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 — set_random_source [2006/09/19 03:45] (current) Line 1: Line 1: + ======Synopsis:​====== + [[set]] random_source [<​0|1|2|3>​] + + ======Description:​====== + The [[rand]]om function generates random numbers. ​ But what is a random + number? ​ A random number generator is often measured by 3 attributes + + | Entropy | Given a set of the last random numbers, how likely is it you can guess the next random number? (High entropy means less guessability) | + | Distribution | Given a set of the last random numbers, how likely is it each of the possible values of have appeared the same number of times? (High distribution means every value is hit the same number of times) | + | Repeatability | Given a set of the first random numbers, how likely is it that you can create the same random numbers again? (High repeatability means you can regenerate the same sequence upon request) | + + A discussion of the pros and cons of each of these attributes is beyond + the scope of this document. ​ But the client has 4 random number generators: + + ^ Value ^ Description ^ Entropy ^ Distribution ^ Repeatability ^ + | 0 | Reads from /​dev/​urandom | High | Medium | No | + | 1 | Traditional ircII PRNG | Low | High | Yes | + | 2 | gettimeofday() calls | Medium | Low | No | + | 3 | arc4random PRNG | High | Medium | No | + + The factory default value is 0.  Although you can [[set]] the value to + other than 0, 1, 2, or 3, any other values are treated as though you had + set it to 3.  If /​dev/​urandom is not available, then 0 behaves as though + you had set it to 1. + + The random number generator is used by [[rand]] and [[randread]] + + ======History:​====== + The [[set random_source]] variable first appeared in EPIC4pre2.001-NR13. + Arc4random support (set random_source 3) first appeared in EPIC4-1.1.8. + + #\$EPIC: set_random_source.txt,​v 1.5 2006/09/19 03:45:37 jnelson Exp \$