Do you know your bitwise operators? • Hacker News Board

Re: Do you know your bitwise operators?

#11

Post by dalke » Fri, Jan 10, 2014, 7:56 PM UTC

sp332 wrote: post #9

dalke wrote: post #8

Earlier quoted context omitted.

It appears to have a limited JS validator to prevent you from using anything other than the limited operators it allows.

It really doesn't like having anything after "return" except a single value or variable.

That's not it. For example, it accepts "return x|x&x;" . The restriction is that only a handful of Javascript operations are allowed. Anything else gives a hard-to-understand error message.

Re: Do you know your bitwise operators?

#12

Post by sachleen » Fri, Jan 10, 2014, 8:00 PM UTC

warmfuzzykitten wrote: post #2

Validator seems broken.

Definitely.

  function one_bit(x) {
    return 1
  }

  Solution did not return correct output for x=1. Expected output: 1, got: 0

umm... ok

Re: Do you know your bitwise operators?

#13

Post by wellingtons » Fri, Jan 10, 2014, 8:03 PM UTC

conductr wrote: post #4

This is stated to be a puzzle. But, when does this actually get used? Are there use cases of bit manipulation in JS? I've never understood when using bit operators could be necessary or even useful. Of course, I'm speaking from my experience building web apps; ruby, python, js, php, etc. I don't have much other programming experience

To do this exercise in javascript is pretty silly. But as a systems developer, I can tell you that bit manipulation happens all over the place in my line of work.

Re: Do you know your bitwise operators?

#14

Post by wellingtons » Fri, Jan 10, 2014, 8:04 PM UTC

fourspace wrote: post #6

warmfuzzykitten wrote: post #2

Validator seems broken.

I certainly can't get it to work. For the first problem, I tried: function one_bit(x) { return x & (x-1) == 0 } Only to see this error: Expected "}" or comment but "&" found. WAT

You can't use '-'.

Re: Do you know your bitwise operators?

#15

Post by blt » Fri, Jan 10, 2014, 8:06 PM UTC

conductr wrote: post #4

This is stated to be a puzzle. But, when does this actually get used? Are there use cases of bit manipulation in JS? I've never understood when using bit operators could be necessary or even useful. Of course, I'm speaking from my experience building web apps; ruby, python, js, php, etc. I don't have much other programming experience

- Packing lots of small pieces of information into a single memory word - for example, 3-3-2 bit RGB [1]

- Interacting with hardware that uses certain bits in a register to control behavior - for example, Arduino digital ports [2]

- Doing arithmetic extra-fast with numbers that are powers of two - modulo becomes bitwise-and, division and multiplication become shifts

[1] http://en.wikipedia.org/wiki/List_of_monochrome_and_RGB_pale...

[2] http://arduino.cc/en/Reference/PortManipulation

Re: Do you know your bitwise operators?

#16

Post by 10098 » Fri, Jan 10, 2014, 8:14 PM UTC

The validator doesn't work at all.

Re: Do you know your bitwise operators?

#17

Post by 10098 » Fri, Jan 10, 2014, 8:20 PM UTC

conductr wrote: post #4

This is stated to be a puzzle. But, when does this actually get used? Are there use cases of bit manipulation in JS? I've never understood when using bit operators could be necessary or even useful. Of course, I'm speaking from my experience building web apps; ruby, python, js, php, etc. I don't have much other programming experience

This is mostly done in lower level code, so no wonder you have never bumped into it. One easy example, though is passing a set of binary options around, which is useful, for example, when you want to say "enable those features, and disable those other features". You can pack up to 32 options into a 4-byte integer.

Re: Do you know your bitwise operators?

#18

Post by amenghra » Fri, Jan 10, 2014, 8:29 PM UTC

warmfuzzykitten wrote: post #2

Validator seems broken.

:(

Oops, i'll fix it.

Re: Do you know your bitwise operators?

#19

Post by amenghra » Fri, Jan 10, 2014, 8:31 PM UTC

conductr wrote: post #4

This is stated to be a puzzle. But, when does this actually get used? Are there use cases of bit manipulation in JS? I've never understood when using bit operators could be necessary or even useful. Of course, I'm speaking from my experience building web apps; ruby, python, js, php, etc. I don't have much other programming experience

real world application: https://github.com/facebook/hhvm/blob/master/hphp/compiler/a...

Re: Do you know your bitwise operators?

#20

Post by amenghra » Fri, Jan 10, 2014, 8:32 PM UTC

wellingtons wrote: post #13

conductr wrote: post #4

This is stated to be a puzzle. But, when does this actually get used? Are there use cases of bit manipulation in JS? I've never understood when using bit operators could be necessary or even useful. Of course, I'm speaking from my experience building web apps; ruby, python, js, php, etc. I don't have much other programming experience

To do this exercise in javascript is pretty silly. But as a systems developer, I can tell you that bit manipulation happens all over the place in my line of work.

There is nothing inherently javascript about this, besides providing a UI to validate the answer (that's when the validator works...)