add restriction to avoid Math.imul

Author: cometkim

text/0001-int.md

@@ -66,20 +66,38 @@ The [`ToInt32`] behavior follows the definition in ECMA-262 as is. In action, th
 1. Let `number` be mathmatically $x * y$.
 2. Let `int32` be `fromNumber(number)`, return `int32`.
 
+The `multiply(x, y)` must produce the same result as `add(x)` accumulated `y` times.
+
+```res
+let multiply = (x, y) => {
+  let id = 0
+  let rec multiply = (x, y, acc) => {
+    switch y {
+    | 0 => acc
+    | n => multiply(x, n - 1, add(x, acc))
+    }
+  }
+  multiply(x, y, id)
+}
+```
+
 ### `exponentiate(x, y)`
 
 1. Let `number` be mathmatically $x ^ y$.
 2. Let `int32` be `fromNumber(number)`, return `int32`.
 
-`exponentiate(x, y)` must match the result of `multiply` accumulated `y` times.
+The `exponentiate(x, y)` must produce the same result as `multiply(x)` accumulated `y` times.
 
-```js
-function exponentiate(x, y) {
-  let int32 = 1;
-  for (let i = 0; i < y; i++) {
-    int32 *= x;
+```res
+let exponentiate = (x, y) => {
+  let id = 1
+  let rec exponentiate = (x, y, acc) => {
+    switch y {
+    | 0 => acc
+    | n => exponentiate(x, n - 1, multiply(x, acc))
+    }
   }
-  return int32 | 0;
+  exponentiate(x, y, id)
 }
 ```