Why is my unpacking printing wrong values?

Question

Why am I getting the wrong answers / values?

The correct values ​​that it should print are 1, 2175, 4 , but instead, I always get 1, 3, 0 ?!

 my $data = pack ('C*', map hex, split /\s+/, "01 00 00 00 7F 08 03 00 21 04 80 04 FF D7 FB 0C EC 01 44 00 61 1D 00 00 10 3B 00 00 FF D7 FB 0C 00 00 8C 64 00 00 EC 45"); ($obj->{Version}, $obj->{res1}, $obj->{EARFCN}, $tmp1, $obj->{res2}, $tmp2)=unpack("C C3 v CCV", $data); $obj->{band} = ($tmp1 & 0xfc) >> 2; print "\n".$obj->{Version}; # Should print 1 print "\n".$obj->{EARFCN}; # Should print 2175 print "\n".$obj->{band}; # Should print 4. Note: this is the first 6 bits from MSB of $tmp1. print "\n"; 

Answer 1

Debug output:

  DB<1> $data = pack ('C*', map hex, split /\s+/, "01 00 00 00 7F 08 03 00 21 04 80 04 FF D7 FB 0C EC 01 44 00 61 1D 00 00 10 3B 00 00 FF D7 FB 0C 00 00 8C 64 00 00 EC 45") DB<2> x unpack("C C3 v CCV", $data) 0 1 1 0 2 0 3 0 4 2175 5 3 6 0 7 75498529 

The C3 pattern outputs three unsigned bytes, not a string of length three.

I think you want a3 instead. See Perldoc pack ()

Answer 2

I made two mistakes.

I should have used the a3 specifier instead of C3 . So he must say:

unpack("C a3 v CCV", $data);

and

$obj->{band} = ($tmp1 & 0xfc) >> 2; really equal to 0. not 4.

Answer 3

There is no template for 24-bit words. (This type of machine does not.) You can use any of the following snippets.

You want band be the most significant 6 bits of a 16-bit word ( y in yyyy yyxx xxxx xxxx ). To do this, use $_ >> 10 .

 ( $obj->{Version}, my $tmp0, $obj->{EARFCN}, my $tmp1, $obj->{res2}, my $tmp2 ) = unpack("C a3 v CCV", $data); $obj->{res1} = unpack("V", $tmp0."\x00"); $obj->{band} = $tmp1 >> 10; 

or

 ( my $tmp0, $obj->{EARFCN}, my $tmp1, $obj->{res2}, my $tmp2 ) = unpack("V v CCV", $data); $obj->{Version} = $tmp0 & 0xFF; $obj->{res1} = $tmp0 >> 8; $obj->{band} = $tmp1 >> 10;