malloc/scratch_buffer_set_array_size.c

   1 /* Variable-sized buffer with on-stack default allocation.
   2    Copyright (C) 2015-2023 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _LIBC
  20 # include <libc-config.h>
  21 #endif
  22
  23 #include <scratch_buffer.h>
  24 #include <errno.h>
  25 #include <limits.h>
  26
  27 bool
  28 __libc_scratch_buffer_set_array_size (struct scratch_buffer *buffer,
  29                                       size_t nelem, size_t size)
  30 {
  31   size_t new_length = nelem * size;
  32
  33   /* Avoid overflow check if both values are small. */
  34   if ((nelem | size) >> (sizeof (size_t) * CHAR_BIT / 2) != 0
  35       && nelem != 0 && size != new_length / nelem)
  36     {
  37       /* Overflow.  Discard the old buffer, but it must remain valid
  38          to free.  */
  39       scratch_buffer_free (buffer);
  40       scratch_buffer_init (buffer);
  41       __set_errno (ENOMEM);
  42       return false;
  43     }
  44
  45   if (new_length <= buffer->length)
  46     return true;
  47
  48   /* Discard old buffer.  */
  49   scratch_buffer_free (buffer);
  50
  51   char *new_ptr = malloc (new_length);
  52   if (new_ptr == NULL)
  53     {
  54       /* Buffer must remain valid to free.  */
  55       scratch_buffer_init (buffer);
  56       return false;
  57     }
  58
  59   /* Install new heap-based buffer.  */
  60   buffer->data = new_ptr;
  61   buffer->length = new_length;
  62   return true;
  63 }
  64 libc_hidden_def (__libc_scratch_buffer_set_array_size)