From 4b9ab2ec5acf2ecf2e96c38733a835b964664171 Mon Sep 17 00:00:00 2001
From: Omniscient <17525998+omnisci3nce@users.noreply.github.com>
Date: Sun, 25 Feb 2024 11:02:46 +1100
Subject: add an arena allocator first impl

---
 src/log.h            |  2 ++
 src/maths/geometry.h |  2 +-
 src/std/mem.c        | 26 ++++++++++++++++++++++++++
 src/std/mem.h        | 12 ++++++++++--
 tests/arena_tests.c  | 12 ++++++++++++
 5 files changed, 51 insertions(+), 3 deletions(-)
 create mode 100644 src/std/mem.c
 create mode 100644 tests/arena_tests.c

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/maths/geometry.h b/src/maths/geometry.h
index 6f4797b..937c38a 100644
--- a/src/maths/geometry.h
+++ b/src/maths/geometry.h
@@ -4,7 +4,7 @@
  * @brief Shapes and intersections between them
  * @version 0.1
  * @date 2024-02-24
- * 
+ *
  * @copyright Copyright (c) 2024
  */
 #pragma once
diff --git a/src/std/mem.c b/src/std/mem.c
new file mode 100644
index 0000000..c30f76d
--- /dev/null
+++ b/src/std/mem.c
@@ -0,0 +1,26 @@
+#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->begin & (align - 1);
+  ptrdiff_t available = a->end - a->begin - 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, .end = backing_buffer + (ptrdiff_t)capacity };
+}
\ No newline at end of file
diff --git a/src/std/mem.h b/src/std/mem.h
index 74222a7..75b6d2a 100644
--- a/src/std/mem.h
+++ b/src/std/mem.h
@@ -9,6 +9,14 @@
  */
 #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* 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);
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
-- 
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