Probably slower, but leveraging RE's and getting rid of the copy to $padded makes it more compact. 
sub prepchksum {
    my ($payload) = @_;
    printf "BEFORE = %s\n", (CORE::unpack "H*", $payload);
    if (length($payload)%2) {
      $payload =~ s#(.)$#\0$1#;
      printf "MID1   = %s\n", (CORE::unpack "H*", $payload);
      # Compensate off-by-one error
      if (ord(substr $payload, -1) >= 128) {
         $payload=~s#(.)(.)$#pack('CC',(ord($1)-1)&255,
             (ord($2)-1)&255)#e;
      }
   }
   printf "AFTER  = %s\n", (CORE::unpack "H*", $payload);
}

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In reply to Re: Compensate for bad inet checksum routine by kschwab
in thread Compensate for bad inet checksum routine by VinsWorldcom

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