Minor performance improvements and cleanups in the implementation of …

…Int32, Int64, Nativeint (#12511)

- Define `equal` directly using `=`
- In `unsigned_to_int`, use `>=` and `<=` where appropriate
- Improve `unsigned_div` by using an ad-hoc predicate `unsigned_lt`
- Remove TODO comments that are not planned
- Fix Hacker's Delight comment

Changes

@@ -140,6 +140,10 @@ Working version
   (Nicolás Ojeda Bär, review by Jeremy Yallop, Xavier Leroy, Gabriel Scherer,
    David Allsopp)
 
+- #12511: Minor performance improvements and cleanups in the implementation
+  of modules Int32, Int64, and Nativeint
+  (Xavier Leroy, review by Gabriel Scherer and Daniel Bünzli)
+
 ### Other libraries:
 
 - #12213: Dynlink library, improve legibility of error messages

stdlib/int32.ml

@@ -57,7 +57,7 @@ let unsigned_to_int =
   | 32 ->
       let max_int = of_int Stdlib.max_int in
       fun n ->
-        if compare zero n <= 0 && compare n max_int <= 0 then
+        if n >= 0l && n <= max_int then
           Some (to_int n)
         else
           None
@@ -74,31 +74,33 @@ let to_string n = format "%d" n
 external of_string : string -> int32 = "caml_int32_of_string"
 
 let of_string_opt s =
-  (* TODO: expose a non-raising primitive directly. *)
   try Some (of_string s)
   with Failure _ -> None
 
 type t = int32
 
 let compare (x: t) (y: t) = Stdlib.compare x y
-let equal (x: t) (y: t) = compare x y = 0
+let equal (x: t) (y: t) = x = y
 
 let unsigned_compare n m =
   compare (sub n min_int) (sub m min_int)
 
+let unsigned_lt n m =
+  sub n min_int < sub m min_int
+
 let min x y : t = if x <= y then x else y
 let max x y : t = if x >= y then x else y
 
-(* Unsigned division from signed division of the same
-   bitness. See Warren Jr., Henry S. (2013). Hacker's Delight (2 ed.), Sec 9-3.
+(* Unsigned division from signed division of the same bitness.
+   See Warren Jr., Henry S. (2013). Hacker's Delight (2 ed.), Sec 9-3.
 *)
 let unsigned_div n d =
   if d < zero then
-    if unsigned_compare n d < 0 then zero else one
+    if unsigned_lt n d then zero else one
   else
     let q = shift_left (div (shift_right_logical n 1) d) 1 in
     let r = sub n (mul q d) in
-    if unsigned_compare r d >= 0 then succ q else q
+    if unsigned_lt r d then q else succ q
 
 let unsigned_rem n d =
   sub n (mul (unsigned_div n d) d)

stdlib/int64.ml

@@ -53,7 +53,7 @@ let lognot n = logxor n (-1L)
 let unsigned_to_int =
   let max_int = of_int Stdlib.max_int in
   fun n ->
-    if compare zero n <= 0 && compare n max_int <= 0 then
+    if n >= 0L && n <= max_int then
       Some (to_int n)
     else
       None
@@ -64,12 +64,9 @@ let to_string n = format "%d" n
 external of_string : string -> int64 = "caml_int64_of_string"
 
 let of_string_opt s =
-  (* TODO: expose a non-raising primitive directly. *)
   try Some (of_string s)
   with Failure _ -> None
 
-
-
 external bits_of_float : float -> int64
   = "caml_int64_bits_of_float" "caml_int64_bits_of_float_unboxed"
   [@@unboxed] [@@noalloc]
@@ -80,24 +77,27 @@ external float_of_bits : int64 -> float
 type t = int64
 
 let compare (x: t) (y: t) = Stdlib.compare x y
-let equal (x: t) (y: t) = compare x y = 0
+let equal (x: t) (y: t) = x = y
 
 let unsigned_compare n m =
   compare (sub n min_int) (sub m min_int)
 
+let unsigned_lt n m =
+  sub n min_int < sub m min_int
+
 let min x y : t = if x <= y then x else y
 let max x y : t = if x >= y then x else y
 
-(* Unsigned division from signed division of the same
-   bitness. See Warren Jr., Henry S. (2013). Hacker's Delight (2 ed.), Sec 9-3.
+(* Unsigned division from signed division of the same bitness.
+   See Warren Jr., Henry S. (2013). Hacker's Delight (2 ed.), Sec 9-3.
 *)
 let unsigned_div n d =
   if d < zero then
-    if unsigned_compare n d < 0 then zero else one
+    if unsigned_lt n d then zero else one
   else
     let q = shift_left (div (shift_right_logical n 1) d) 1 in
     let r = sub n (mul q d) in
-    if unsigned_compare r d >= 0 then succ q else q
+    if unsigned_lt r d then q else succ q
 
 let unsigned_rem n d =
   sub n (mul (unsigned_div n d) d)

stdlib/nativeint.ml

@@ -52,7 +52,7 @@ let lognot n = logxor n (-1n)
 let unsigned_to_int =
   let max_int = of_int Stdlib.max_int in
   fun n ->
-    if compare zero n <= 0 && compare n max_int <= 0 then
+    if n >= 0n && n <= max_int then
       Some (to_int n)
     else
       None
@@ -63,7 +63,6 @@ let to_string n = format "%d" n
 external of_string: string -> nativeint = "caml_nativeint_of_string"
 
 let of_string_opt s =
-  (* TODO: expose a non-raising primitive directly. *)
   try Some (of_string s)
   with Failure _ -> None
 
@@ -75,19 +74,22 @@ let equal (x: t) (y: t) = compare x y = 0
 let unsigned_compare n m =
   compare (sub n min_int) (sub m min_int)
 
+let unsigned_lt n m =
+  sub n min_int < sub m min_int
+
 let min x y : t = if x <= y then x else y
 let max x y : t = if x >= y then x else y
 
-(* Unsigned division from signed division of the same
-   bitness. See Warren Jr., Henry S. (2013). Hacker's Delight (2 ed.), Sec 9-3.
+(* Unsigned division from signed division of the same bitness.
+   See Warren Jr., Henry S. (2013). Hacker's Delight (2 ed.), Sec 9-3.
 *)
 let unsigned_div n d =
   if d < zero then
-    if unsigned_compare n d < 0 then zero else one
+    if unsigned_lt n d then zero else one
   else
     let q = shift_left (div (shift_right_logical n 1) d) 1 in
     let r = sub n (mul q d) in
-    if unsigned_compare r d >= 0 then succ q else q
+    if unsigned_lt r d then q else succ q
 
 let unsigned_rem n d =
   sub n (mul (unsigned_div n d) d)