fix Ext_int.int32_pow to behave like JavaScript

Author: cometkim

compiler/ext/ext_int.ml

@@ -35,10 +35,14 @@ let int32_unsigned_to_int (n : int32) : int =
   let i = Int32.to_int n in
   if i < 0 then i + move else i
 
-let rec int32_pow (a : int32) = function
-  | 0l -> 1l
-  | 1l -> a
-  | n ->
-    let b = int32_pow a (Int32.div n 2l) in
-    let b = Int32.mul b b in
-    Int32.mul b (if Int32.rem n 2l = 0l then 1l else a)
+let int32_pow (x : int32) (y : int32) =
+  let x_float = Int32.to_float x in
+  let y_float = Int32.to_float y in
+  let result = x_float ** y_float in
+  let truncated =
+    if result > 2147483647.0 || result < -2147483648.0 then
+      let i = int_of_float result in
+      i land 0xFFFFFFFF
+    else int_of_float result
+  in
+  Int32.of_int truncated

tests/tests/src/exponentiation_test.mjs

@@ -36,9 +36,11 @@ eq("File \"exponentiation_test.res\", line 19, characters 5-12", -2147483648, in
 
 eq("File \"exponentiation_test.res\", line 20, characters 5-12", 0, intPow(2, 32));
 
-eq("File \"exponentiation_test.res\", line 21, characters 5-12", 1, intPow(2147483647, 2));
+eq("File \"exponentiation_test.res\", line 21, characters 5-12", 0, intPow(2147483647, 2));
 
-eq("File \"exponentiation_test.res\", line 23, characters 5-12", 256, four ** four | 0);
+eq("File \"exponentiation_test.res\", line 22, characters 5-12", 0, intPow(-2147483648, 2));
+
+eq("File \"exponentiation_test.res\", line 24, characters 5-12", 256, four ** four | 0);
 
 Mt.from_pair_suites("Exponentiation_test", suites.contents);
 

tests/tests/src/exponentiation_test.res

@@ -19,6 +19,7 @@ let () = {
   eq(__LOC__, -2 ** 31, intPow(-2, 31))
   eq(__LOC__, 2 ** 32, intPow(2, 32))
   eq(__LOC__, 2147483647 ** 2, intPow(2147483647, 2))
+  eq(__LOC__, -2147483648 ** 2, intPow(-2147483648, 2))
 
   eq(__LOC__, 4 ** 4, four ** four)
 }

tests/tests/src/unified_ops_test.mjs

@@ -65,7 +65,7 @@ let pow2 = 2 ** 2;
 
 let pow3 = 2n ** 2n;
 
-let pow_overflow = 1;
+let pow_overflow = 0;
 
 let int = 3;