start work on new interpreter

next/core/arena.c

@@ -0,0 +1,26 @@
+#include <growl.h>
+#include <stdlib.h>
+#include <string.h>
+
+void growl_arena_init(GrowlGCArena *arena, size_t size) {
+  arena->start = arena->free = malloc(size);
+  if (arena->start == NULL)
+    abort();
+  arena->end = arena->start + size;
+}
+
+void growl_arena_free(GrowlGCArena *arena) {
+  free(arena->start);
+  arena->start = arena->end = arena->free = NULL;
+}
+
+void *growl_arena_alloc(GrowlGCArena *arena, size_t size, size_t align,
+                        size_t count) {
+  ptrdiff_t padding = -(uintptr_t)arena->start & (align - 1);
+  ptrdiff_t available = arena->end - arena->start - padding;
+  if (available < 0 || count > available / size)
+    abort();
+  void *p = arena->start + padding;
+  arena->start += padding + count * size;
+  return memset(p, 0, count * size);
+}