root/maint/gnulib/lib/xsize.h

/* */

INCLUDED FROM

DEFINITIONS

1. xsum
2. xsum3
3. xsum4
4. xmax

   1 /* xsize.h -- Checked size_t computations.
   2 
   3    Copyright (C) 2003, 2008-2021 Free Software Foundation, Inc.
   4 
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9 
  10    This file 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 /* 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 /* Get ATTRIBUTE_PURE.  */
  31 #include "attribute.h"
  32 
  33 #ifndef _GL_INLINE_HEADER_BEGIN
  34  #error "Please include config.h first."
  35 #endif
  36 _GL_INLINE_HEADER_BEGIN
  37 #ifndef XSIZE_INLINE
  38 # define XSIZE_INLINE _GL_INLINE
  39 #endif
  40 
  41 /* The size of memory objects is often computed through expressions of
  42    type size_t. Example:
  43       void* p = malloc (header_size + n * element_size).
  44    These computations can lead to overflow.  When this happens, malloc()
  45    returns a piece of memory that is way too small, and the program then
  46    crashes while attempting to fill the memory.
  47    To avoid this, the functions and macros in this file check for overflow.
  48    The convention is that SIZE_MAX represents overflow.
  49    malloc (SIZE_MAX) is not guaranteed to fail -- think of a malloc
  50    implementation that uses mmap --, it's recommended to use size_overflow_p()
  51    or size_in_bounds_p() before invoking malloc().
  52    The example thus becomes:
  53       size_t size = xsum (header_size, xtimes (n, element_size));
  54       void *p = (size_in_bounds_p (size) ? malloc (size) : NULL);
  55 */
  56 
  57 /* Convert an arbitrary value >= 0 to type size_t.  */
  58 #define xcast_size_t(N) \
  59   ((N) <= SIZE_MAX ? (size_t) (N) : SIZE_MAX)
  60 
  61 /* Sum of two sizes, with overflow check.  */
  62 XSIZE_INLINE size_t ATTRIBUTE_PURE
  63 xsum (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.  */
  70 XSIZE_INLINE size_t ATTRIBUTE_PURE
  71 xsum3 (size_t size1, size_t size2, size_t size3)
     /*  */
  72 {
  73   return xsum (xsum (size1, size2), size3);
  74 }
  75 
  76 /* Sum of four sizes, with overflow check.  */
  77 XSIZE_INLINE size_t ATTRIBUTE_PURE
  78 xsum4 (size_t size1, size_t size2, size_t size3, size_t size4)
     /*  */
  79 {
  80   return xsum (xsum (xsum (size1, size2), size3), size4);
  81 }
  82 
  83 /* Maximum of two sizes, with overflow check.  */
  84 XSIZE_INLINE size_t ATTRIBUTE_PURE
  85 xmax (size_t size1, size_t size2)
     /*  */
  86 {
  87   /* No explicit check is needed here, because for any n:
  88      max (SIZE_MAX, n) == SIZE_MAX and max (n, SIZE_MAX) == SIZE_MAX.  */
  89   return (size1 >= size2 ? size1 : size2);
  90 }
  91 
  92 /* Multiplication of a count with an element size, with overflow check.
  93    The count must be >= 0 and the element size must be > 0.
  94    This is a macro, not a function, so that it works correctly even
  95    when N is of a wider type and N > SIZE_MAX.  */
  96 #define xtimes(N, ELSIZE) \
  97   ((N) <= SIZE_MAX / (ELSIZE) ? (size_t) (N) * (ELSIZE) : SIZE_MAX)
  98 
  99 /* Check for overflow.  */
 100 #define size_overflow_p(SIZE) \
 101   ((SIZE) == SIZE_MAX)
 102 /* Check against overflow.  */
 103 #define size_in_bounds_p(SIZE) \
 104   ((SIZE) != SIZE_MAX)
 105 
 106 _GL_INLINE_HEADER_END
 107 
 108 #endif /* _XSIZE_H */

/* */