Move everything into a new repo.

1 files changed, 136 insertions, 0 deletions

diff --git a/userland/libc/malloc/oldmalloc.c b/userland/libc/malloc/oldmalloc.c
new file mode 100644
index 0000000..042049d
--- /dev/null
+++ b/userland/libc/malloc/oldmalloc.c
@@ -0,0 +1,136 @@
+#include "stdio.h"
+#include "stdlib.h"
+#include "../errno.h"
+#include <stdint.h>
+#include <stddef.h>
+#include <string.h>
+
+#define NEW_ALLOC_SIZE 0x1000
+
+#define IS_FREE (1 << 0)
+#define IS_FINAL (1 << 1)
+
+typedef struct MallocHeader {
+  uint32_t size;
+  uint8_t flags;
+} MallocHeader;
+
+MallocHeader *head = NULL;
+MallocHeader *final = NULL;
+uint32_t total_heap_size = 0;
+
+int init_heap(void) {
+  head = sbrk(NEW_ALLOC_SIZE);
+  if ((void *)-1 == head) {
+    // perror("sbrk");
+    return 0;
+  }
+  total_heap_size += NEW_ALLOC_SIZE;
+  head->size = NEW_ALLOC_SIZE;
+  head->flags = IS_FREE | IS_FINAL;
+  final = head;
+  return 1;
+}
+
+int add_heap_memory(void) {
+  if ((void *)-1 == sbrk(NEW_ALLOC_SIZE)) {
+    // perror("sbrk");
+    return 0;
+  }
+  total_heap_size += NEW_ALLOC_SIZE;
+  final->size += NEW_ALLOC_SIZE;
+  return 1;
+}
+
+MallocHeader *next_header(MallocHeader *a) {
+  if (a->flags & IS_FINAL)
+    return NULL;
+  return ((void *)a) + a->size;
+}
+
+MallocHeader *find_free_entry(uint32_t s) {
+  // A new header is required as well as the newly allocated chunk
+  s += sizeof(MallocHeader);
+  if (!head)
+    init_heap();
+  MallocHeader *p = head;
+  for (; p; p = next_header(p)) {
+    if (!(p->flags & IS_FREE))
+      continue;
+    if (p->size < s)
+      continue;
+    return p;
+  }
+  return NULL;
+}
+
+void merge_headers(MallocHeader *b) {
+  if (!(b->flags & IS_FREE))
+    return;
+
+  MallocHeader *n = next_header(b);
+  if (!n)
+    return;
+
+  if (!(n->flags & IS_FREE))
+    return;
+
+  // Remove the next header and just increase the newly freed header
+  b->size += n->size;
+  b->flags |= n->flags & IS_FINAL;
+  if (b->flags & IS_FINAL)
+    final = b;
+}
+
+extern int errno;
+// https://pubs.opengroup.org/onlinepubs/9699919799/
+void *malloc(size_t s) {
+  if(s == 0)
+      s = 1;
+
+  MallocHeader *free_entry = find_free_entry(s);
+  if (!free_entry) {
+    if (!add_heap_memory()) {
+        errno = ENOMEM;
+      return NULL;
+    }
+    return malloc(s);
+  }
+
+  // Create a new header
+  MallocHeader *new_entry = ((void *)free_entry) + s;
+  new_entry->flags |= IS_FREE;
+  new_entry->size = free_entry->size - s - sizeof(MallocHeader);
+  new_entry->flags |= free_entry->flags & IS_FINAL;
+  if (new_entry->flags & IS_FINAL)
+    final = new_entry;
+  merge_headers(new_entry);
+
+  // Modify the free entry
+  free_entry->size = s;
+  free_entry->flags = 0;
+
+  return ((void *)free_entry) + sizeof(MallocHeader);
+}
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/
+void *calloc(size_t nelem, size_t elsize) {
+    // The calloc() function shall allocate unused space for an array of
+    // nelem elements each of whose size in bytes is elsize.
+    size_t alloc_size = nelem*elsize;
+    void *rc = malloc(alloc_size);
+    // The space shall be initialized to all bits 0.
+    memset(rc, 0, alloc_size);
+    return rc;
+}
+
+void free(void *p) {
+  // FIXME: This assumes that p is at the start of a allocated area.
+  // Is this a assumption that can be made?
+  MallocHeader *h = p - sizeof(MallocHeader);
+  if (h->flags & IS_FREE)
+    return;
+
+  h->flags |= IS_FREE;
+  merge_headers(h);
+}