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 Lesser General Public License as published by
       7     the Free Software Foundation; either version 2.1, 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 Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser 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  #include <glib.h>
      22  
      23  /* Get size_t.  */
      24  #include <stddef.h>
      25  
      26  /* Get G_MAXSIZE.  */
      27  #include <limits.h>
      28  #if HAVE_STDINT_H
      29  # include <stdint.h>
      30  #endif
      31  
      32  #ifndef _GL_INLINE_HEADER_BEGIN
      33   #error "Please include config.h first."
      34  #endif
      35  _GL_INLINE_HEADER_BEGIN
      36  #ifndef XSIZE_INLINE
      37  # define XSIZE_INLINE _GL_INLINE
      38  #endif
      39  
      40  /* The size of memory objects is often computed through expressions of
      41     type size_t. Example:
      42        void* p = malloc (header_size + n * element_size).
      43     These computations can lead to overflow.  When this happens, malloc()
      44     returns a piece of memory that is way too small, and the program then
      45     crashes while attempting to fill the memory.
      46     To avoid this, the functions and macros in this file check for overflow.
      47     The convention is that G_MAXSIZE represents overflow.
      48     malloc (G_MAXSIZE) is not guaranteed to fail -- think of a malloc
      49     implementation that uses mmap --, it's recommended to use size_overflow_p()
      50     or size_in_bounds_p() before invoking malloc().
      51     The example thus becomes:
      52        size_t size = xsum (header_size, xtimes (n, element_size));
      53        void *p = (size_in_bounds_p (size) ? malloc (size) : NULL);
      54  */
      55  
      56  /* Convert an arbitrary value >= 0 to type size_t.  */
      57  #define xcast_size_t(N) \
      58    ((N) <= G_MAXSIZE ? (size_t) (N) : G_MAXSIZE)
      59  
      60  /* Sum of two sizes, with overflow check.  */
      61  XSIZE_INLINE size_t
      62  #if __GNUC__ >= 3
      63  __attribute__ ((__pure__))
      64  #endif
      65  xsum (size_t size1, size_t size2)
      66  {
      67    size_t sum = size1 + size2;
      68    return (sum >= size1 ? sum : G_MAXSIZE);
      69  }
      70  
      71  /* Sum of three sizes, with overflow check.  */
      72  XSIZE_INLINE size_t
      73  #if __GNUC__ >= 3
      74  __attribute__ ((__pure__))
      75  #endif
      76  xsum3 (size_t size1, size_t size2, size_t size3)
      77  {
      78    return xsum (xsum (size1, size2), size3);
      79  }
      80  
      81  /* Sum of four sizes, with overflow check.  */
      82  XSIZE_INLINE size_t
      83  #if __GNUC__ >= 3
      84  __attribute__ ((__pure__))
      85  #endif
      86  xsum4 (size_t size1, size_t size2, size_t size3, size_t size4)
      87  {
      88    return xsum (xsum (xsum (size1, size2), size3), size4);
      89  }
      90  
      91  /* Maximum of two sizes, with overflow check.  */
      92  XSIZE_INLINE size_t
      93  #if __GNUC__ >= 3
      94  __attribute__ ((__pure__))
      95  #endif
      96  xmax (size_t size1, size_t size2)
      97  {
      98    /* No explicit check is needed here, because for any n:
      99       max (G_MAXSIZE, n) == G_MAXSIZE and max (n, G_MAXSIZE) == G_MAXSIZE.  */
     100    return (size1 >= size2 ? size1 : size2);
     101  }
     102  
     103  /* Multiplication of a count with an element size, with overflow check.
     104     The count must be >= 0 and the element size must be > 0.
     105     This is a macro, not a function, so that it works correctly even
     106     when N is of a wider type and N > G_MAXSIZE.  */
     107  #define xtimes(N, ELSIZE) \
     108    ((N) <= G_MAXSIZE / (ELSIZE) ? (size_t) (N) * (ELSIZE) : G_MAXSIZE)
     109  
     110  /* Check for overflow.  */
     111  #define size_overflow_p(SIZE) \
     112    ((SIZE) == G_MAXSIZE)
     113  /* Check against overflow.  */
     114  #define size_in_bounds_p(SIZE) \
     115    ((SIZE) != G_MAXSIZE)
     116  
     117  _GL_INLINE_HEADER_END
     118  
     119  #endif /* _XSIZE_H */