Hello Perlmonks,

From an encrypted string I need to decode a 2-byte part, 16 bit. The 16 bit represent a date (year, month, day). The decoding is done using Crypt::DES. The 2-byte part is extracted with $packed_d = substr($packed_d,0,2); I then need the first 7 bits converted into a year, 4 bits for the month, and 5 bits for the day.

My code for selection of the bits does not work. The bitwise-& with my hex and packed_d always returns 0x00. In the example I construct a packed_d that I found in the data. Can someone tell me why "$packed_d & 0xFE00" always returns 0x00 ? (I replaced 0xFE00 with 0xFFFF and it still returns 0x00)

Thank you. 

# raw contains the decrypted data
my ($p1,$p1,$p3,$packed_d)=split(/\000/,$raw,4);
$packed_d = substr($packed_d,0,2); #cut padding

# temporary construction of packed_d
my( $packed_d ) = pack( 'H4', d262 );

my $y = (($packed_d & 0xFE00) >> 9) + 4;
my $m = (($packed_d & 0x01E0) >> 5) - 1;
my $d = ($packed_d & 0x001F);

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In reply to selecting and converting a bitstring by momo33

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