malloc.c (4031B)
1/*------------------------------------------------------------------------- 2 malloc.c - allocate memory. 3 4 Copyright (C) 2015, Philipp Klaus Krause, pkk@spth.de 5 6 This library is free software; you can redistribute it and/or modify it 7 under the terms of the GNU General Public License as published by the 8 Free Software Foundation; either version 2, or (at your option) any 9 later version. 10 11 This 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 14 GNU General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with this library; see the file COPYING. If not, write to the 18 Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston, 19 MA 02110-1301, USA. 20 21 As a special exception, if you link this library with other files, 22 some of which are compiled with SDCC, to produce an executable, 23 this library does not by itself cause the resulting executable to 24 be covered by the GNU General Public License. This exception does 25 not however invalidate any other reasons why the executable file 26 might be covered by the GNU General Public License. 27-------------------------------------------------------------------------*/ 28 29#include <stdlib.h> 30#include <stddef.h> 31 32#if defined(__SDCC_mcs51) || defined(__SDCC_ds390) || defined(__SDCC_ds400) 33#define HEAPSPACE __xdata 34#elif defined(__SDCC_pdk13) || defined(__SDCC_pdk14) || defined(__SDCC_pdk15) 35#define HEAPSPACE __near 36#else 37#define HEAPSPACE 38#endif 39 40typedef struct header HEAPSPACE header_t; 41 42struct header 43{ 44 header_t *next; // Next block. Linked list of all blocks, terminated by pointer to end of heap (or to the byte beyond the end of the heap). 45 header_t *next_free; // Next free block. Used in free blocks only. Overlaps with user data in non-free blocks. Linked list of free blocks, 0-terminated. 46}; 47 48header_t *HEAPSPACE __sdcc_heap_free; // First free block, 0 if no free blocks. 49 50extern header_t __sdcc_heap; 51#define HEAP_START &__sdcc_heap 52 53#if defined(__SDCC_mcs51) || defined(__SDCC_ds390) || defined(__SDCC_ds400) || defined(__SDCC_hc08) || defined(__SDCC_s08) 54 55extern const unsigned int __sdcc_heap_size; 56#define HEAP_END (struct header HEAPSPACE *)((char HEAPSPACE *)&__sdcc_heap + (__sdcc_heap_size - 1)) // -1 To be sure that HEAP_END is bigger than HEAP_START. 57 58#else 59 60extern header_t __sdcc_heap_end; // Just beyond the end of the heap. Must be higher in memory than _sdcc_heap_start. 61#define HEAP_END &__sdcc_heap_end 62 63#endif 64 65void __sdcc_heap_init(void) 66{ 67 __sdcc_heap_free = HEAP_START; 68 __sdcc_heap_free->next = HEAP_END; 69 __sdcc_heap_free->next_free = 0; 70} 71 72#if defined(__SDCC_mcs51) || defined(__SDCC_ds390) || defined(__SDCC_ds400) 73void HEAPSPACE *malloc(size_t size) 74#else 75void *malloc(size_t size) 76#endif 77{ 78 header_t *h; 79 header_t *HEAPSPACE *f; 80 81#if defined(__SDCC_mcs51) || defined(__SDCC_ds390) || defined(__SDCC_ds400) || defined(__SDCC_hc08) || defined(__SDCC_s08) 82 if(!__sdcc_heap_free) 83 __sdcc_heap_init(); 84#endif 85 86 if(!size || size + offsetof(struct header, next_free) < size) 87 return(0); 88 size += offsetof(struct header, next_free); 89 if(size < sizeof(struct header)) // Requiring a minimum size makes it easier to implement free(), and avoid memory leaks. 90 size = sizeof(struct header); 91 92 for(h = __sdcc_heap_free, f = &__sdcc_heap_free; h; f = &(h->next_free), h = h->next_free) 93 { 94 size_t blocksize = (char HEAPSPACE *)(h->next) - (char HEAPSPACE *)h; 95 if(blocksize >= size) // Found free block of sufficient size. 96 { 97 if(blocksize >= size + sizeof(struct header)) // It is worth creating a new free block 98 { 99 header_t *const newheader = (header_t *const)((char HEAPSPACE *)h + size); 100 newheader->next = h->next; 101 newheader->next_free = h->next_free; 102 *f = newheader; 103 h->next = newheader; 104 } 105 else 106 *f = h->next_free; 107 108 return(&(h->next_free)); 109 } 110 } 111 112 return(0); 113} 114