WIP

arena_allocator.c

@@ -1,8 +1,48 @@
 #include "cig.h"
+#include <stdbool.h>
+
+static void arena_reset(arena_allocator_t *this) {
+	if (0 < this->bytes_outside_data) {
+		this->capacity += this->bytes_outside_data;
+		this->bytes_outside_data = 0;
+		allocator_reset(this->allocator);
+		this->data = NULL;
+	}
+	if (this->data == NULL) {
+		this->data = allocator_alloc(this->allocator, this->capacity);
+	}
+	this->size = 0;
+}
 
 static void *arena_alloc(arena_allocator_t *this, size_t bytes) {
-	
+	// Assume that the this->size index already points to an address that is
+	// divisible by MAX_ALIGN. The following is a magic formula from the GPT
+	// gods that rounds up bytes to a multiple of MAX_ALIGN.
+	// TODO: write tests that assert that this formula is always correct.
+	bytes = (bytes + MAX_ALIGN - 1) / MAX_ALIGN * MAX_ALIGN;
+	size_t remaining = this->capacity - this->size;
+	if (remaining < bytes) {
+		this->bytes_outside_data += bytes;
+		return allocator_alloc(this->allocator, bytes);
 	}
+	void *ptr = &this->data[this->size];
+	this->size += bytes;
+	return ptr;
+}
+
+static void *arena_resize(arena_allocator_t *this, void *old_ptr, size_t bytes) {
+	bool is_old_ptr_in_data = this->data <= old_ptr && old_ptr < &this->data[this->size]
+	// TODO: implement this
+}
+
+// typedef struct arena_allocator {
+// 	allocator_t allocator;
+// 	size_t size;
+// 	size_t capacity;
+// 	size_t bytes_outside_data;
+// 	uint8_t *data;
+// } arena_allocator_t;
+
 
 allocator_t allocator_from_arena(arena_allocator_t *this) {
 }

cig.h

@@ -6,7 +6,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-typedef union any_align { char c; int i; long l; long long ll; float f; double d; void *p; } any_align_t;
+typedef union any_align { char c; int i; long l; long long ll; float f; double d; void *p; long double ld; } any_align_t;
 #define MAX_ALIGN ((size_t) sizeof(any_align_t))
 #define KB (1024)
 #define MB (KB * KB)
@@ -14,7 +14,6 @@ typedef union any_align { char c; int i; long l; long long ll; float f; double d
 #define OFFSET(STRUCT, FIELD) ((size_t) (&((STRUCT*) NULL)->FIELD))
 #define PTR_FROM_FIELD_PTR(STRUCT, FIELD, PTR) ((STRUCT *) (((char *) PTR) - OFFSET(STRUCT, FIELD)))
 
-
 // Contains all operations an allocator can do. Similar interface to sdtlibs
 // malloc, realloc and free.
 typedef struct allocator_vtbl {
@@ -89,15 +88,7 @@ typedef struct arena_allocator {
 	allocator_t allocator;
 	size_t size;
 	size_t capacity;
-	// this may grow outside the allocated data. When data is not large enough,
-	// the backing allocator will be used to allocate exactly what the user
-	// asked for, and the total_allocated will grow for each such allocation.
-	// On the next reset if total_allocated is larger than capacity, we know
-	// that there are allocations outside the large buffer, so we reset the
-	// allocator, and allocate a new buffer that is the size of
-	// total_allocated, and set the new size of the capacity. Otherwise the
-	// size is just reset to 0. plus something else I think I forgot.
-	size_t total_allocated_bytes;
+	size_t bytes_outside_data;
 	uint8_t *data;
 } arena_allocator_t;