1 /* Define INTERNAL_SIZE_T, SIZE_SZ, MALLOC_ALIGNMENT and MALLOC_ALIGN_MASK 2 for malloc. 3 Copyright (C) 2021-2022 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