PageRenderTime 21ms CodeModel.GetById 13ms app.highlight 5ms RepoModel.GetById 1ms app.codeStats 0ms

/contrib/cvs/lib/xsize.h

https://bitbucket.org/freebsd/freebsd-head/
C++ Header | 110 lines | 51 code | 12 blank | 47 comment | 2 complexity | 663de01807d5529623f76e1504146462 MD5 | raw file
  1/* xsize.h -- Checked size_t computations.
  2
  3   Copyright (C) 2003 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 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 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, write to the Free Software Foundation,
 17   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
 18
 19#ifndef _XSIZE_H
 20#define _XSIZE_H
 21
 22/* Get size_t.  */
 23#include <stddef.h>
 24
 25/* Get SIZE_MAX.  */
 26#include <limits.h>
 27#if HAVE_INTTYPES_H
 28# include <inttypes.h>
 29#elif HAVE_STDINT_H
 30# include <stdint.h>
 31#endif
 32
 33/* The size of memory objects is often computed through expressions of
 34   type size_t. Example:
 35      void* p = malloc (header_size + n * element_size).
 36   These computations can lead to overflow.  When this happens, malloc()
 37   returns a piece of memory that is way too small, and the program then
 38   crashes while attempting to fill the memory.
 39   To avoid this, the functions and macros in this file check for overflow.
 40   The convention is that SIZE_MAX represents overflow.
 41   malloc (SIZE_MAX) is not guaranteed to fail -- think of a malloc
 42   implementation that uses mmap --, it's recommended to use size_overflow_p()
 43   or size_in_bounds_p() before invoking malloc().
 44   The example thus becomes:
 45      size_t size = xsum (header_size, xtimes (n, element_size));
 46      void *p = (size_in_bounds_p (size) ? malloc (size) : NULL);
 47*/
 48
 49/* Convert an arbitrary value >= 0 to type size_t.  */
 50#define xcast_size_t(N) \
 51  ((N) <= SIZE_MAX ? (size_t) (N) : SIZE_MAX)
 52
 53/* Sum of two sizes, with overflow check.  */
 54static inline size_t
 55#if __GNUC__ >= 3
 56__attribute__ ((__pure__))
 57#endif
 58xsum (size_t size1, size_t size2)
 59{
 60  size_t sum = size1 + size2;
 61  return (sum >= size1 ? sum : SIZE_MAX);
 62}
 63
 64/* Sum of three sizes, with overflow check.  */
 65static inline size_t
 66#if __GNUC__ >= 3
 67__attribute__ ((__pure__))
 68#endif
 69xsum3 (size_t size1, size_t size2, size_t size3)
 70{
 71  return xsum (xsum (size1, size2), size3);
 72}
 73
 74/* Sum of four sizes, with overflow check.  */
 75static inline size_t
 76#if __GNUC__ >= 3
 77__attribute__ ((__pure__))
 78#endif
 79xsum4 (size_t size1, size_t size2, size_t size3, size_t size4)
 80{
 81  return xsum (xsum (xsum (size1, size2), size3), size4);
 82}
 83
 84/* Maximum of two sizes, with overflow check.  */
 85static inline size_t
 86#if __GNUC__ >= 3
 87__attribute__ ((__pure__))
 88#endif
 89xmax (size_t size1, size_t size2)
 90{
 91  /* No explicit check is needed here, because for any n:
 92     max (SIZE_MAX, n) == SIZE_MAX and max (n, SIZE_MAX) == SIZE_MAX.  */
 93  return (size1 >= size2 ? size1 : size2);
 94}
 95
 96/* Multiplication of a count with an element size, with overflow check.
 97   The count must be >= 0 and the element size must be > 0.
 98   This is a macro, not an inline function, so that it works correctly even
 99   when N is of a wider tupe and N > SIZE_MAX.  */
100#define xtimes(N, ELSIZE) \
101  ((N) <= SIZE_MAX / (ELSIZE) ? (size_t) (N) * (ELSIZE) : SIZE_MAX)
102
103/* Check for overflow.  */
104#define size_overflow_p(SIZE) \
105  ((SIZE) == SIZE_MAX)
106/* Check against overflow.  */
107#define size_in_bounds_p(SIZE) \
108  ((SIZE) != SIZE_MAX)
109
110#endif /* _XSIZE_H */