persistent bit vectors

.gitignore

@@ -22,3 +22,4 @@ sieve.opt
 
 bench.exe
 perf.data
+bench_pbv.exe

CHANGES.md

@@ -1,4 +1,6 @@
 
+  - new module [Pbv] for persistent bit vectors
+
 # 2.1 (22/08/2025)
   - fixed bug in `random`
   - fixed negative `max_length` on JavaScript platform

README.md

@@ -10,8 +10,12 @@ opam install bitv
 
 ## Usage
 
-The library provides a single module, `Bitv`.  The documentation is
-available [here](https://backtracking.github.io/bitv).
+The library provides two modules:
+- `Bitv`, for imperative bit vectors;
+- `Pbv`, for persistence bit vectors.
+
+The documentation is available
+[here](https://backtracking.github.io/bitv).
 
 ## Bug reports
 

bench_pbv.ml

@@ -0,0 +1,27 @@
+
+(* sandbox to test performance *)
+
+open Format
+
+let time f x =
+  let open Unix in
+  let u = (times()).tms_utime in
+  let y = f x in
+  let ut = (times()).tms_utime -. u in
+  printf "%2.2f@." ut;
+  y
+
+open Bitv__Pbv
+
+let () = Random.init 42
+let n = int_of_string Sys.argv.(1)
+
+module M = Small(struct let size = Sys.int_size end)
+open M
+let v = init 63 (fun i -> i < n)
+let () = printf "v = %a@." print v
+let f v =
+  let s = ref 0 in
+  iter_subsets (fun v -> s := !s + pop v) v;
+  printf "sum = %d@." !s
+let () = time f v

bitv.mli

@@ -18,7 +18,11 @@
     the same operations as module [Array]. It also provides bitwise operations
     and conversions to/from integer types.
 
-    In the following, [false] stands for bit 0 and [true] for bit 1. *)
+    In the following, [false] stands for bit 0 and [true] for bit 1.
+
+    This is an imperative data structure. For persistence bit vectors,
+    see module [Pbv].
+*)
 
 type t
 (** the type of bit vectors *)
@@ -27,7 +31,7 @@ type t
 
 val create : int -> bool -> t
 (** [(Bitv.create n b)] creates a new bit vector of length [n],
-   initialized with [b]. *)
+    initialized with [b]. *)
 
 val init : int -> (int -> bool) -> t
 (** [(Bitv.init n f)] returns a fresh vector of length [n],

dune

@@ -2,7 +2,7 @@
  (public_name bitv)
  (flags
   (:standard -w -32))
- (modules bitv))
+ (modules bitv pbv))
 
 (library
  (public_name bitv.string)
@@ -15,6 +15,13 @@
  (modules test)
  (libraries bitv))
 
+(test
+ (name test_pbv)
+ (modules test_pbv)
+ (flags
+  (:standard -w -32))
+ (libraries bitv))
+
 (test
  (name sieve)
  (modules sieve)
@@ -25,3 +32,9 @@
  (modules bench)
  (promote (until-clean))
  (libraries unix bitv))
+
+(executable
+ (name bench_pbv)
+ (modules bench_pbv)
+ (promote (until-clean))
+ (libraries unix bitv))