sdcc/device/lib/realloc.c

   1 /*-------------------------------------------------------------------------
   2    realloc.c - allocate memory.
   3
   4    Always behaves according to C90 (i.e. does not take advantage of
   5    undefined behaviour introduced in C2X or implementation-defined
   6    behaviour introduced in C17.
   7
   8    Copyright (C) 2015-2020, Philipp Klaus Krause, pkk@spth.de
   9
  10    This library is free software; you can redistribute it and/or modify it
  11    under the terms of the GNU General Public License as published by the
  12    Free Software Foundation; either version 2, or (at your option) any
  13    later version.
  14
  15    This library is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with this library; see the file COPYING. If not, write to the
  22    Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
  23    MA 02110-1301, USA.
  24
  25    As a special exception, if you link this library with other files,
  26    some of which are compiled with SDCC, to produce an executable,
  27    this library does not by itself cause the resulting executable to
  28    be covered by the GNU General Public License. This exception does
  29    not however invalidate any other reasons why the executable file
  30    might be covered by the GNU General Public License.
  31 -------------------------------------------------------------------------*/
  32
  33 #include <stdlib.h>
  34 #include <stddef.h>
  35 #include <string.h>
  36
  37 #if defined(__SDCC_mcs51) || defined(__SDCC_ds390) || defined(__SDCC_ds400)
  38 #define HEAPSPACE __xdata
  39 #elif defined(__SDCC_pdk13) || defined(__SDCC_pdk14) || defined(__SDCC_pdk15)
  40 #define HEAPSPACE __near
  41 #else
  42 #define HEAPSPACE
  43 #endif
  44
  45 typedef struct header HEAPSPACE header_t;
  46
  47 struct header
  48 {
  49         header_t *next;
  50         header_t *next_free;
  51 };
  52
  53 extern header_t *HEAPSPACE __sdcc_heap_free;
  54
  55 void __sdcc_heap_init(void);
  56
  57 #if defined(__SDCC_mcs51) || defined(__SDCC_ds390) || defined(__SDCC_ds400)
  58 void HEAPSPACE *realloc(void *ptr, size_t size)
  59 #else
  60 void *realloc(void *ptr, size_t size)
  61 #endif
  62 {
  63         void HEAPSPACE *ret;
  64         header_t *h, *next_free, *prev_free;
  65         header_t *HEAPSPACE *f, *HEAPSPACE *pf;
  66         size_t blocksize, oldblocksize, maxblocksize;
  67
  68 #if defined(__SDCC_mcs51) || defined(__SDCC_ds390) || defined(__SDCC_ds400) || defined(__SDCC_hc08) || defined(__SDCC_s08)
  69         if(!__sdcc_heap_free)
  70                 __sdcc_heap_init();
  71 #endif
  72
  73         if(!ptr)
  74                 return(malloc(size));
  75
  76         if(!size)
  77         {
  78                 free(ptr);
  79                 return(0);
  80         }
  81
  82         prev_free = 0, pf = 0;
  83         for(h = __sdcc_heap_free, f = &__sdcc_heap_free; h && h < ptr; prev_free = h, pf = f, f = &(h->next_free), h = h->next_free); // Find adjacent blocks in free list
  84         next_free = h;
  85
  86         if(size + offsetof(struct header, next_free) < size) // Handle overflow
  87                 return(0);
  88         blocksize = size + offsetof(struct header, next_free);
  89         if(blocksize < sizeof(struct header)) // Requiring a minimum size makes it easier to implement free(), and avoid memory leaks.
  90                 blocksize = sizeof(struct header);
  91
  92         h = (void HEAPSPACE *)((char HEAPSPACE *)(ptr) - offsetof(struct header, next_free));
  93         oldblocksize = (char HEAPSPACE *)(h->next) - (char HEAPSPACE *)h;
  94
  95         maxblocksize = oldblocksize;
  96         if(prev_free && prev_free->next == h) // Can merge with previous block
  97                 maxblocksize += (char HEAPSPACE *)h - (char HEAPSPACE *)prev_free;
  98         if(next_free == h->next) // Can merge with next block
  99                 maxblocksize += (char HEAPSPACE *)(next_free->next) - (char HEAPSPACE *)next_free;
 100
 101         if(blocksize <= maxblocksize) // Can resize in place.
 102         {
 103                 if(prev_free && prev_free->next == h) // Always move into previous block to defragment
 104                 {
 105                         memmove(prev_free, h, blocksize <= oldblocksize ? blocksize : oldblocksize);
 106                         h = prev_free;
 107                         *pf = next_free;
 108                         f = pf;
 109                 }
 110
 111                 if(next_free && next_free == h->next) // Merge with following block
 112                 {
 113                         h->next = next_free->next;
 114                         *f = next_free->next_free;
 115                 }
 116
 117                 if(maxblocksize >= blocksize + sizeof(struct header)) // Create new block from free space
 118                 {
 119                         header_t *const newheader = (header_t *const)((char HEAPSPACE *)h + blocksize);
 120                         newheader->next = h->next;
 121                         newheader->next_free = *f;
 122                         *f = newheader;
 123                         h->next = newheader;
 124                 }
 125
 126                 return(&(h->next_free));
 127         }
 128
 129         if(ret = malloc(size))
 130         {
 131                 size_t oldsize = oldblocksize - offsetof(struct header, next_free);
 132                 memcpy(ret, ptr, size <= oldsize ? size : oldsize);
 133                 free(ptr);
 134                 return(ret);
 135         }
 136
 137         return(0);
 138 }
 139