Hello everybody.
I've seen there's some interest in generating (pseudo-)random numbers.
For those like me that don't have Java in the server, maybe something
could be done with a simple RNG, like Marsaglia's "Mother-of-All".
I don't know about XPath number formats, if the necessary functions
exist or its efficiency, but here is the info:
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[ from http://www.agner.org/random/mother/ ]
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Algorithm: S = 2111111111 · Xn-4 + 1492 · Xn-3 + 1776 · Xn-2
+ 5115 · Xn-1 + C
Xn = S modulo 2^32
C = floor(S / 2^32)
The last four X'es and C are stored in a buffer as 32-bit unsigned
integers. The intermediate S is a 64-bit unsigned integer.
The X'es and C are initialized to random values based on a seed. They
cannot all be zero.
This algorithm is most effectively implemented in assembly language
where you have an instruction for multiplying two 32-bit integers and
get a 64-bit product. In high level languages you do not have such an
instruction, so you have to use floating point numbers with a mantissa
of at least 63 bits. Not all compilers support this precision, for
example Microsoft Visual C++ does not.
Specifications:
32-bit integer output
cycle length is 3·10^47
very good randomness
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Anyone dares to make an XSLT/XPath version? :)
Saludos,
Antonio
http://www.webcsd.com
mailto:atnbueno@xxxxxxxxxx
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