Talk:Clock drift

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[edit] Code example

The example of "pseudo code" is not, I would suggest, psuedo code. It is more like actual code. I can't tell which language it's from, but it's not that easy to follow if you don't know the particular language. It should be re-cast as true pseudo code. Arcturus 10:40, 29 July 2006 (UTC)

Well, this is Wikipedia. Be bold and fix it! Don't ask others to fix it. And yes, I just typed down the first code that came to mind and focused more on correctness of that code than making it very easy to read. We should probably change the C-style for-loop to a while loop or even plain english or so, as I did with the inner loop. In my first version that inner loop too was a C-style for-loop. I was thinking of writing a description in plain english too, and having the "pseudocode" look more like actual code as it does now. So I think there are several ways to go: Either have a very easy to read pseudocode, or have plain english + a code example in for instance C or perhaps just a code example in C but with very good comments? I haven't done either yet since I need to think about it for some days.

Besides, in a real system we usually do not do the modulo 256 since that would be a waste since the higher bits also contain some randomness. (Especially in the first round since that varies from zero to "average loop value" due to the first round starting anywhere in the middle of a tick.) Instead usually we put the full 32-bit loop values in the array and when finished we hash the whole array down to one 256-bit value. Note that the hash method used need not be a secure one, any "compression function" with a good avalanche effect is good enough. Hash functions just happens to be such compression functions. But I wanted to keep the example as easy as possible so I used modulo instead of hashing.

So there are some thinking and discussion to do about how to best show how to do clock drift measuring.

--David Göthberg 17:29, 29 July 2006 (UTC)

Since someone removed the pseudocode from the article here it is for reference:

The pseudocode below shows a "software random number generator" that produces 256 random bits and that loads the CPU fully for about 1/3 of a second. This assumes the system tick is 100 times per second and a fairly fast modern computer where the number of loops per tick will be high so each loop will vary with at least 8 bits worth of randomness. The measurement is done 32 times (during 32 separate ticks), each time producing 8 bits of randomness.

(* Code for a software random number generator. *)

var  RNGarray: array[0..31] of byte;   (* An array of 32 bytes. *)

(* Do 32 clock drift measurements. *)
for x := 0 to 31 do begin

  tick := clock();

  (* Count loops until the next tick. *)
  loop := 0;
  while clock() = tick do begin
    loop := loop + 1
  end; (* tick loop *)

  (* Use the lower 8 bits since those are the ones that vary wildly. *)
  RNGarray[x] := loop modulo 256

end (* index loop *)

(* The RNGarray now contains 256 random bits. *)

--David Göthberg 13:01, 23 June 2007 (UTC)

[edit] Atomic clock drift due to realitivity

I'd like to see some actual data regarding the speed in which the various cessium clocks placed around the globe have been in motion. The argument that "the atomic clocks drift, and they're in motion because they're on earth. Ergo it's the cause is realitivistic time dialation" is simply not enough for me. I want to see a citation of actual test data and how it all coincides with the math behind realitivity. I'm tempted to remove the realitivity section, but I respect Einstein's theories enough to give them the benefit of the doubt. But it pains me to see the cause of physics anamolies being "a wizard did it" and Einsteins theories being cited as "the wizard who did it" without any testing of any sort. I almost feel like the realitivity section amounts to someone with frazzled hair dressed up in a lab coat and welding goggles, pointing dramatically at cessium clocks and shouting "SCIENCE!" with that being all the justification the section needs. 24.254.163.150 (talk) 07:59, 8 January 2008 (UTC)

[edit] merge

I suggest merging the section hardware_random_number_generator#Clock_drift into the section clock_drift#Random_number_generators. Both are talking about the same thing, a hardware random number generator based on two or more independent oscillators. I suspect that afterward the merge, we might find we have enough material to split out that section into its own article. What do you think about merging? If we make a new article from that material, what should we call it? "clock drift random number generator" ? "oscillator driven random number generator" ? --68.0.124.33 (talk) 20:23, 5 April 2008 (UTC)