part 21 encode/decode binary

gistfile1.groovy

//my version of http://groovyconsole.appspot.com/script/646001
def in_bin = ["0", "1", "111011", "100100101010", "001101", "01000" ]
def p21_rep = []  //in_bin encoded in part 21 format
def d = []        //extra binary digits in p21_rep
def hex = []      //hex part of p21_rep
def nibbles = []  //number of hex digits
def out_bin = []  //p21_rep decoded
def num_bits = [] //number of used bits
def zeros = []    //number of binary zeros to prepend to out_bin
def padded = []   //num_bits + d
//encode
in_bin.each { value ->
 def i = Integer.parseInt(value, 2)
 def rem = (4 - i.toString().size()%4)%4
 def nibble = Integer.toHexString(i)
 def pad = value.length() - (nibble.length()*4)
 if( pad < 0 ) {
  pad = 0
 }
 zeros << pad
 p21_rep << (rem + "0" * Math.ceil(pad/2) + nibble).toUpperCase()
}
//decode
p21_rep.eachWithIndex() { value, i ->
 d << value[0]
 def h = value.substring(1)
 hex << h
 def bs = Integer.toBinaryString(Integer.parseInt(h,16))
 out_bin << "0" * zeros[i] + bs
 def n = bs.length() + zeros[i]
 num_bits << n
 def bits = n + Integer.parseInt(value[0])
 padded << bits
 nibbles << bits / 4
}

printf("in:  %s\nout: %s\np21: %s\nextra bits: %s     hex: %s\n", in_bin, out_bin, p21_rep, d, hex)
printf("used bits:  %s extra+used bits: %s\nout_bin pad: %s  # nibbles: %s", num_bits, padded, zeros, nibbles)

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