Include super basic memory arena

arena.h

@@ -0,0 +1,47 @@
+#ifndef ARENA_H
+#define ARENA_H
+
+typedef enum {
+    ARENA_ZERO     = 1 << 0,
+    ARENA_SOFTFAIL = 1 << 1,
+} arena_flags_t;
+
+// More or less taken from https://nullprogram.com/blog/2023/09/27/
+typedef struct {
+    uint8_t *begin;
+    uint8_t *end;
+} arena_t;
+
+arena_t arena_create(ptrdiff_t capacity)
+{
+    arena_t a = {0};
+    a.begin = malloc(capacity);
+    a.end = a.begin ? a.begin + capacity : 0;
+    return a;
+}
+
+
+void *arena_alloc(arena_t *a, ptrdiff_t size, ptrdiff_t align, ptrdiff_t count, arena_flags_t flags)
+{
+    ptrdiff_t padding = -(uintptr_t)a->begin & (align - 1);
+    ptrdiff_t available = a->end - a->begin - padding;
+    if (available < 0 || count > available/size)
+    {
+        // TODO: Decide what to do on oom
+        if (flags & ARENA_SOFTFAIL)
+            return 0;
+        else
+            abort();
+    }
+    void *p = a->begin + padding;
+    a->begin += padding + count*size;
+    return flags & ARENA_ZERO ? p : memset(p, 0, count*size);
+}
+
+#define arena_reserve(arena, type, count, flags) (type *)arena_alloc(arena, sizeof(type), _Alignof(type), count, flags)
+
+#define KB 1024
+#define MB 1024*KB
+#define GB 1024*MB
+
+#endif