Improve hash function

- Hash chunks in the same order as the C implementation.
  (submitted a change to the C stubs to get the same result on all platforms:
   ocaml/Zarith#145)
- Call caml_hash_mix_final to compute the final hash value and restrict
  the result to a positive 31-bit integer.

Signed-off-by: Jérôme Vouillon <[email protected]>

runtime.js

@@ -19,12 +19,12 @@ function ml_z_mul_overflows(x,y){
 
 //external init: unit -> unit
 //Provides: ml_z_init
-//Requires: caml_zarith_marshal, caml_zarith_unmarshal, caml_custom_ops, ml_z_hash, ml_z_compare
+//Requires: caml_zarith_marshal, caml_zarith_unmarshal, caml_custom_ops, jsoo_z_hash, ml_z_compare
 function ml_z_init(unit) {
   caml_custom_ops['_z'] =
     { serialize : caml_zarith_marshal,
       deserialize : caml_zarith_unmarshal,
-      hash : ml_z_hash,
+      hash : jsoo_z_hash,
       compare : ml_z_compare,
     };
   return 0 }
@@ -498,13 +498,15 @@ function ml_z_pow(z1, i1) {
   return ml_z_normalize(bigInt(z1).pow(i1));
 }
 
-//external hash: t -> int
-//Provides: ml_z_hash const
+//Provides: jsoo_z_hash const
 //Requires: bigInt, caml_hash_mix_int
-function ml_z_hash(z1) {
-  var a = bigInt(z1).toArray(Math.pow(2, 32));
+function jsoo_z_hash(z1) {
+  if (!z1) return 0;
+
+  z1 = bigInt(z1)
+  var a = z1.toArray(Math.pow(2, 32));
   var acc = 0;
-  for (var i = 0; i < a.value.length; i++) {
+  for (var i = a.value.length - 1; i >= 0 ; i--) {
     acc = caml_hash_mix_int(acc, a.value[i]);
   }
   if(a.value.length % 2 != 0) {
@@ -513,7 +515,14 @@ function ml_z_hash(z1) {
   if(a.isNegative){
     acc = acc + 1
   }
-  return acc | 0
+  return acc | 0;
+}
+
+//external hash: t -> int
+//Provides: ml_z_hash const
+//Requires: jsoo_z_hash, caml_hash_mix_final, caml_hash_mix_int
+function ml_z_hash(z1) {
+  return caml_hash_mix_final(caml_hash_mix_int(0, jsoo_z_hash(z1))) & 0x3FFFFFFF
 }
 
 //external to_bits: t -> string

test/base.ml

@@ -35,6 +35,6 @@ module Ml_z_hash = struct
     Static.quickcheck ~f:(fun x -> [%message (x : t) (hash x : int)]) ();
     [%expect
       {|
-      ((hash 1b8bb80aec20e0754b953210f67f7eca) (uniqueness_rate 85.742188)) |}]
+      ((hash 06e8f27264e3dcc3b402b536aa76725a) (uniqueness_rate 85.742188)) |}]
   ;;
 end