/* compress.pc - lrb - 3/22/2010 (pseudocode)

compress [
 open output file
 put "signature" byte FF in output array
 open input file
 read it into an array
 set nibble to 1
 get byte from array
 while (bytes remain) [
  determine byte's "class," i.e. "rare" or "common"
  if nibble = 1 [
   if rare rtn1
   else rtn2
   ]
  else [
   if rare rtn3
   else rtn4
   ]
  get byte from array
  ]
 if nibble = 2 [ /* note change!
  put HF in output array
  put CC in output array /* note change!
  ]
 else [
  put FC in output array
  ]
 write output file from output array
 ]

rtn1 [
 put FH in output array where H is hex value of index of character in rare
 ]

rtn2 [
 save in H the hex value of index of character in common
 set nibble to 2
 ]

rtn3 [
 put HF in output array 
 save in H the hex value of index of character in rare /* note change!
 ]

rtn4 [
 put HK in output array where K is hex value of index of character in common /* note change!
 set nibble to 1
 ]