bounds_p (size) ? malloc (size) : NULL); |
| */ |
| |
| /* Convert an arbitrary value >= 0 to type size_t. */ |
| #define xcast_size_t(N) \ |
| ((N) <= SIZE_MAX ? (size_t) (N) : SIZE_MAX) |
| |
| /* Sum of two sizes, with overflow check. */ |
| XSIZE_INLINE size_t |
| #if __GNUC__ >= 3 |
| __attribute__ ((__pure__)) |
| #endif |
| xsum (size_t size1, size_t size2) |
| { |
| size_t sum = size1 + size2; |
| return (sum >= size1 ? sum : SIZE_MAX); |
| } |
| |
| /* Sum of three sizes, with overflow check. */ |
| XSIZE_INLINE size_t |
| #if __GNUC__ >= 3 |
| __attribute__ ((__pure__)) |
| #endif |
| xsum3 (size_t size1, size_t size2, size_t size3) |
| { |
| return xsum (xsum (size1, size2), size3); |
| } |
| |
| /* Sum of four sizes, with overflow check. */ |
| XSIZE_INLINE size_t |
| #if __GNUC__ >= 3 |
| __attribute__ ((__pure__)) |
| #endif |
| xsum4 (size_t size1, size_t size2, size_t size3, size_t size4) |
| { |
| return xsum (xsum (xsum (size1, size2), size3), size4); |
| } |
| |
| /* Maximum of two sizes, with overflow check. */ |
| XSIZE_INLINE size_t |
| #if __GNUC__ >= 3 |
| __attribute__ ((__pure__)) |
| #endif |
| xmax (size_t size1, size_t size2) |
| { |
| /* No explicit check is needed here, because for any n: |
| max (SIZE_MAX, n) == SIZE_MAX and max (n, SIZE_MAX) == SIZE_MAX. */ |
| return (size1 >= size2 ? size1 : size2); |
| } |
| |
| /* Multiplication of a count with an element size, with overflow check. |
| The count must be >= 0 and the element size must be > 0. |
| This is a macro, not a function, so that it works correctly even |
| when N is of a wider type and N > SIZE_MAX. */ |
| #define xtimes(N, ELSIZE) \ |
| ((N) <= SIZE_MAX / (ELSIZE) ? (size_t) (N) * (ELSIZE) : SIZE_MAX) |
| |
| /* Check for overflow. */ |
| #define size_overflow_p(SIZE) \ |
| ((SIZE) == SIZE_MAX) |
| /* Check against overflow. */ |
| #define size_in_bounds_p(SIZE) \ |
| ((SIZE) != SIZE_MAX) |
| |
| _GL_INLINE_HEADER_END |
| |
| #endif /* _XSIZE_H */ |