1 files changed, 56 insertions, 0 deletions
diff --git a/src/arena.c b/src/arena.c
new file mode 100644
index 0000000..3782b79
--- /dev/null
+++ b/src/arena.c
@@ -0,0 +1,56 @@
+#include "arena.h"
+
+#include <assert.h>         // assert
+#include <stdint.h>         // uintptr_t
+#include <stdio.h>          // fprintf
+#include <stdlib.h>         // abort, malloc
+#include <stdnoreturn.h>    // noreturn
+#include <string.h>         // memset
+
+static noreturn void arena_panic(const char *reason) {
+	fprintf(stderr, "Memory allocation failed: %s", reason);
+	abort();
+}
+
+struct arena arena_create(size_t capacity) {
+	struct arena arena = {
+		.root = malloc(capacity),
+		.capacity = capacity,
+		.used = 0,
+	};
+	if (arena.root == NULL) {
+		arena_panic("cannot allocate system memory");
+	}
+	return arena;
+}
+
+void *arena_alloc(struct arena *arena, size_t size, size_t alignment, unsigned flags) {
+	// Alignment must be a power of two.
+	// See: https://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
+	assert(alignment != 0 && (alignment & (alignment - 1)) == 0);
+	size_t padding = -(uintptr_t)(arena->root + arena->used) & (alignment - 1);
+
+        // If no more memory is available, we fall back to our error strategy.
+	assert(arena->capacity >= arena->used);
+        if (arena->used + padding + size > arena->capacity) {
+		if (flags & ARENA_NO_PANIC) {
+			return NULL;
+		} else {
+			arena_panic("out of preallocated memory");
+		}
+	}
+
+	// Reserve memory from arena.
+	void *ptr = arena->root + arena->used + padding;
+	arena->used += padding + size;
+
+	if (~flags & ARENA_NO_ZERO) {
+		memset(ptr, 0, size);
+	}
+
+	return ptr;
+}
+
+void arena_destroy(struct arena *arena) {
+	free(arena->root);
+}