if {0} {
 
[LM] - 2006/02/08
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Linear Feedback Shift Registers - LFSR - 
are used as pseudo-random number generators for Cryptography and Spread Spectrum Radio applications. See [http://en.wikipedia.org/wiki/LFSR] or Bruce Schneier, "Applied Cryptography" for more information.
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Testing LFSR, we need information on runs length: 
i.e. the number of consecutive Ones or Zeroes occurring in a sequence of generated stream of bytes.
This is my solution to the problem.
 
 }
 #
 # runs_len 
 # calculates the runs lengths given a list of bytes.
 # It returns a list of runs-lengths
 #_____________________________________________________________________ 
 proc runs_len {bytelist} {
  	# Change Bytes_list into hexadecimal_string 
 	foreach b $bytelist {
 		append bstr [format "%02X" [expr {$b & 0xff}]]
 	}
 	# Change into Binary_string
 	binary scan [binary format H* $bstr] B* bits
 
 	# Runs extraction
 	set runlist [split [regsub -all {(0+|1+)} $bits "&-"] -]
 	set runlist [lreplace $runlist end end]
	
	# Runs-length list creation 
 	foreach r $runlist {
 		lappend lenlist [string length $r]
 	}
 	return $lenlist
 }

 #____________________________________________________________________
 # A simple tester
 set bytelist { 0xa6 0xb0 0x35 0xf2 0x18 0xc4}
 puts [runs_len $bytelist]



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