rand() function performs poorly

William M. Grim wgrim at siue.edu
Wed May 12 00:42:35 PDT 2004

Matthew Dillon wrote:
:When you run that code, it will print "OoOoOoOo..." without any change; 
:it's very predictable.
:I'm certainly up for bringing the later 4.x rand() code down into 
:DragonFly.  Where do you think they keep it?
:And don't one of you other peeps go and do it for me. :-D  I want to try 
:this one on my own!  >:-)

    I think you are talking about /usr/src/lib/libc/stdlib/rand.c, but
    I don't think FreeBSD-4 or FreeBSD-5 has fixed that.  They committed
    something but it looks like they backed it out.
    Most people use the random()/srandom() facility rather then the old
    rand() facility, or use /dev/urandom.  The old rand() facility 
    is severely limited due to API requirements and constraints.

					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>
You could be right.  I am attempting to update my dfly before I go 
searching for the fixes FreeBSD has.  However, I am assuming it was 
"fixed" in some way, because on FreeBSD 5.2.1, the output comes out more 
random, such as "OOooooOOoOOOOOOoo..." or something.

On (at least) FreeBSD 4.8, the output comes out in a similar way 
(according to my friend who ran the test for me on that system).

I never actually read "man 3 rand" on DFly/FBSD because I knew how it 
worked from books I have.  However, I now notice the first line is 
"These interfaces are obsoleted by random(3)."  Regardless of this 
though, I think it might be worth me patching it with FreeBSD's fix 
since I'm sure several people use this function in older code, including me.

What do you think?


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