feat: add RANGE_CHECK builtins (#19)

* added RANGE_CHECK function

* changed initialization format of RC_BOUND bigint

* add comment

* rebased latest updates, refacto, added custom function in Code.ts file

src/builtins/range_check/range_check.ts

@@ -0,0 +1,10 @@
+const RC_BOUND: bigint = BigInt(2 ** 128);
+
+// performs a range check for the input num of type bigint.
+function range_check(num: bigint): bigint {
+  if (num < RC_BOUND) {
+    return num;
+  } else {
+    throw new InvalidRangeError();
+  }
+}

src/ui/Code.ts

@@ -103,6 +103,7 @@ function BITWISE_XOR(x: number, y: number): bigint {
  */
 function BITWISE_OR(x: number, y: number): bigint {
   return bitwise_or(BigInt(x), BigInt(y));
+}
 
 function EC_OP(
   m: number | string,
@@ -111,3 +112,14 @@ function EC_OP(
 ): AffinePoint {
   return ec_op(BigInt(m), p, q);
 }
+
+/**
+ * Provides custom function for range checking a given input.
+ *
+ * @param {number} num - The number which is to be validated.
+ * @return The number itself in bigint form if it is in range, else throws InvalidRangeError.
+ * @customfunction
+ */
+function RANGE_CHECK(num: number): bigint {
+  return range_check(BigInt(num));
+}

src/vm/errors.ts

@@ -6,4 +6,5 @@ class InvalidApUpdateError extends Error {}
 class InvalidOp0RegisterError extends Error {}
 class InvalidOp1RegisterError extends Error {}
 class InvalidDstRegisterError extends Error {}
+class InvalidRangeError extends Error {}
 class AssertEqError extends Error {}