Add makefile and restructure

src/alloc_backend.c

@@ -0,0 +1,30 @@
+
+#include "alloc_backend.h"
+
+#define _GNU_SOURCE
+#include <sys/mman.h>
+
+/*
+ * Separate function to make switching
+ * allocation backend easier
+ *
+ * must take size_t size as an argument
+ * must return NULL on failure
+ */
+void* call_alloc_backend(size_t size)
+{
+    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;
+
+    return p;
+}

src/alloc_backend.h

@@ -0,0 +1,9 @@
+
+#ifndef ALLOC_BACKEND_H
+#define ALLOC_BACKEND_H
+
+#include <stddef.h>
+
+void* call_alloc_backend(size_t size);
+
+#endif

src/arena.c

@@ -0,0 +1,60 @@
+
+
+#include "arena.h"
+#include "alloc_backend.h"
+
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+
+#define ARENA_SIZE ((size_t)(128*sysconf(_SC_PAGE_SIZE)))
+
+/*
+ * Allocates and returns new arena
+ */
+struct arena* arena_new()
+{
+    size_t size = ARENA_SIZE;
+
+    unsigned char *p = call_alloc_backend(size);
+
+    if (p == NULL)
+        return NULL;
+
+    struct arena a = {
+        .begin = p + sizeof(struct arena),
+        .next  = p + sizeof(struct arena),
+        .cap   = size
+    };
+
+    memcpy(p, &a, sizeof a);
+
+    return (struct arena*)p;
+}
+
+
+/*
+ * Frees all memory in arena
+ */
+void arena_reset(struct arena *a)
+{
+    a->next = a->begin;
+}
+
+
+/*
+ * Allocate new memory using arena
+ */
+void* arena_alloc(struct arena *a, size_t len)
+{
+    void *p = a->next;
+    a->next += len;
+
+    if (a->next - a->begin >= a->cap) {
+        errno = ENOMEM;
+        return NULL;
+    }
+
+    return p;
+}
+

src/arena.h

@@ -0,0 +1,19 @@
+
+#ifndef ARENA_H
+#define ARENA_H
+
+
+#include <stddef.h> // ptrdiff_t
+
+struct arena {
+    unsigned char *begin,
+                  *next;
+    ptrdiff_t cap;
+};
+
+struct arena* arena_new();
+void arena_reset(struct arena *a);
+void* arena_alloc(struct arena *a, size_t len);
+
+
+#endif

src/test_arena.c

@@ -0,0 +1,44 @@
+
+
+
+// _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");
+    }
+
+	printf("\n%p\n", default_arena->next);
+
+    char *ten_A = arena_alloc(default_arena, 11 * sizeof *ten_A);
+    char *ten_B = arena_alloc(default_arena, 11 * sizeof *ten_B);
+    char *ten_C = arena_alloc(default_arena, 11 * sizeof *ten_C);
+
+    for (size_t i=0; i<10; ++i) {
+        ten_A[i] = 'A';
+        ten_B[i] = 'B';
+        ten_C[i] = 'C';
+    }
+
+    ten_A[10] = '\0';
+    ten_B[10] = '\0';
+    ten_C[10] = '\0';
+
+    printf("\n%s %s %s", ten_A, ten_B, ten_C);
+	printf("\n%p\n", default_arena->next);
+
+	arena_reset(default_arena);
+
+	printf("\n%p\n", default_arena->next);
+
+    return 0;
+}