An estimate of entropy of English texts is 1.34 bits per letter [1]. This
implies that, if the letters are coded into 5 bits, one needs to
appropriately
combine 4 text files in order to obtain bit sequences of full entropy, since
4*1.34 = 5.36 > 5. The method used in our software is to sum (mod 32)
the coded
values of a-z (mapped to 0-25) as 5 bits of the corresponding letters of
the
text files.
There are plenty of other schemes for obtaining high quality pseudo-random
sequences in practice, e.g. AES in counter mode. However our scheme seems to
be much simpler both in the underlying logic (understandability) and in
implementation and is thus a viable alternative that one could use/need
under
circumstances.
The software is available at mok-kong-shen.de
M. K. Shen
------------------------------------------------------------------------
[1] T. M. Cover, R. C. King, A Convergent Gambling Estimate of the
Entropy of
English, IEEE Trans. Inf. Theory, vol. 24, 1978, pp. 413-421.
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