1 | /* Define INTERNAL_SIZE_T, SIZE_SZ, MALLOC_ALIGNMENT and MALLOC_ALIGN_MASK |
2 | for malloc. |
3 | Copyright (C) 2021-2024 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 */ |
65 | |