gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/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)
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)
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
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