+type t = { length : int;
+ bits : string; }
+
+let create ?(init=false) size =
+ let i = if init then '\xff' else '\x00' in
+ { length = size;
+ bits = String.make (1 + size / 8) i
+ }
+
+let length v = v.length
+
+let unsafe_get v n =
+ let i = n / 8
+ and j = n mod 8 in
+ (((Char.code (String.unsafe_get v.bits i)) lsr j) land 1) == 1
+
+
+let unsafe_set v n (b:bool) =
+ let x : int = Obj.magic b in
+ let i = n / 8
+ and j = n mod 8 in
+ let m = 1 lsl j in
+ let w = Char.code (String.unsafe_get v.bits i) in
+ let w = (w land lnot m) lor (~-x land m) in
+ String.unsafe_set v.bits i (Char.unsafe_chr (w land 0xff))
+;;
+
+let get v n =
+ if n < 0 || n >= v.length then failwith "Bitvector.get"
+ else unsafe_get v n
+;;
+
+let set v n b =
+ if n < 0 || n >= v.length then failwith "Bitvector.set"
+ else unsafe_set v n b
+;;