This is an implementation of the R250 pseudo-random number generator as
an Amiga library file, random250.library. The generator is known for
it's good repetition length (10E75 numbers before it repeats) and fast
number generation speed (4 instructions for each number including the
loop overhead). This version can return either one 32 bit number or
fill an array with any number of 32 bit random numbers.
The assembler source code is included. Examples of using it in GNU C
and M2Sprint Modula-2 are also included. You can easily add it to other
languages just like you add other Amiga libraries. The two functions it
exports are:
unsigned long GenerateRandomNumber (void)
D0
/* Returns a random number in register D0. Follows the usual rules of
registers a0,a1,d0,d1 being changed while the rest are preserved,
assumes a6 points to the library base you got from calling
OpenLibrary ("random250.library", 0). The library offset for this
function is -30 (decimal). */
void GenerateRandomArray (unsigned long N, unsigned long *Array)
D0 A0
/* Fills the given array with N random numbers, each taking 4 bytes,
so it fills 4*N bytes. N in D0, array start address in A0.
Library offset -36. */
Because it is in a library, it handles initialisation automatically
(using the current date and time, state of the Exec variables and some
other stuff to seed the generator) when opened. It has semaphores
guarding its global seed variable so that multiple programs can use it
simultaneously. Unfortunately, this means that there is a lot of
overhead for getting just one random number. Instead of calling it for
each number, you should use the function that fills an array with random
numbers.
Random250.library is released to the public domain. That means you can
hack it up. Or just strip out the code and include it in your own
program directly for extra speed. That also means I'm not responsible
for it running amuck. But if you do find bugs, please let me know
because I'm using it for certain other things (like skip lists).
- Alex
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