sdcc/device/lib/malloc.c

   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
  40 typedef struct header HEAPSPACE header_t;
  41
  42 struct 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
  48 header_t *HEAPSPACE __sdcc_heap_free; // First free block, 0 if no free blocks.
  49
  50 extern 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) || defined(__SDCC_mos6502) || defined(__SDCC_mos65c02)
  54
  55 extern 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
  60 extern 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
  65 void __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)
  73 void HEAPSPACE *malloc(size_t size)
  74 #else
  75 void *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) || defined(__SDCC_mos6502) || defined(__SDCC_mos65c02)
  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