Alternative to bitwise operators in uuid creation

Question

I'm using the following typescript method to generate UUIDs. The code itself is basically the typescript version of this stackoverflow answer.

generateUUID(): string {
    let date = new Date().getTime();
    if (window.performance && typeof window.performance.now === 'function') {
        date += performance.now();
    }
    let uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
        let r = (date + Math.random() * 16) % 16 | 0;
        date = Math.floor(date / 16);
        return (c === 'x' ? r : (r & 0x3 | 0x8)).toString(16);
    });
    return uuid;
};

Our development team uses TSLint to keep the code clean and we have a rule that forbids to use bitwise operators. I have no idea how to rewrite this code without harming the cryptographic aspect of the UUID generator. How can this piece of code be rewritten or doesn't this make sense at all?

Why on earth do you have a rule that forbids bitwise operators? That's weird. — Pointy, Dec 19 '16 at 13:46
Wrap it in: `/* tslint:disable */` and `/* tslint:enable */` (Or be more specific about the rule we are "accepting", see https://palantir.github.io/tslint/usage/rule-flags/ ) — Matthew Wilcoxson, Dec 19 '16 at 13:48
To add a bit of background: The use of bitwise operators is often discouraged in javascript because they can be confused with logical operators. Consider `1 && 1 === 1` and `1 & 1 === 0`. — jobB, Dec 19 '16 at 13:54
@jobB I think it is a good practive to forbid those bitwise operators because someone could really forget a character of some logical operator. It might seem best to deactivate the rule for the uuid code though? — Sebastian Krogull, Dec 19 '16 at 14:00

Matthew Wilcoxson · Accepted Answer · 2018-04-04T17:20:01.220

19

The reason TSLint highlights this is because it is more likely the bitwise operator has been used accidentally (for instance, in an if statement) than to have used it on purpose.

It should be quite acceptable to tell TSLint that you really meant to use a bitwise operator. Just wrap them in special TSLint comments. :

/* tslint:disable:no-bitwise */

// Your code...

/* tslint:enable:no-bitwise */

edited Apr 04 '18 at 17:20

answered Dec 19 '16 at 14:00

Matthew Wilcoxson

3,432
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3

you can put this comment just for the next line: // tslint:disable-next-line:no-bitwise – Jeffrey Nicholson Carré Jul 13 '19 at 05:25

score 1 · Answer 2 · answered Dec 18 '18 at 20:08

export abstract class SystemGuid{
    constructor() {
      // no-op
    }
    public static UUID(): string {
      if (typeof window !== 'undefined' && typeof window.crypto !== 'undefined' 
      && typeof window.crypto.getRandomValues !== 'undefined') {
        const buf: Uint16Array = new Uint16Array(8);
        window.crypto.getRandomValues(buf);
        return (
          this.pad4(buf[0]) +
          this.pad4(buf[1]) +
          '-' +
          this.pad4(buf[2]) +
          '-' +
          this.pad4(buf[3]) +
          '-' +
          this.pad4(buf[4]) +
          '-' +
          this.pad4(buf[5]) +
          this.pad4(buf[6]) +
          this.pad4(buf[7])
        );
      } else {
        return (
          this.random4() +
          this.random4() +
          '-' +
          this.random4() +
          '-' +
          this.random4() +
          '-' +
          this.random4() +
          '-' +
          this.random4() +
          this.random4() +
          this.random4()
        );
      }
    }
    private static pad4(num: number): string {
      let ret: string = num.toString(16);
      while (ret.length < 4) {
        ret = '0' + ret;
      }
      return ret;
    }
    private static random4(): string {
      return Math.floor((1 + Math.random()) * 0x10000)
        .toString(16)
        .substring(1);
    }
    public static generate(): string {
      return SystemGuid.UUID();
    }
   }

Alternative to bitwise operators in uuid creation

2 Answers2