diff options
Diffstat (limited to 'lib/libc/stdlib/random.3')
| -rw-r--r-- | lib/libc/stdlib/random.3 | 42 |
1 files changed, 29 insertions, 13 deletions
diff --git a/lib/libc/stdlib/random.3 b/lib/libc/stdlib/random.3 index 84680e2..dd85711 100644 --- a/lib/libc/stdlib/random.3 +++ b/lib/libc/stdlib/random.3 @@ -64,11 +64,16 @@ The period of this random number generator is very large, approximately .if n 16*((2**31)\(mi1). .Pp The -.Fn random Ns / Fn srandom -have (almost) the same calling sequence and initialization properties as -.Xr rand 3 Ns / Xr srand 3 . +.Fn random +and +.Fn srandom +functions have (almost) the same calling sequence and initialization properties as the +.Xr rand 3 +and +.Xr srand 3 +functions. The difference is that -.Xr rand +.Xr rand 3 produces a much less random sequence \(em in fact, the low dozen bits generated by rand go through a cyclic pattern. All the bits generated by .Fn random @@ -77,15 +82,8 @@ are usable. For example, will produce a random binary value. .Pp -Unlike -.Xr srand , -.Fn srandom -does not return the old seed; the reason for this is that the amount of -state information used is much more than a single word. (Two other -routines are provided to deal with restarting/changing random -number generators). Like +Like .Xr rand 3 , -however, .Fn random will by default produce a sequence of numbers that can be duplicated by calling @@ -156,11 +154,29 @@ is called with less than 8 bytes of state information, or if detects that the state information has been garbled, error messages are printed on the standard error output. .Sh SEE ALSO -.Xr rand 3 +.Xr rand 3 , +.Xr srand 3 .Sh HISTORY These functions appeared in .Bx 4.2 . .Sh BUGS +.Pp About 2/3 the speed of .Xr rand 3 . +.Pp +The historical implementation used to have a very weak seeding; the +random sequence did not vary much with the seed. For compatibility +reasons, this implementation has been made available until the +next FreeBSD release +via the +functions +.Fn orandom , +.Fn osrandom , +.Fn oinitstate +and +.Fn osetstate +from the compatibility library, +.Em libcompat . +The current implementation employs a better pseudo-random number +generator for the initial state calculation. |
