10-07-2009
Quote:
Originally Posted by
jim mcnamara
Do not reseed. Otherwise you keep getting the same value.
PNG's are setup to generate a series of random numbers from a single starting point. Reseeding before every call to rand() "undoes" that. IT does NOT randomize better.
...but he
should seed *once* -- or he'll get the same numbers anyway. I take "running 30 times per second" to mean 30 processes per second, and each process must seed once to get different numbers.
Yes, you can get seconds and microseconds from
gettimeofday().
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LEARN ABOUT MOJAVE
urandom
RANDOM(4) BSD Kernel Interfaces Manual RANDOM(4)
NAME
random , urandom -- random data source devices.
SYNOPSIS
pseudo-device random
DESCRIPTION
The random device produces uniformly distributed random byte values of potentially high quality.
To obtain random bytes, open /dev/random for reading and read from it.
The same random data is also available from getentropy(2). Using the getentropy(2) system call interface will provide resiliency to file
descriptor exhaustion, chroot, or sandboxing which can make /dev/random unavailable. Additionally, the arc4random(3) API provides a fast
userspace random number generator built on the random data source and is preferred over directly accessing the system's random device.
/dev/urandom is a compatibility nod to Linux. On Linux, /dev/urandom will produce lower quality output if the entropy pool drains, while
/dev/random will prefer to block and wait for additional entropy to be collected. With Yarrow, this choice and distinction is not necessary,
and the two devices behave identically. You may use either.
The random device implements the Yarrow pseudo random number generator algorithm and maintains its entropy pool. The kernel automatically
seeds the algorithm with additional entropy during normal execution.
FILES
/dev/random
/dev/urandom
HISTORY
A random device appeared in the Linux operating system.
Darwin September 6, 2001 Darwin