Add u8a <-> BN endian (#95)

packages/util/src/hex/toBn.js

@@ -9,7 +9,7 @@ const hexStripPrefix = require('./stripPrefix');
 
 /**
   @name hexToBn
-  @signature hexToBn (value?: string): BN
+  @signature hexToBn (value?: string, isLe: boolean = false): BN
   @summary Creates a BN.js bignumber object from a hex string.
   @description
     `null` inputs returns a `BN(0)` result. Hex input values return the actual value converted to a BN. Anything that is not a hex string (including the `0x` prefix) throws an error.
@@ -18,11 +18,11 @@ const hexStripPrefix = require('./stripPrefix');
 
     hexToBn('0x123480001f'); // => BN(0x123480001f)
 */
-module.exports = function hexToBn (value?: string): BN {
+module.exports = function hexToBn (value?: string, isLe: boolean = false): BN {
   // flowlint-next-line sketchy-null-string:off
   if (!value) {
     return new BN(0);
   }
 
-  return new BN(hexStripPrefix(value) || '0', 16);
+  return new BN(hexStripPrefix(value) || '0', 16, isLe ? 'le' : 'be');
 };

packages/util/src/hex/toBn.spec.js

@@ -30,4 +30,12 @@ describe('hexToBn', () => {
       )
     ).toEqual(true);
   });
+
+  it('converts little-endian', () => {
+    expect(
+      hexToBn('0x4500000000000000', true).eq(
+        new BN(69)
+      )
+    ).toEqual(true);
+  });
 });

packages/util/src/u8a/toBn.js

@@ -10,7 +10,7 @@ const u8aToHex = require('./toHex');
 
 /**
   @name u8aToBn
-  @signature u8aToHex (value?: Uint8Array): BN
+  @signature u8aToHex (value?: Uint8Array, isLe: boolean = false): BN
   @summary Creates a BN from a Uint8Array object.
   @description
     `UInt8Array` input values return the actual BN. `null` or `undefined` values returns an `0x0` value.
@@ -19,8 +19,9 @@ const u8aToHex = require('./toHex');
 
     u8aToHex(new Uint8Array([0x68, 0x65, 0x6c, 0x6c, 0xf])); // 0x68656c0f
 */
-module.exports = function u8aToBn (value?: Uint8Array): BN {
+module.exports = function u8aToBn (value?: Uint8Array, isLe: boolean = false): BN {
   return hexToBn(
-    u8aToHex(value)
+    u8aToHex(value),
+    isLe
   );
 };

packages/util/src/u8a/toBn.spec.js

@@ -13,6 +13,15 @@ describe('u8aToBn', () => {
     ).toEqual('1234');
   });
 
+  it('converts values (little-endian)', () => {
+    expect(
+      u8aToBn(
+        new Uint8Array([0x12, 0x34]),
+        true
+      ).toString(16)
+    ).toEqual('3412');
+  });
+
   it('converts empty', () => {
     expect(
       u8aToBn(