From 9c93b37557ad95dd28df71718c484a13806dd544 Mon Sep 17 00:00:00 2001
From: olemorud <ole.kristian.morud@cern.ch>
Date: Sun, 14 May 2023 23:50:43 +0200
Subject: [PATCH] Initial commit

---
 arena.h            | 12 +++++++++
 arena_alloc.c      | 63 ++++++++++++++++++++++++++++++++++++++++++++++
 test_arena_alloc.c | 31 +++++++++++++++++++++++
 3 files changed, 106 insertions(+)
 create mode 100644 arena.h
 create mode 100644 arena_alloc.c
 create mode 100644 test_arena_alloc.c

diff --git a/arena.h b/arena.h
new file mode 100644
index 0000000..d07e761
--- /dev/null
+++ b/arena.h
@@ -0,0 +1,12 @@
+
+#include <stddef.h> // ptrdiff_t
+
+struct arena {
+    void *start,
+         *next;
+    ptrdiff_t cap;
+} __attribute__((aligned(64)));
+
+struct arena* arena_new();
+void arena_reset(struct arena *a);
+void* arena_alloc(struct arena *a, size_t len);
diff --git a/arena_alloc.c b/arena_alloc.c
new file mode 100644
index 0000000..cbf9f49
--- /dev/null
+++ b/arena_alloc.c
@@ -0,0 +1,63 @@
+
+
+#include "arena.h"
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+#include <stddef.h> // ptrdiff_t
+#include <sys/mman.h>
+
+#define ARENA_PAGES ((size_t)(128))
+
+#define ALIGN 1
+
+struct arena* arena_new()
+{
+    size_t page_size = sysconf(_SC_PAGE_SIZE);
+    size_t size = page_size * ARENA_PAGES;
+
+    void *p = mmap(
+            NULL,
+            size,
+            PROT_READ | PROT_WRITE, 
+            MAP_ANONYMOUS | MAP_PRIVATE,
+            -1, /* man mmap(2): "[...], some implementations require fd to be
+                   -1 if MAP_ANONYMOUS is specified [...]" */
+            0
+    );
+
+    if (p == MAP_FAILED) {
+        return NULL;
+    }
+
+    struct arena a = {
+        .start = p + sizeof(struct arena),
+        .next  = p + sizeof(struct arena),
+        .cap   = size
+    };
+
+    memcpy(p, &a, sizeof a);
+
+    return p;
+}
+
+
+void arena_reset(struct arena *a)
+{
+    a->next = a->start;
+}
+
+
+void* arena_alloc(struct arena *a, size_t len)
+{
+    void *p = a->next;
+    a->next += len;
+
+    if (a->next - a->start >= a->cap) {
+        errno = ENOMEM;
+        return NULL;
+    }
+
+    return p;
+}
+
diff --git a/test_arena_alloc.c b/test_arena_alloc.c
new file mode 100644
index 0000000..cef10bc
--- /dev/null
+++ b/test_arena_alloc.c
@@ -0,0 +1,31 @@
+
+
+
+// _start test_arena_alloc.c
+#include "arena.h"
+#include <err.h>
+#include <stdio.h>
+#include <errno.h>
+
+static struct arena *default_arena = NULL;
+
+int main()
+{
+    default_arena = arena_new();
+
+    if (default_arena == NULL) {
+        err(errno, "failed to allocate arena");
+    }
+
+    char *p = arena_alloc(default_arena, sizeof p * 11);
+
+    for (size_t i=0; i<10; ++i) {
+        p[i] = 'A';
+    }
+
+    p[10] = '\0';
+
+    printf("%s", p);
+
+    return 0;
+}