medfall

commit 7f814c553b92fa2a7b7dd29b06f9344dd47dd323
parent 01321e760c4a5e25713d1aa0cfec577a12440bfe
Author: Michael Savage <mikejsavage@gmail.com>
Date:   Sun Aug 16 11:56:28 +0200

Add memory arena implementation

Diffstat:
intrinsics.h
 | 
4
++++
memory_arena.cc
 | 
42
++++++++++++++++++++++++++++++++++++++++++
memory_arena.h
 | 
26
++++++++++++++++++++++++++
3 files changed, 72 insertions(+), 0 deletions(-)
diff --git a/intrinsics.h b/intrinsics.h
@@ -37,11 +37,15 @@ inline void mike_assert( const bool predicate, const char * const message ) {
 #define assert( predicate ) mike_assert( predicate, "assertion failed at " __FILE__ " line " STRINGIFY( __LINE__ ) ": " #predicate )
 
 #define is_power_of_2( n ) ( ( ( n ) & ( ( n ) - 1 ) ) == 0 )
+
 #define align_power_of_2( n, alignment ) ( ( ( n ) + ( alignment ) - 1 ) & ~( ( alignment ) - 1 ) )
 #define align4( n ) align_power_of_2( n, 4 )
 #define align8( n ) align_power_of_2( n, 8 )
 #define align16( n ) align_power_of_2( n, 16 )
 
+// TODO: clashes with some crap in std::string
+#define align_TODO( n, alignment ) ( ( ( n ) + ( alignment ) - 1 ) / ( alignment ) * ( alignment ) )
+
 inline size_t kilobytes( const size_t kb ) {
 	return kb * 1024;
 }
diff --git a/memory_arena.cc b/memory_arena.cc
@@ -0,0 +1,42 @@
+#include "intrinsics.h"
+#include "memory_arena.h"
+
+void memarena_init( MemoryArena * const arena, u8 * const memory, const size_t size ) {
+	arena->memory = memory;
+	arena->size = size;
+	arena->used = 0;
+}
+
+u8 * memarena_push_size( MemoryArena * const arena, const size_t size, const size_t alignment ) {
+	size_t base_index = align_TODO( arena->used, alignment );
+	size_t new_used = arena->used + size + ( base_index - arena->used );
+	assert( new_used <= arena->size );
+	assert( new_used >= arena->used );
+
+	arena->used = new_used;
+
+	return arena->memory + base_index;
+}
+
+void memarena_clear( MemoryArena * const arena ) {
+	arena->used = 0;
+	arena->num_checkpoints = 0;
+}
+
+MemoryArenaCheckpoint memarena_checkpoint( MemoryArena * const arena ) {
+	MemoryArenaCheckpoint cp = { };
+	// cp.arena = arena;
+	cp.used = arena->used;
+	arena->num_checkpoints++;
+
+	return cp;
+}
+
+void memarena_restore( MemoryArena * arena, MemoryArenaCheckpoint * const cp ) {
+	assert( arena->num_checkpoints > 0 );
+	assert( !cp->restored );
+
+	arena->used = cp->used;
+	arena->num_checkpoints--;
+	cp->restored = true;
+}
diff --git a/memory_arena.h b/memory_arena.h
@@ -0,0 +1,26 @@
+#ifndef _MEMORY_ARENA_H_
+#define _MEMORY_ARENA_H_
+
+#include "intrinsics.h"
+
+struct MemoryArena {
+	u8 * memory;
+	size_t size;
+	size_t used;
+	size_t num_checkpoints;
+};
+
+struct MemoryArenaCheckpoint {
+	// MemoryArena * arena;
+	size_t used;
+	bool restored;
+};
+
+void memarena_init( MemoryArena * const arena, u8 * const memory, const size_t size );
+u8 * memarena_push_size( MemoryArena * const arena, const size_t size, const size_t alignment = 4 );
+#define memarena_push_type( arena, type ) ( ( type * ) memarena_push_size( arena, sizeof( type ), sizeof( type ) ) )
+void memarena_clear( MemoryArena * const arena );
+MemoryArenaCheckpoint memarena_checkpoint( MemoryArena * const arena );
+void memarena_restore( MemoryArena * arena, MemoryArenaCheckpoint * const cp );
+
+#endif // _MEMORY_ARENA_H_