@0x/contracts-test-utils: Allow hexSlice() to take negative numbers, and a range.

contracts/test-utils/CHANGELOG.json

@@ -81,6 +81,10 @@
             {
                 "note": "Add `Numberish` type.",
                 "pr": 2131
+            },
+            {
+                "note": "Tweaks/Upgrades to `hex_utils`, most notably `hexSlice()`",
+                "pr": "TODO"
             }
         ]
     },

contracts/test-utils/src/hex_utils.ts

@@ -3,6 +3,7 @@ import * as crypto from 'crypto';
 import * as ethUtil from 'ethereumjs-util';
 
 import { constants } from './constants';
+import { Numberish } from './types';
 
 const { WORD_LENGTH } = constants;
 const WORD_CEIL = new BigNumber(2).pow(WORD_LENGTH * 8);
@@ -24,39 +25,44 @@ export function hexRandom(size: number = WORD_LENGTH): string {
 /**
  * Left-pad a hex number to a number of bytes.
  */
-export function hexLeftPad(n: string | BigNumber | number, size: number = WORD_LENGTH): string {
+export function hexLeftPad(n: Numberish, size: number = WORD_LENGTH): string {
     return ethUtil.bufferToHex(ethUtil.setLengthLeft(toHex(n), size));
 }
 
 /**
  * Right-pad a hex number to a number of bytes.
  */
-export function hexRightPad(n: string | BigNumber | number, size: number = WORD_LENGTH): string {
+export function hexRightPad(n: Numberish, size: number = WORD_LENGTH): string {
     return ethUtil.bufferToHex(ethUtil.setLengthRight(toHex(n), size));
 }
 
 /**
  * Inverts a hex word.
  */
-export function hexInvert(n: string | BigNumber | number, size: number = WORD_LENGTH): string {
+export function hexInvert(n: Numberish, size: number = WORD_LENGTH): string {
     const buf = ethUtil.setLengthLeft(toHex(n), size);
     // tslint:disable-next-line: no-bitwise
     return ethUtil.bufferToHex(Buffer.from(buf.map(b => ~b)));
 }
 
 /**
- * Slices off the desired number of bytes from a hex number.
+ * Slices a hex number.
  */
-export function hexSlice(n: string | BigNumber | number, size: number): string {
+export function hexSlice(n: Numberish, start: number, end?: number): string {
-    const hex = toHex(n);
+    const hex = toHex(n).substr(2);
-    return '0x'.concat(toHex(n).slice(size * 2 + 2, hex.length));
+    const sliceStart = start >= 0 ? start * 2 : Math.max(0, hex.length + start * 2);
+    let sliceEnd = hex.length;
+    if (end !== undefined) {
+        sliceEnd = end >= 0 ? end * 2 : Math.max(0, hex.length + end * 2);
+    }
+    return '0x'.concat(hex.substring(sliceStart, sliceEnd));
 }
 
 /**
  * Convert a string, a number, or a BigNumber into a hex string.
  * Works with negative numbers, as well.
  */
-export function toHex(n: string | BigNumber | number, size: number = WORD_LENGTH): string {
+export function toHex(n: Numberish, size: number = WORD_LENGTH): string {
     if (typeof n === 'string' && /^0x[0-9a-f]+$/i.test(n)) {
         // Already a hex.
         return n;
@@ -64,7 +70,14 @@ export function toHex(n: string | BigNumber | number, size: number = WORD_LENGTH
     let _n = new BigNumber(n);
     if (_n.isNegative()) {
         // Perform two's-complement.
-        _n = new BigNumber(hexInvert(toHex(_n.abs()), size).substr(2), 16).plus(1).mod(WORD_CEIL);
+        // prettier-ignore
+        _n = new BigNumber(
+            hexInvert(
+                toHex(_n.abs()),
+                size,
+            ).substr(2),
+            16,
+        ).plus(1).mod(WORD_CEIL);
     }
     return `0x${_n.toString(16)}`;
 }