feat: adding protobuf decoder for parse of google auth migrations

lib/protobuf-decoder/intUtils.js

@@ -0,0 +1,27 @@
+import JSBI from "jsbi";
+
+export function interpretAsSignedType(n) {
+  // see https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/wire_format_lite.h#L857-L876
+  // however, this is a simpler equivalent formula
+  const isEven = JSBI.equal(JSBI.bitwiseAnd(n, JSBI.BigInt(1)), JSBI.BigInt(0));
+  if (isEven) {
+    return JSBI.divide(n, JSBI.BigInt(2));
+  } else {
+    return JSBI.multiply(
+      JSBI.BigInt(-1),
+      JSBI.divide(JSBI.add(n, JSBI.BigInt(1)), JSBI.BigInt(2))
+    );
+  }
+}
+
+export function interpretAsTwosComplement(n, bits) {
+  const isTwosComplement = JSBI.equal(
+    JSBI.signedRightShift(n, JSBI.BigInt(bits - 1)),
+    JSBI.BigInt(1)
+  );
+  if (isTwosComplement) {
+    return JSBI.subtract(n, JSBI.leftShift(JSBI.BigInt(1), JSBI.BigInt(bits)));
+  } else {
+    return n;
+  }
+}