Please find the (simplified) program below. The file is simulated with an array. It is running itself.

#!/usr/bin/perl 
use strict;
use warnings;
$\="\n"; $,=", ";

#------------------------------------------------
my($f, $fpos, $fposlen, @data, $byte1, @byte2, $crc, @crcval); 
initCRC();
ReadDatFile();
exit;

#------------------------------------------------
sub ReadDatFile
{ # simulate file read:
  # three datasets:  0,1,2,3,4,5,6,7,8,9  and  10,11,2,3,4,5,6,7,8,9 a
+nd 20,11,2,3,4,5,6,7,18,19
  my @file=(0x00, 0xc0,0xff,0x80,1,2,3,4,5,6,7,8,9,0x8e,   10,0x80,0x8
+0,11,0x9d,   20,0xc0,0x01,0x80,18,19,0x1c,   0xff);
  $f.=chr($_)|'' foreach (@file);
  
  $crc=255; $fposlen=length($f); $fpos=0;
  @byte2=(0,0,0,0,0,0,0,0);
  readByte(); $data[0]=$_;                              # first data
  
  do
  { readByte(); $byte1=$_;                              # BYTE1: $_
    if ($byte1 & 0x80) {readByte(); $byte2[0]=$_; } 
    if ($byte1 & 0x40) {readByte(); $byte2[1]=$_; }
    if ($byte1 & 0x20) {readByte(); $byte2[2]=$_; }
    if ($byte1 & 0x10) {readByte(); $byte2[3]=$_; } 
    if ($byte1 & 0x08) {readByte(); $byte2[4]=$_; }
    if ($byte1 & 0x04) {readByte(); $byte2[5]=$_; }
    if ($byte1 & 0x02) {readByte(); $byte2[6]=$_; }
    if ($byte1 & 0x01) {readByte(); $byte2[7]=$_; }

    do_byte2( 0) if ($byte1 & 0x80); 
    do_byte2( 8) if ($byte1 & 0x40); 
    do_byte2(16) if ($byte1 & 0x20);
    do_byte2(24) if ($byte1 & 0x10); 
    do_byte2(32) if ($byte1 & 0x08); 
    do_byte2(40) if ($byte1 & 0x04); 
    do_byte2(48) if ($byte1 & 0x02); 
    do_byte2(56) if ($byte1 & 0x01); 
    
    readByte(); if ($crc>0) {print "ERROR: CRC (POS:$fpos)"; exit; }  
+ # crc check
    $crc=255;     

    print @data;           # ---- USE DATA ---------
    
    readByte(); $data[0]=$_;                         # next dataset
  } while ($_<255);
  
}

sub do_byte2
{ my $bpos=$_[0];                                     # pos in data fr
+om byte0
  my $pp=$byte2[$bpos>>3];
  if ($pp & 0x80) {readByte(); $data[$bpos+1]=$_;}    # take value int
+o data array
  if ($pp & 0x40) {readByte(); $data[$bpos+2]=$_;}
  if ($pp & 0x20) {readByte(); $data[$bpos+3]=$_;}
  if ($pp & 0x10) {readByte(); $data[$bpos+4]=$_;}
  if ($pp & 0x08) {readByte(); $data[$bpos+5]=$_;}
  if ($pp & 0x04) {readByte(); $data[$bpos+6]=$_;}
  if ($pp & 0x02) {readByte(); $data[$bpos+7]=$_;}
  if ($pp & 0x01) {readByte(); $data[$bpos+8]=$_;}
}

sub readByte
{ if ($fposlen==$fpos) {print "Last data structure not complete !"; ex
+it;}
  $_=vec($f,$fpos,8); 
  $crc=$crcval[$crc^$_];         # CRC     
  $fpos++;  
}

sub initCRC
{ for my $v (0..255)
  { $_=$v;
    for my $r (1..8)
    { if (($_&1)>0) {$_=($_>>1)^0x8c;}
      else          {$_=$_>>1;}  
    }
    $crcval[$v]=$_;  
} }
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