Optimise Int32.unsigned_to_int on 64-bit (#10244)

ocaml · Mar 2, 2021 · a477306 · a477306
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diff --git a/Changes b/Changes
@@ -82,6 +82,9 @@ Working version
 - #10228: Better code-generation for inlined comparisons
   (Stephen Dolan, review by Alain Frisch and Xavier Leroy)
 
+- #10244: Optimise Int32.unsigned_to_int
+  (Fabian Hemmer, review by Stephen Dolan and Xavier Leroy)
+
 ### Standard library:
 
 - #9533: Added String.starts_with and String.ends_with.

diff --git a/stdlib/int32.ml b/stdlib/int32.ml
@@ -63,8 +63,8 @@ let unsigned_to_int =
           None
   | 64 ->
       (* So that it compiles in 32-bit *)
-      let move = int_of_string "0x1_0000_0000" in
-      fun n -> let i = to_int n in Some (if i < 0 then i + move else i)
+      let mask = 0xFFFF lsl 16 lor 0xFFFF in
+      fun n -> Some (to_int n land mask)
   | _ ->
       assert false