Usage: ent16 [-%nn]
Computes an estimate of the entropy of stdin.
If the flag '-%75' is given (e.g.), then the
  exit status is 1 only if the input could be
  compressed at least 75%, otherwise the exit
  status is 0.  Legal values of 'nn' are 1..99.
In any case, the entropy and compression estimates
  are printed to stdout, even if no '-%nn' flag is.

METHOD: entropy is estimated by building a histogram
        of all 16 bit words in the input, then summing
        over -p[i]*log2(p[i]), i=0..65535.  Compression
        estimate seems to work pretty good for gzip -1
        in most cases of binary image data.

SAMPLE USAGE (csh syntax):
  ent16 -%75 < fred+orig.BRIK