Defined arena for memory management.

1 files changed, 94 insertions, 0 deletions

diff --git a/wv_mem.c b/wv_mem.c
new file mode 100644
index 0000000..0bb32dc
--- /dev/null
+++ b/wv_mem.c
@@ -0,0 +1,94 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "wv_mem.h"
+#include "wv_err.h"
+
+/* Detect alignment pre-C11 */
+union wv_max_align { long l; double d; void *p; };
+
+#define WV_ALIGNOF(type) offsetof(struct { char c; type member; }, member)
+#define WV_ALIGNMENT  WV_ALIGNOF(union wv_max_align)
+#define WV_ALIGN_MASK (WV_ALIGNMENT - 1)
+
+#define WV_ARENA_MIN_SIZE  (256 * 1024)
+#define WV_ARENA_RESERVED  WV_ALIGNMENT  /* Reserve 0 as the sentinel "null" ref */
+
+struct wv_arena *wv_arena_create(size_t n)
+{
+	struct wv_arena *arena;
+
+	if (n < WV_ARENA_MIN_SIZE)
+		n = WV_ARENA_MIN_SIZE;
+
+	arena = malloc(sizeof(struct wv_arena));
+	if (arena == NULL)
+		err(1, "malloc arena struct");
+
+	arena->buf = malloc(n);
+	if (arena->buf == NULL)
+		err(1, "malloc arena buffer");
+
+	arena->size = n;
+	arena->offset = WV_ARENA_RESERVED;
+
+	return arena;
+}
+
+wv_ref wv_alloc(struct wv_arena *arena, size_t n)
+{
+	wv_ref ref;
+	unsigned char *new_buf;
+	size_t aligned_n, new_size;
+
+	if (n == 0)
+		errx(1, "wv_alloc: zero-size allocation");
+
+	if (n > SIZE_MAX - WV_ALIGN_MASK)
+		errx(1, "wv_alloc: allocation size overflow");
+
+	aligned_n = (n + WV_ALIGN_MASK) & ~WV_ALIGN_MASK;
+
+	if (aligned_n > SIZE_MAX - arena->offset)
+		errx(1, "wv_alloc: arena offset overflow");
+
+	if (arena->offset + aligned_n > arena->size) {
+		new_size = arena->size;
+		while (new_size < arena->offset + aligned_n) {
+			if (new_size > SIZE_MAX / 2)
+				errx(1, "wv_alloc: arena growth overflow");
+			new_size *= 2;
+		}
+
+		new_buf = realloc(arena->buf, new_size);
+		if (new_buf == NULL)
+			err(1, "realloc arena failed at %zu bytes", new_size);
+
+		arena->buf  = new_buf;
+		arena->size = new_size;
+	}
+
+	ref = (wv_ref)arena->offset;
+	arena->offset += aligned_n;
+	return ref;
+}
+
+void wv_arena_reset(struct wv_arena *arena)
+{
+	if (arena == NULL)
+		return;
+
+	memset(arena->buf, 0, arena->offset);
+	arena->offset = WV_ARENA_RESERVED;
+}
+
+void wv_arena_destroy(struct wv_arena *arena)
+{
+	if (arena == NULL)
+		return;
+
+	free(arena->buf);
+	free(arena);
+}
+