Andor wrote:
> Jerry Avins wrote:
>> hbarcellos wrote:
>>> Hi all,
>>> I'm working whit ADSP 21161 analog devices, I'm looking for a way to
>>> generate a white noise in assembly, something like a random function
in C.
>>> kind regard's
>> A linear congruential generator is probably good enough. Thay are easy
>> to code. If you don't need all the bits, discard the lower-order
ones.http://en.wikipedia.org/wiki/Linear_congruential_generator
>
> For DSP, the linear congruential generators might be good enough.
> There is a particular pair of numbers "a" and "b", such that
>
> x(n) = (a x(n-1) + b ) % 2^32
>
> produced what looks and sounds like uniform random integers and has a
> period of 2^32 - 1. For processors that sup****t 32bit fixed-point
> arithmetic (like the SHARC), this is extremely fast (the % is for
> free). The numbers "a" and "b" are in one of Knuth's volumes and the
> old Numerical Recipes in C (in the new version, they completely
> discourage the use of linear congurential generators - a pity, because
> for dithering and simple randomization, the above generator works just
> fine).
>
> Hey wait, the old version of NR is available online here:
>
> http://www.nrbook.com/a/bookcpdf.php
>
> Chapter 7.1 (Uniform Deviates), section Quick and Dirty Generators. So
> "a" is 1664525 and "b" is 1013904223.
The link I cited gives several pairs. Knuth (TACP, chap 3) has a lot of
good discussion, but makes no specific recommendations. A general Linear
congruential RNG has the form X_{n+1} = (a*X_n + c)mod m.
For the ANSI C RNG, m=2^32, a=1103515245, c=12345, and bits 30..16 are
returned.
Jerry
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