From 26fd7f11183c629d4b9098e71b6166de2d6b1415 Mon Sep 17 00:00:00 2001
From: seajee <teapods@proton.me>
Date: Thu, 24 Jul 2025 15:38:21 +0200
Subject: [PATCH] Improve modularity, introduce arena_create()

---
 arena.h | 54 +++++++++++++++++++++++++++++++++++++++++-------------
 test.c  |  5 ++---
 2 files changed, 43 insertions(+), 16 deletions(-)

diff --git a/arena.h b/arena.h
index ed551cf..99ce390 100644
--- a/arena.h
+++ b/arena.h
@@ -3,27 +3,42 @@
 
 #include <stddef.h>
 #include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
 
-#ifndef ARENA_MIN_CAPACITY
-#define ARENA_MIN_CAPACITY 4096
-#endif // ARENA_MIN_CAPACITY
+#ifndef ARENA_REGION_CAPACITY
+#    define ARENA_REGION_CAPACITY (8*1024)
+#endif // ARENA_REGION_CAPACITY
+
+#ifndef ARENA_ASSERT
+#    include <assert.h>
+#    define ARENA_ASSERT assert
+#endif // ARENA_ASSERT
+
+#ifndef ARENA_REALLOC
+#    include <stdlib.h>
+#    define ARENA_REALLOC realloc
+#endif // ARENA_REALLOC
+
+#ifndef ARENA_FREE
+#    include <stdlib.h>
+#    define ARENA_FREE free
+#endif // ARENA_FREE
 
 typedef struct Arena_Region Arena_Region;
 
 struct Arena_Region {
+    Arena_Region *next;
     size_t count;
     size_t capacity;
-    Arena_Region *next;
     uint8_t data[];
 };
 
 typedef struct {
     Arena_Region *head;
     Arena_Region *tail;
+    size_t region_capacity;
 } Arena;
 
+Arena arena_create(size_t min_capacity);
 void *arena_alloc(Arena *a, size_t bytes);
 void arena_free(Arena *a);
 void arena_reset(Arena *a);
@@ -32,20 +47,30 @@ void arena_reset(Arena *a);
 
 #ifdef ARENA_IMPLEMENTATION
 
+Arena arena_create(size_t region_capacity)
+{
+    Arena a = {0};
+    a.region_capacity = region_capacity;
+    return a;
+}
+
 void *arena_alloc(Arena *a, size_t bytes)
 {
     if (a == NULL) {
         return NULL;
     }
 
+    size_t region_capacity = (a->region_capacity == 0
+            ? ARENA_REGION_CAPACITY : a->region_capacity);
+
     // Empty arena
     if (a->head == NULL) {
-        size_t size = (bytes > ARENA_MIN_CAPACITY ? bytes : ARENA_MIN_CAPACITY);
-        a->head = (Arena_Region*)malloc(sizeof(*a->head) + size);
+        size_t size = (bytes > region_capacity ? bytes : region_capacity);
+        a->head = (Arena_Region*)ARENA_REALLOC(NULL, sizeof(*a->head) + size);
+        ARENA_ASSERT(a->head != NULL);
         if (a->head == NULL) {
             return NULL;
         }
-        memset(a->head, 0, sizeof(*a->head));
         a->head->count = bytes;
         a->head->capacity = size;
         a->tail = a->head;
@@ -66,14 +91,15 @@ void *arena_alloc(Arena *a, size_t bytes)
         }
 
         // If not create a new region
-        a->tail->next = (Arena_Region*)malloc(sizeof(*a->tail) + bytes);
+        size_t size = (bytes > region_capacity ? bytes : region_capacity);
+        a->tail->next = (Arena_Region*)ARENA_REALLOC(NULL, sizeof(*a->tail) + size);
+        ARENA_ASSERT(a->head != NULL);
         if (a->tail->next == NULL) {
             return NULL;
         }
         a->tail = a->tail->next;
-        memset(a->tail, 0, sizeof(*a->tail));
         a->tail->count = bytes;
-        a->tail->capacity = bytes;
+        a->tail->capacity = size;
         return a->tail->data;
     }
 
@@ -94,7 +120,9 @@ void arena_free(Arena *a)
         cur = next;
     }
 
-    memset(a, 0, sizeof(*a));
+    a->head = NULL;
+    a->tail = NULL;
+    a->region_capacity = 0;
 }
 
 void arena_reset(Arena *a)
diff --git a/test.c b/test.c
index ef4f04d..aac5676 100644
--- a/test.c
+++ b/test.c
@@ -2,13 +2,12 @@
 #include <stdlib.h>
 
 #ifdef DEBUG
-#define malloc(n) (printf("%s:%d:%s: malloc(%ld)\n",\
-            __FILE__, __LINE__, __func__, (n)), malloc((n)));
+#define realloc(p, s) (printf("%s:%d:%s: realloc(%p, %lu)\n",\
+            __FILE__, __LINE__, __func__, (p), (s)), realloc((p), (s)));
 #define free(p)   (printf("%s:%d:%s: free(%p)\n",\
             __FILE__, __LINE__, __func__, (p)), free((p)));
 #endif // DEBUG
 
-#define ARENA_MIN_CAPACITY 400
 #define ARENA_IMPLEMENTATION
 #include "arena.h"