4 files changed, 59 insertions, 2 deletions
diff --git a/src/log.h b/src/log.h
index e7a90ea..b0c355b 100644
--- a/src/log.h
+++ b/src/log.h
@@ -1,6 +1,8 @@
 #pragma once
 
 #include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
 
 #define ERROR_EXIT(...)           \
   {                               \
diff --git a/src/std/mem.c b/src/std/mem.c
new file mode 100644
index 0000000..f5b92d4
--- /dev/null
+++ b/src/std/mem.c
@@ -0,0 +1,32 @@
+#include "mem.h"
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include "log.h"
+
+#ifndef DEFAULT_ALIGNMENT
+#define DEFAULT_ALIGNMENT (2 * sizeof(void*))
+#endif
+
+void* arena_alloc_align(arena* a, size_t size, size_t align) {
+  ptrdiff_t padding = -(uintptr_t)a->curr & (align - 1);
+  ptrdiff_t available = a->end - a->curr - padding;
+  TRACE("Padding %td available %td", padding, available);
+  if (available < 0 || (ptrdiff_t)size > available) {
+    ERROR_EXIT("Arena ran out of memory\n");
+  }
+  void* p = a->begin + padding;
+  a->begin += padding + size;
+  return memset(p, 0, size);
+}
+void* arena_alloc(arena* a, size_t size) { return arena_alloc_align(a, size, DEFAULT_ALIGNMENT); }
+
+arena arena_create(void* backing_buffer, size_t capacity) {
+  return (arena){ .begin = backing_buffer,
+                  .curr = backing_buffer,
+                  .end = backing_buffer + (ptrdiff_t)capacity };
+}
+
+void arena_free_all(arena* a) {
+  a->curr = a->begin;  // pop everything at once and reset to the start.
+}
+\ No newline at end of file
diff --git a/src/std/mem.h b/src/std/mem.h
index 74222a7..c3ec61d 100644
--- a/src/std/mem.h
+++ b/src/std/mem.h
@@ -9,6 +9,17 @@
  */
 #pragma once
 
-#include "defines.h"
+#include <stddef.h>
 
-typedef void* (*alloc)(size_t amount);
-\ No newline at end of file
+// Inspired by https://nullprogram.com/blog/2023/09/27/
+typedef struct arena {
+  char* begin;
+  char* curr;
+  char* end;
+} arena;
+
+arena arena_create(void* backing_buffer, size_t capacity);
+void* arena_alloc(arena* a, size_t size);
+void* arena_alloc_align(arena* a, size_t size, size_t align);
+void arena_free_all(arena* a);
+// TODO: arena_resize
+\ No newline at end of file
diff --git a/tests/arena_tests.c b/tests/arena_tests.c
new file mode 100644
index 0000000..88fc21b
--- /dev/null
+++ b/tests/arena_tests.c
@@ -0,0 +1,12 @@
+/*
+size_t arena_size = 16;
+  arena scratch = arena_create(malloc(arena_size), arena_size);
+
+  i32* int_ptr = arena_alloc(&scratch, sizeof(i32));
+  i32* b = arena_alloc(&scratch, sizeof(i32));
+  i32* c = arena_alloc(&scratch, sizeof(i32));
+  *int_ptr = 55;
+  printf("Int pointer %d %p\n", (*int_ptr), int_ptr);
+
+  // will abort on second arena alloc
+*/
+\ No newline at end of file