Adjust encoder/decoder fallbacks (#750)

* Adjust encoder/decoder fallbacks

* Dep-dup is functions

* Complexity cleanups

packages/x-randomvalues/src/fallback.spec.ts

@@ -0,0 +1,20 @@
+// Copyright 2017-2020 @polkadot/x-randomvalues authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+import fallback from './fallback';
+
+describe('fallback (insecure)', (): void => {
+  it('subsequent results does not match', (): void => {
+    expect(
+      fallback(new Uint8Array(32)).toString()
+    ).not.toEqual(
+      fallback(new Uint8Array(32)).toString()
+    );
+  });
+
+  it('generates with the supplied length', (): void => {
+    expect(
+      fallback(new Uint8Array(128))
+    ).toHaveLength(128);
+  });
+});

packages/x-randomvalues/src/fallback.ts

@@ -16,11 +16,11 @@ export default function insecureRandomValues <T extends Uint8Array> (arr: T): T
   let r = 0;
 
   for (let i = 0; i < arr.length; i++) {
-    if ((i & 0x03) === 0) {
+    if ((i & 0b11) === 0) {
       r = Math.random() * 0x100000000;
     }
 
-    arr[i] = (r >>> ((i & 0x03) << 3)) & 0xff;
+    arr[i] = (r >>> ((i & 0b11) << 3)) & 0xff;
   }
 
   return arr;

packages/x-randomvalues/src/react-native.ts

@@ -16,9 +16,6 @@ interface RNExt {
 }
 
 function getRandomValuesNative <T extends Uint8Array> (arr: T): T {
-  // We may want to use a base64 decoder here, but we certainly have an issue where we
-  // want/need this part as lean as possible. Since Buffer is already needed elsewhere
-  // (an generally prevalent in JS), we rather use it as-is.
   return Buffer
     .from((NativeModules as RNExt).RNGetRandomValues.getRandomBase64(arr.length), 'base64')
     .reduce((arr, byte, index): T => {