[PATCH olang] arena: optimization: make arena 8 bits aligned

[Carlos Maniero <carlos@maniero.me>]

Non aligned data structure could have a huge impact on performance. Take
the example bellow:

  int main() {
      void *pointer = malloc(1024);

      int* data = pointer + 1;

      for (int i = 0; i < INT_MAX; i++) {
          *data += i;
      }

      printf("result = %d", *data);
  }

This are the execution results in my machine:

  pointer + 0
  time	0m1.668s
  pointer + 1
  time	0m2.285s
  pointer + 2
  time	0m2.286s
  pointer + 4
  time	0m1.722s
  pointer + 8
  time	0m1.707s

This commit changes the pointers to always return a 8 bit aligned
pointer.

Signed-off-by: Carlos Maniero <carlos@maniero.me>
---
 src/arena.c             | 2 +-
 tests/unit/arena_test.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/arena.c b/src/arena.c
index ae33e6a..63662e3 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -35,7 +35,7 @@ arena_alloc(arena_t *arena, size_t size)
         return NULL;
     }
     void *pointer = arena->region + arena->offset;
-    arena->offset += size;
+    arena->offset += size + (size % 8);
     return pointer;
 }
 
diff --git a/tests/unit/arena_test.c b/tests/unit/arena_test.c
index 6310795..7808b64 100644
--- a/tests/unit/arena_test.c
+++ b/tests/unit/arena_test.c
@@ -21,7 +21,7 @@
 static MunitResult
 arena_test(const MunitParameter params[], void *user_data_or_fixture)
 {
-    arena_t arena = arena_new(sizeof(int) * 2);
+    arena_t arena = arena_new(16);
 
     int *a = arena_alloc(&arena, sizeof(int));
     *a = 1;
-- 
2.34.1