1  /* Define INTERNAL_SIZE_T, SIZE_SZ, MALLOC_ALIGNMENT and MALLOC_ALIGN_MASK
       2     for malloc.
       3     Copyright (C) 2021-2023 Free Software Foundation, Inc.
       4     This file is part of the GNU C Library.
       5  
       6     The GNU C Library is free software; you can redistribute it and/or
       7     modify it under the terms of the GNU Lesser General Public
       8     License as published by the Free Software Foundation; either
       9     version 2.1 of the License, or (at your option) any later version.
      10  
      11     The GNU C Library is distributed in the hope that it will be useful,
      12     but WITHOUT ANY WARRANTY; without even the implied warranty of
      13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      14     Lesser General Public License for more details.
      15  
      16     You should have received a copy of the GNU Lesser General Public
      17     License along with the GNU C Library; if not, see
      18     <https://www.gnu.org/licenses/>.  */
      19  
      20  #ifndef _GENERIC_MALLOC_SIZE_H
      21  #define _GENERIC_MALLOC_SIZE_H
      22  
      23  /* INTERNAL_SIZE_T is the word-size used for internal bookkeeping of
      24     chunk sizes.
      25  
      26     The default version is the same as size_t.
      27  
      28     While not strictly necessary, it is best to define this as an
      29     unsigned type, even if size_t is a signed type. This may avoid some
      30     artificial size limitations on some systems.
      31  
      32     On a 64-bit machine, you may be able to reduce malloc overhead by
      33     defining INTERNAL_SIZE_T to be a 32 bit `unsigned int' at the
      34     expense of not being able to handle more than 2^32 of malloced
      35     space. If this limitation is acceptable, you are encouraged to set
      36     this unless you are on a platform requiring 16byte alignments. In
      37     this case the alignment requirements turn out to negate any
      38     potential advantages of decreasing size_t word size.
      39  
      40     Implementors: Beware of the possible combinations of:
      41       - INTERNAL_SIZE_T might be signed or unsigned, might be 32 or 64 bits,
      42         and might be the same width as int or as long
      43       - size_t might have different width and signedness as INTERNAL_SIZE_T
      44       - int and long might be 32 or 64 bits, and might be the same width
      45  
      46     To deal with this, most comparisons and difference computations
      47     among INTERNAL_SIZE_Ts should cast them to unsigned long, being
      48     aware of the fact that casting an unsigned int to a wider long does
      49     not sign-extend. (This also makes checking for negative numbers
      50     awkward.) Some of these casts result in harmless compiler warnings
      51     on some systems.  */
      52  #ifndef INTERNAL_SIZE_T
      53  # define INTERNAL_SIZE_T size_t
      54  #endif
      55  
      56  /* The corresponding word size.  */
      57  #define SIZE_SZ (sizeof (INTERNAL_SIZE_T))
      58  
      59  #include <malloc-alignment.h>
      60  
      61  /* The corresponding bit mask value.  */
      62  #define MALLOC_ALIGN_MASK (MALLOC_ALIGNMENT - 1)
      63  
      64  #endif /* _GENERIC_MALLOC_SIZE_H */