5 ms·

Every random() function is kind of deterministic, but still very interesting discovery!

by kmbriedis 9y ago

TomAnthony 9y ago
Yeah, as was pointed out in /r/programming, it is perhaps an imperfect title in hindsight!
- KyeRussell 9y ago
  Technically true, but pointless pedantry when I'm sure that most people are on the the same page wrt pseudorandomness. Typically what I'd expect of /r/programming.
skrebbel 9y ago
Totally down nitpick alley yeah, but: Not if fed by an external source of randomness (eg cosmic rays).
- philbarr 9y ago
  > (eg cosmic rays). YouTube copyright violations? The chance of getting a response from Google support?
  - skrebbel 9y ago
    I love those. A bit easy to game if you have the right job at Google, but still this is cool. I'd also assume that the Twitter firehose could be a great source of randomness.
- Godel_unicode 9y ago
  Since we're nitpicking; deterministic effectively means same input produces same output. Input includes the seed. All PRNGs are deterministic.
  - squeaky-clean 9y ago
    Javascript does not allow you to set the seed for the default PRNG. So for our purposes it's essentially non-deterministic. You need to use a custom library if you want to be able to specify your seed.
    - Godel_unicode 9y ago
      Continuing the nitpicking: "JavaScript" isn't actually what prevents setting the seed, you're talking about a common implementation detail of specific JavaScript runtimes (Mozilla’s documentation says their seed can't be changed, for instance). A runtime developer could, as Googlebot apparently does, seed the prng with a constant value. You could also use some user-provided constant as the seed. All three are compliant with the letter of the spec. Bottom line: the PRNG is, as all PRNGs are, deterministic. The user-facing math.random API using the underlying PRNG may or may not be. Those are distinct things. From the spec's description of math.random with regard to random or pseudo-random: "...using an implementation‑ dependent algorithm or strategy."

Every random() function is kind of deterministic, but still very interesting discovery!

TomAnthony 9y ago

Yeah, as was pointed out in /r/programming, it is perhaps an imperfect title in hindsight!

KyeRussell 9y ago
Technically true, but pointless pedantry when I'm sure that most people are on the the same page wrt pseudorandomness. Typically what I'd expect of /r/programming.

skrebbel 9y ago

Totally down nitpick alley yeah, but: Not if fed by an external source of randomness (eg cosmic rays).

philbarr 9y ago
> (eg cosmic rays). YouTube copyright violations? The chance of getting a response from Google support?
- skrebbel 9y ago
  I love those. A bit easy to game if you have the right job at Google, but still this is cool. I'd also assume that the Twitter firehose could be a great source of randomness.
Godel_unicode 9y ago
Since we're nitpicking; deterministic effectively means same input produces same output. Input includes the seed. All PRNGs are deterministic.
- squeaky-clean 9y ago
  Javascript does not allow you to set the seed for the default PRNG. So for our purposes it's essentially non-deterministic. You need to use a custom library if you want to be able to specify your seed.
  - Godel_unicode 9y ago
    Continuing the nitpicking: "JavaScript" isn't actually what prevents setting the seed, you're talking about a common implementation detail of specific JavaScript runtimes (Mozilla’s documentation says their seed can't be changed, for instance). A runtime developer could, as Googlebot apparently does, seed the prng with a constant value. You could also use some user-provided constant as the seed. All three are compliant with the letter of the spec. Bottom line: the PRNG is, as all PRNGs are, deterministic. The user-facing math.random API using the underlying PRNG may or may not be. Those are distinct things. From the spec's description of math.random with regard to random or pseudo-random: "...using an implementation‑ dependent algorithm or strategy."