1 files changed, 203 insertions, 0 deletions
diff --git a/lib/arena.c b/lib/arena.c
new file mode 100644
index 0000000..aa2d775
--- /dev/null
+++ b/lib/arena.c
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+/* Copyright (C) 2025 Aryadev Chavali
+
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU General Public License Version 2 for
+ * details.
+
+ * You may distribute and modify this code under the terms of the GNU General
+ * Public License Version 2, which you should have received a copy of along with
+ * this program.  If not, please go to <https://www.gnu.org/licenses/>.
+
+ * Created: 2025-04-05
+ * Description: Implementations for memory models.
+ */
+
+#include <lib/arena.h>
+
+#include <malloc.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+page_t *page_create(u64 size)
+{
+  size           = MAX(size, PAGE_DEFAULT_SIZE);
+  page_t *page   = calloc(1, sizeof(*page) + size);
+  page->next     = NULL;
+  page->size     = 0;
+  page->capacity = size;
+  return page;
+}
+
+void page_resize(page_t **page, u64 size)
+{
+  if (!page)
+    return;
+  else if (!(*page))
+    *page = page_create(size);
+  else if (page[0]->capacity < size)
+  {
+    page[0]->capacity = MAX(size, page[0]->capacity * 1.5);
+    page[0]           = realloc(page[0], sizeof(*page[0]) + page[0]->capacity);
+  }
+}
+
+i64 page_append(page_t *page, void *data, u64 size)
+{
+  if (!page || page->size + size >= page->capacity)
+    return -1;
+  if (data)
+    memcpy(page->data + page->size, data, size);
+  u64 ptr = page->size;
+  page->size += size;
+  return ptr;
+}
+
+u64 page_rappend(page_t **page, void *data, u64 size)
+{
+  page_resize(page, page[0]->size + size);
+  if (data)
+    memcpy(page[0]->data + page[0]->size, data, size);
+  u64 ptr = page[0]->size;
+  page[0]->size += size;
+  return ptr;
+}
+
+void *arena_alloc(arena_t *arena, u64 size)
+{
+  if (!arena)
+    return NULL;
+  else if (!arena->start)
+  {
+    arena->start = page_create(1);
+    arena->end   = arena->start;
+  }
+
+  page_t *best_fit;
+  for (best_fit = arena->start; best_fit; best_fit = best_fit->next)
+    if (best_fit->size + size + MEMORY_ALIGNMENT < best_fit->capacity)
+      break;
+
+  if (!best_fit)
+  {
+    best_fit         = page_create(size);
+    arena->end->next = best_fit;
+    arena->end       = best_fit;
+  }
+
+  // NOTE: Fsanitize has a hissy fit if we don't align memory "correctly"
+  u64 offset = 0;
+
+  if (size % MEMORY_ALIGNMENT == 0)
+  {
+    u64 div = (((u64)(best_fit->data + best_fit->size)) % MEMORY_ALIGNMENT);
+    if (div != 0)
+      offset = MEMORY_ALIGNMENT - div;
+  }
+
+  void *start = best_fit->data + best_fit->size + offset;
+
+  best_fit->size += size + offset;
+
+  return start;
+}
+
+void *arena_realloc(arena_t *arena, void *ptr, u64 oldsize, u64 newsize)
+{
+  if (!ptr)
+    return arena_alloc(arena, newsize);
+  else if (!arena || !arena->start)
+    return NULL;
+  else if (newsize <= oldsize)
+    // No need to change anything.
+    return ptr;
+
+  bool copy_into_new = true;
+  void *start        = NULL;
+  page_t *old_page = NULL, *best_fit = NULL;
+
+  for (page_t *page = arena->start; page; page = page->next)
+  {
+    if (!best_fit && page->size + newsize < page->capacity)
+      best_fit = page;
+    if (page->data <= (u8 *)ptr &&
+        (u8 *)(ptr) + oldsize <= page->data + page->capacity)
+      old_page = page;
+  }
+
+  // If the old page exists, ptr is the latest allocation in it, and it has
+  // enough space to contain the new size, just resize and return.
+  if (old_page && old_page->data + old_page->size - oldsize == ptr &&
+      old_page->size - oldsize + newsize < old_page->capacity)
+  {
+    start = ptr;
+    old_page->size += newsize - oldsize;
+    copy_into_new = false;
+  }
+  else
+  {
+    if (!old_page)
+      copy_into_new = false;
+    if (!best_fit)
+    {
+      best_fit         = page_create(newsize);
+      arena->end->next = best_fit;
+      arena->end       = best_fit;
+    }
+
+    start = best_fit->data + best_fit->size;
+    best_fit->size += newsize;
+  }
+
+  if (copy_into_new)
+  {
+    memcpy(start, ptr, oldsize);
+    memset(start + oldsize, 0, newsize - oldsize);
+  }
+
+  return start;
+}
+
+void arena_attach(arena_t *arena, page_t *page)
+{
+  if (!arena || !page)
+    return;
+  else if (!arena->start || !arena->end)
+  {
+    arena->start = page;
+    arena->end   = page;
+  }
+  else
+  {
+    page->next   = arena->start;
+    arena->start = page;
+  }
+}
+
+void arena_reset(arena_t *arena)
+{
+  if (!arena || !arena->start)
+    return;
+
+  for (page_t *cur = arena->start; cur; cur = cur->next)
+  {
+    if (cur->size == 0)
+      continue;
+    cur->size = 0;
+    memset(cur->data, 0, cur->capacity);
+  }
+}
+
+void arena_cleanup(arena_t *arena)
+{
+  if (!arena || !arena->start)
+    return;
+
+  for (page_t *cur = arena->start, *next = NULL; cur;
+       next = cur->next, free(cur), cur = next)
+    continue;
+
+  memset(arena, 0, sizeof(*arena));
+}