Initial version of arena allocator.

jh_mem.h

@@ -5,7 +5,9 @@ Heavily inspired and designed from:
 * https://github.com/gingerBill/gb/
 
 This is a single header file that contains:
-- allocators
+- Arena allocator
+- Stack allocator (todo)
+- Pool allocator  (todo)
 
 References:
 https://www.gingerbill.org/series/memory-allocation-strategies/
@@ -14,7 +16,7 @@ A implementation of the above with changes were I felt I needed them.
 
 To use this library, do this in *one* C:
 	#define JH_MEM_IMPLEMENTATION
-	#include "jh_io.h"
+	#include "jh_mem.h"
 
 NOTE:
 This is intended to be used with the jh.h header.
@@ -29,6 +31,10 @@ And will require jh.h as it uses the typedefs defined in that file.
 #define DEFAULT_ALIGNMENT (2*sizeof(void *))
 #endif
 
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+
 typedef struct Arena Arena;
 struct Arena {
 	u8      *data;
@@ -37,11 +43,23 @@ struct Arena {
 	usize   curr_offset;
 };
 
-bool is_power_of_two(uptr x);
+u8 is_power_of_two(uptr x);
 uptr align_forward(uptr ptr, usize align);
 void *arena_alloc_align(Arena *a, usize size, usize align);
 void *arena_alloc(Arena *a, usize size);
 
+// Free the allocated arena
+void arena_free(&Arena);
+
+// "clears" the arena by placing the offset to the beggining.
+// Allowing reuse of arena without having to free/alloc.
+void arena_reset(&Arena);
+
+// Initializes an arena instance. 
+// On malloc fail it will return the arena with data as NULL 
+// REQUIRED to arena.data after used
+Arena arena_new(usize arena_init_size);
+
 // -------------------------------------- 
 // -------------------------------------- 
 // implementation Below
@@ -52,7 +70,7 @@ void *arena_alloc(Arena *a, usize size);
 // Arena Functions Start
 // -------------------------------------- 
 
-bool is_power_of_two(uintptr_t x) {
+u8 is_power_of_two(uintptr_t x) {
 	return (x & (x-1)) == 0;
 }
 
@@ -75,17 +93,60 @@ uptr align_forward(uptr ptr, usize align) {
 }
 
 void *arena_alloc_align(Arena *a, usize size, usize align) {
+	// get the pointer
 	uptr current_ptr = (uptr)a->data + (uptr)a->curr_offset;
+
+	// align the offset if needed
 	uptr offset = align_forward(current_ptr, align);
 
-	// Change to relative offset
+	// Change the pointer to relative offset number
 	offset -= (uptr)a->data;
+
+	if (offset+size <= a->data_len) {
+		void *ptr = &a->buf[offset];
+		a->prev_offset = offset;
+		a->curr_offset = offset+size;
+
+		// Zero new memory
+		memset(ptr, 0, size);
+		return ptr;
 	}
 
-void *arena_alloc(Arena *a, size_t size) {
+	// out of memory in arena, handle by doubling arena size;
+	return NULL;
+}
+
+void *arena_alloc(Arena *a, usize size) {
 	return arena_alloc_align(a, size, DEFAULT_ALIGNMENT);
 }
 
+void arena_reset(Arena *arena) {
+	arena->curr_offset = 0;
+	arena->prev_offset = 0;
+}
+
+void arena_free(Arena* arena) {
+    if (arena != NULL && arena->data != NULL) {
+        free(arena->data);
+        arena->data = NULL;
+    }
+}
+
+Arena arena_new(usize arena_init_size) {
+	Arena arena = {0}; 
+	
+	arena.data = (u8 *)malloc(arena_init_size);
+	if(arena.data == NULL) {
+		return arena;
+	}
+
+	arena.data_len = arena_init_size;
+	arena.curr_offset = 0;
+	arena.prev_offset = 0;
+
+	return arena;
+}
+
 // -------------------------------------- 
 // Arena Functions END
 // --------------------------------------