Question

I have some 256-character strings of hexadecimal characters which represent a sequence of bit flags, and I’m trying to convert them back into a bitstring so I can manipulate them with &, |, vec and the like. The hex strings are written in integer-wide big-endian groups, such that a group of 8 bytes like "76543210" should translate to the bitstring "\x10\x32\x54\x76", i.e. the lowest 8 bits are 00001000.

The problem is that pack‘s “h” format works on one byte of input at a time, rather than 8, so the results from just using it directly won’t be in the right order. At the moment I’m doing this:

my $bits = pack("h*", join("", map { scalar reverse $_ } unpack("(A8)*", $hex)));

which works, but feels hackish. It seems like there ought to be a cleaner way, but my pack-fu is not very strong. Is there a better way to do this translation?

Answer 1

my $hex = "7654321076543210";  # can be as long as needed
my $bits = pack("V*", unpack("N*", pack("H*", $hex)));
print unpack("H*", $bits);  #: 1032547610325476