From b76dce3d44364e14fe31f5a13cf58344c2bd9c14 Mon Sep 17 00:00:00 2001
From: fredrikr79 <fredrikrobertsen7@gmail.com>
Date: Sat, 1 Mar 2025 19:51:06 +0100
Subject: [PATCH] feat: implement utils/arena.c

---
 src/utils/arena.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++
 src/utils/arena.h | 20 +++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 src/utils/arena.c
 create mode 100644 src/utils/arena.h

diff --git a/src/utils/arena.c b/src/utils/arena.c
new file mode 100644
index 0000000..d6a7949
--- /dev/null
+++ b/src/utils/arena.c
@@ -0,0 +1,64 @@
+#include "arena.h"
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define KB(x) x * 1024
+
+void arena_init(Arena *a, size_t size) {
+  *a = (Arena){.buffer = malloc(size), .size = size, .offset = 0};
+  if (a->buffer == NULL)
+    err(EXIT_FAILURE, "malloc");
+}
+
+void *arena_alloc(Arena *a, size_t n, size_t n_size, size_t alignsize) {
+  if (alignsize == 0 || (alignsize & (alignsize - 1)) == 1) {
+    return NULL;
+  }
+
+  size_t allocation_size = n * n_size;
+
+  if (allocation_size < n_size) {
+    return NULL;
+  }
+
+  size_t total_offset = (size_t)a->offset + (size_t)a->buffer;
+  size_t padding = (~total_offset + 1) & (alignsize - 1);
+
+  total_offset += padding;
+  if (total_offset + allocation_size > (size_t)a->size + (size_t)a->buffer) {
+    return NULL;
+  }
+
+  a->offset += (padding + allocation_size);
+  memset((void *)total_offset, 0, allocation_size);
+  return (void *)total_offset;
+}
+
+void arena_reset(Arena *a) {
+  a->offset = 0;
+  memset(a->buffer, 0, a->size);
+}
+
+void arena_free(Arena *a) {
+  free(a->buffer);
+  a->size = 0;
+  a->offset = 0;
+  free(a);
+}
+
+int main(void) {
+  printf("this is the `arena.c` utility main method.\n");
+
+  Arena a = {0};
+  arena_init(&a, KB(2));
+
+  int *t = arena_alloc(&a, 6, sizeof(int), _Alignof(int));
+
+  for (int *i = t; i < t + 6; i++) {
+    printf("%d ", *i);
+  }
+
+  return 0;
+}
diff --git a/src/utils/arena.h b/src/utils/arena.h
new file mode 100644
index 0000000..dd1a50c
--- /dev/null
+++ b/src/utils/arena.h
@@ -0,0 +1,20 @@
+#ifndef ARENA_H_
+#define ARENA_H_
+
+#include <stddef.h>
+
+typedef struct {
+  char *buffer;
+  size_t size;
+  int offset;
+} Arena;
+
+void arena_init(Arena *a, size_t size);
+
+void *arena_alloc(Arena *a, size_t n, size_t n_size, size_t alignsize);
+
+void arena_reset(Arena *a);
+
+void arena_free(Arena *a);
+
+#endif // ARENA_H_