In Z, replace size with bit_length, complete JSBN bindings

src/lib/election.ml

@@ -50,7 +50,7 @@ module MakeSimpleMonad (G : GROUP) = struct
   let fail e = raise e
 
   let random q =
-    let size = Z.size q * Sys.word_size / 8 in
+    let size = Z.bit_length q / 8 + 1 in
     fun () ->
       let r = random_string (Lazy.force prng) size in
       Z.(of_bits r mod q)

src/lib/platform.mli

@@ -52,7 +52,7 @@ module Z : sig
   val powm : t -> t -> t -> t
   val invert : t -> t -> t
   val probab_prime : t -> int -> int
-  val size : t -> int
+  val bit_length : t -> int
   val of_bits : string -> t
 end
 

src/platform/js/platform.ml

@@ -61,6 +61,7 @@ module Z = struct
   let lt x y = compare x y < 0
   let powm x y m = meth_call x "modPow" [| y; m |]
   let invert x m = meth_call x "modInverse" [| m |]
+  let bit_length x = meth_call x "bitLength" [| |]
 
   let erem x y =
     let r = x mod y in
@@ -70,8 +71,15 @@ module Z = struct
     meth_call x "isProbablePrime" [| |] |>
     Js.float_of_number |> int_of_float
 
-  let size x = assert false
-  let of_bits x = assert false
+  let z256 = of_int 256
+
+  let of_bits x =
+    let n = String.length x in
+    let rec loop res i =
+      if i >= 0
+      then loop (res * z256 + of_int (int_of_char x.[i])) (pred i)
+      else res
+    in loop zero (pred n)
 end
 
 type datetime

src/platform/native/platform.ml

@@ -92,6 +92,7 @@ let random_string = Cryptokit.Random.string
 module Z = struct
   include Z
   let ( =% ) = equal
+  let bit_length x = Pervasives.(String.length (to_bits x) * 8)
 end
 
 open CalendarLib

src/tool/tool_js.ml

@@ -95,6 +95,11 @@ module Tests = struct
     check "neq" (fun () -> Z.(not (c =% d)));
     check "geq" (fun () -> Z.geq c d);
     check "lt" (fun () -> Z.lt d c);
+    let i = Z.of_string "272660753928370030481696309961224617984" in
+    check "bit_length" (fun () -> Z.bit_length i = 128);
+    let j = Z.of_bits "\x81\xab\xd3\xed\x0b\x19\x2e\x40\x7a\xca" in
+    let k = Z.of_string "956173156978067279948673" in
+    check "of_bits" (fun () -> Z.(j =% k));
     Printf.ksprintf alert "%d tests were successful!" !ntests
 
   let cmds = ["do_unit_tests", unit_tests]

src/web/web_common.ml

@@ -61,7 +61,7 @@ module MakeLwtRandom (X : LWT_RNG) = struct
   let fail = Lwt.fail
 
   let random q =
-    let size = Z.size q * Sys.word_size / 8 in
+    let size = Z.bit_length q / 8 + 1 in
     lwt rng = X.rng in
     let r = random_string rng size in
     return Z.(of_bits r mod q)