@polkadot/util/hex/fixLength.js

A collection of useful utilities for @polkadot

// Copyright 2017-2022 @polkadot/util authors & contributors
// SPDX-License-Identifier: Apache-2.0
import { hexAddPrefix } from "./addPrefix.js";
import { hexStripPrefix } from "./stripPrefix.js";
/**
 * @name hexFixLength
 * @summary Shifts a hex string to a specific bitLength
 * @description
 * Returns a `0x` prefixed string with the specified number of bits contained in the return value. (If bitLength is -1, length checking is not done). Values with more bits are trimmed to the specified length. Input values with less bits are returned as-is by default. When `withPadding` is set, shorter values are padded with `0`.
 * @example
 * <BR>
 *
 * ```javascript
 * import { hexFixLength } from '@polkadot/util';
 *
 * console.log('fixed', hexFixLength('0x12', 16)); // => 0x12
 * console.log('fixed', hexFixLength('0x12', 16, true)); // => 0x0012
 * console.log('fixed', hexFixLength('0x0012', 8)); // => 0x12
 * ```
 */

export function hexFixLength(value, bitLength = -1, withPadding = false) {
  const strLength = Math.ceil(bitLength / 4);
  const hexLength = strLength + 2;
  return hexAddPrefix(bitLength === -1 || value.length === hexLength || !withPadding && value.length < hexLength ? hexStripPrefix(value) : value.length > hexLength ? hexStripPrefix(value).slice(-1 * strLength) : `${'0'.repeat(strLength)}${hexStripPrefix(value)}`.slice(-1 * strLength));
}