Getting allocators and types under control.

jh_mem.h

@@ -15,9 +15,79 @@ 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"
+
+NOTE:
+This is intended to be used with the jh.h header.
+And will require jh.h as it uses the typedefs defined in that file. 
+
 */
 
 #ifndef JH_MEM_INCLUDED
 #define JH_MEM_INCLUDED
 
+#ifndef DEFAULT_ALIGNMENT
+#define DEFAULT_ALIGNMENT (2*sizeof(void *))
+#endif
+
+typedef struct Arena Arena;
+struct Arena {
+	u8      *data;
+	usize   data_len;
+	usize   prev_offset;
+	usize   curr_offset;
+};
+
+bool 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);
+
+// -------------------------------------- 
+// -------------------------------------- 
+// implementation Below
+// -------------------------------------- 
+
+
+// -------------------------------------- 
+// Arena Functions Start
+// -------------------------------------- 
+
+bool is_power_of_two(uintptr_t x) {
+	return (x & (x-1)) == 0;
+}
+
+uptr align_forward(uptr ptr, usize align) {
+	uptr p, a, modulo;
+	
+	assert(is_power_of_two(align));
+
+	p = ptr;
+	a = (uptr)align;
+	modulo = p & (a-1);
+
+	if (modulo != 0) {
+		// If 'p' address is not aligned. 
+		// push the address to the next value which is aligned
+		p += a - modulo;
+	}
+
+	return p;
+}
+
+void *arena_alloc_align(Arena *a, usize size, usize align) {
+	uptr current_ptr = (uptr)a->data + (uptr)a->curr_offset;
+	uptr offset = align_forward(current_ptr, align);
+
+	// Change to relative offset
+	offset -= (uptr)a->data;
+}
+
+void *arena_alloc(Arena *a, size_t size) {
+	return arena_alloc_align(a, size, DEFAULT_ALIGNMENT);
+}
+
+// -------------------------------------- 
+// Arena Functions END
+// -------------------------------------- 
+
 #endif