generating random numbers in C - Page 2

tuxdev · 11-05-2009, 09:52 PM

640K is enough for anybody.

bartonski · 11-06-2009, 01:53 AM

Quote:

Originally Posted by smeezekitty

how can you even call a program 1000000 times per second?
bash, batch and C system and exec calls are all too slow.
the only way you could do it is if its from withen it self and in that case it would have the same PID.

If you XOR the PID, you don't have to use that type of time resolution.

I can't tell you why, but I like

Code:

seed ( getpid() ^ time() );

better than

Code:

seed( tv_sec * tv_usec (microseconds));

Moore's law ought to knock about 3 orders of magnitude off your safety factor there in 10 years, or 6 in 20. The first line of code will work just as well then as now. The second? I'll take your bet that I can't launch processes that fast in 10 years.

graemef · 11-06-2009, 03:31 AM

Having looked through the thread it would appear that the answer I was going to give to the original problem has already been given by Johnsfine.

However, the digression on how you seed the random numbers raises a few thoughts. To me I don't like the idea of using the PID because first it is not cross platform. I also like to keep a record of the seed so that the process can be recreated so I tend not to use time() either rather a variable that could be read in or derived (possibly from the time function). But basically if having "random numbers" is a critical element of a program then don't use the rand function but look for a means of getting true random numbers.

Wim Sturkenboom · 11-06-2009, 03:39 AM

Quote:

Having looked through the thread it would appear that the answer I was going to give to the original problem has already been given by Johnsfine.

johnsfine was a little late

This thread was started 4 years ago

johnsfine · 11-06-2009, 08:48 AM

Quote:

Originally Posted by Wim Sturkenboom

johnsfine was a little late

This thread was started 4 years ago

Oops!

I didn't notice the fact that the thread was reopened with a different question, nor the dates on the earlier posts. I just saw that there seemed to be no answer posted for the original question.

I really wish the forum software would give some very visible indication when there is a giant jump in date between two successive posts in a thread.