malloc/scratch_buffer_set_array_size.c

   1 /* Variable-sized buffer with on-stack default allocation.
   2    Copyright (C) 2015-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <scratch_buffer.h>
  20 #include <errno.h>
  21 #include <limits.h>
  22
  23 bool
  24 __libc_scratch_buffer_set_array_size (struct scratch_buffer *buffer,
  25                                       size_t nelem, size_t size)
  26 {
  27   size_t new_length = nelem * size;
  28
  29   /* Avoid overflow check if both values are small. */
  30   if ((nelem | size) >> (sizeof (size_t) * CHAR_BIT / 2) != 0
  31       && nelem != 0 && size != new_length / nelem)
  32     {
  33       /* Overflow.  Discard the old buffer, but it must remain valid
  34          to free.  */
  35       scratch_buffer_free (buffer);
  36       scratch_buffer_init (buffer);
  37       __set_errno (ENOMEM);
  38       return false;
  39     }
  40
  41   if (new_length <= buffer->length)
  42     return true;
  43
  44   /* Discard old buffer.  */
  45   scratch_buffer_free (buffer);
  46
  47   char *new_ptr = malloc (new_length);
  48   if (new_ptr == NULL)
  49     {
  50       /* Buffer must remain valid to free.  */
  51       scratch_buffer_init (buffer);
  52       return false;
  53     }
  54
  55   /* Install new heap-based buffer.  */
  56   buffer->data = new_ptr;
  57   buffer->length = new_length;
  58   return true;
  59 }
  60 libc_hidden_def (__libc_scratch_buffer_set_array_size);