android / platform / external / e2fsprogs / 1cae2431809b181b214f3f95a54ad6610f46cd65 / . / intl / xsize.h

/* xsize.h -- Checked size_t computations. | |

Copyright (C) 2003 Free Software Foundation, Inc. | |

This program is free software; you can redistribute it and/or modify it | |

under the terms of the GNU Library General Public License as published | |

by the Free Software Foundation; either version 2, 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 | |

Library General Public License for more details. | |

You should have received a copy of the GNU Library General Public | |

License along with this program; if not, write to the Free Software | |

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, | |

USA. */ | |

#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 | |

/* 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. */ | |

static 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. */ | |

static 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. */ | |

static 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. */ | |

static 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 an inline 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) | |

#endif /* _XSIZE_H */ |