aboutsummaryrefslogtreecommitdiffstats
path: root/dos/malloc.c
blob: 2d74459cce4b5befd1af61033aa03db0c7809525 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
/*
 * malloc.c
 *
 * Very simple linked-list based malloc()/free().
 */

#include <stdlib.h>
#include <string.h>
#include "malloc.h"

struct free_arena_header __malloc_head =
{
  {
    ARENA_TYPE_HEAD,
    0,
    &__malloc_head,
    &__malloc_head,
  },
  &__malloc_head,
  &__malloc_head
};

extern void *__mem_end;		/* In argv.c */

void __init_memory_arena(void)
{
  extern char __heap_end[];
  struct free_arena_header *fp;

  fp = (struct free_arena_header *)__mem_end;
  fp->a.type = ARENA_TYPE_FREE;
  fp->a.size = __heap_end - (char *)__mem_end;

  /* Insert into chains */
  fp->a.next = fp->a.prev = &__malloc_head;
  fp->next_free = fp->prev_free = &__malloc_head;
  __malloc_head.a.next = __malloc_head.a.prev = fp;
  __malloc_head.next_free = __malloc_head.prev_free = fp;
}

static void *__malloc_from_block(struct free_arena_header *fp, size_t size)
{
  size_t fsize;
  struct free_arena_header *nfp, *na;

  fsize = fp->a.size;

  /* We need the 2* to account for the larger requirements of a free block */
  if ( fsize >= size+2*sizeof(struct arena_header) ) {
    /* Bigger block than required -- split block */
    nfp = (struct free_arena_header *)((char *)fp + size);
    na = fp->a.next;

    nfp->a.type = ARENA_TYPE_FREE;
    nfp->a.size = fsize-size;
    fp->a.type  = ARENA_TYPE_USED;
    fp->a.size  = size;

    /* Insert into all-block chain */
    nfp->a.prev = fp;
    nfp->a.next = na;
    na->a.prev = nfp;
    fp->a.next = nfp;

    /* Replace current block on free chain */
    nfp->next_free = fp->next_free;
    nfp->prev_free = fp->prev_free;
    fp->next_free->prev_free = nfp;
    fp->prev_free->next_free = nfp;
  } else {
    /* Allocate the whole block */
    fp->a.type = ARENA_TYPE_USED;

    /* Remove from free chain */
    fp->next_free->prev_free = fp->prev_free;
    fp->prev_free->next_free = fp->next_free;
  }

  return (void *)(&fp->a + 1);
}

void *malloc(size_t size)
{
  struct free_arena_header *fp;

  if ( size == 0 )
    return NULL;

  /* Add the obligatory arena header, and round up */
  size = (size+2*sizeof(struct arena_header)-1) & ~ARENA_SIZE_MASK;

  for ( fp = __malloc_head.next_free ; fp->a.type != ARENA_TYPE_HEAD ;
	fp = fp->next_free ) {
    if ( fp->a.size >= size ) {
      /* Found fit -- allocate out of this block */
      return __malloc_from_block(fp, size);
    }
  }

  /* Nothing found... need to request a block from the kernel */
  return NULL;			/* No kernel to get stuff from */
}

void *calloc(size_t nmemb, size_t size)
{
  void *p;
  size *= nmemb;
  p = malloc(size);
  if (p)
    memset(p, 0, size);
  return p;
}