| 1 | /* Define INTERNAL_SIZE_T, SIZE_SZ, MALLOC_ALIGNMENT and MALLOC_ALIGN_MASK |
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| 2 | for malloc. |
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| 3 | Copyright (C) 2021-2022 Free Software Foundation, Inc. |
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| 4 | This file is part of the GNU C Library. |
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| 5 | |
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| 6 | The GNU C Library is free software; you can redistribute it and/or |
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| 7 | modify it under the terms of the GNU Lesser General Public |
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| 8 | License as published by the Free Software Foundation; either |
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| 9 | version 2.1 of the License, or (at your option) any later version. |
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| 10 | |
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| 11 | The GNU C Library is distributed in the hope that it will be useful, |
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| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 14 | Lesser General Public License for more details. |
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| 15 | |
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| 16 | You should have received a copy of the GNU Lesser General Public |
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| 17 | License along with the GNU C Library; if not, see |
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| 18 | <https://www.gnu.org/licenses/>. */ |
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| 19 | |
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| 20 | #ifndef _GENERIC_MALLOC_SIZE_H |
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| 21 | #define _GENERIC_MALLOC_SIZE_H |
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| 22 | |
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| 23 | /* INTERNAL_SIZE_T is the word-size used for internal bookkeeping of |
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| 24 | chunk sizes. |
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| 25 | |
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| 26 | The default version is the same as size_t. |
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| 27 | |
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| 28 | While not strictly necessary, it is best to define this as an |
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| 29 | unsigned type, even if size_t is a signed type. This may avoid some |
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| 30 | artificial size limitations on some systems. |
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| 31 | |
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| 32 | On a 64-bit machine, you may be able to reduce malloc overhead by |
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| 33 | defining INTERNAL_SIZE_T to be a 32 bit `unsigned int' at the |
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| 34 | expense of not being able to handle more than 2^32 of malloced |
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| 35 | space. If this limitation is acceptable, you are encouraged to set |
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| 36 | this unless you are on a platform requiring 16byte alignments. In |
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| 37 | this case the alignment requirements turn out to negate any |
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| 38 | potential advantages of decreasing size_t word size. |
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| 39 | |
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| 40 | Implementors: Beware of the possible combinations of: |
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| 41 | - INTERNAL_SIZE_T might be signed or unsigned, might be 32 or 64 bits, |
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| 42 | and might be the same width as int or as long |
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| 43 | - size_t might have different width and signedness as INTERNAL_SIZE_T |
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| 44 | - int and long might be 32 or 64 bits, and might be the same width |
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| 45 | |
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| 46 | To deal with this, most comparisons and difference computations |
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| 47 | among INTERNAL_SIZE_Ts should cast them to unsigned long, being |
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| 48 | aware of the fact that casting an unsigned int to a wider long does |
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| 49 | not sign-extend. (This also makes checking for negative numbers |
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| 50 | awkward.) Some of these casts result in harmless compiler warnings |
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| 51 | on some systems. */ |
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| 52 | #ifndef INTERNAL_SIZE_T |
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| 53 | # define INTERNAL_SIZE_T size_t |
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| 54 | #endif |
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| 55 | |
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| 56 | /* The corresponding word size. */ |
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| 57 | #define SIZE_SZ (sizeof (INTERNAL_SIZE_T)) |
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| 58 | |
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| 59 | #include <malloc-alignment.h> |
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| 60 | |
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| 61 | /* The corresponding bit mask value. */ |
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| 62 | #define MALLOC_ALIGN_MASK (MALLOC_ALIGNMENT - 1) |
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| 63 | |
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| 64 | #endif /* _GENERIC_MALLOC_SIZE_H */ |
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| 65 | |
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