Re: Extracting full digits from a range

[davido]

The following code takes these steps:

1. Unpack two four-character strings while discarding a character in the middle. These strings will represent two hex sequences.
2. Pack the two hex strings.
3. Unpack the packed string as two network-endian unsigned shorts.
4. Generate a range from the low integral value to the high integral value.
5. Pack all of the integral elements of that range.
6. Unpack them as a series of hex strings.
7. Print them.

my $string = "293F:2945";

my ( $low, $high ) = unpack( 'nn', pack( 'H4H4', unpack( 'A4xA4', $str
+ing ) ) );
print "$_  " for unpack( '(H4)*', pack( 'n*', $low .. $high ) );

The output:

293f  2940  2941  2942  2943  2944  2945

Let's put it in a (debatably) well-named subroutine so we remember what this gem does:

sub enum_hex_range_from_string {
    my ( $low, $high ) 
        = unpack( 'nn', pack( 'H4H4', unpack( 'A4xA4', $string ) ) );
    return unpack( '(H4)*', pack( 'n*', $low .. $high ) );
}

Just add some camel casing randomly through the subroutine name and it would feel right at home in a PHP application.

The hardest part of coming up with something like this is keeping track of which of the many pack/unpack template tokens to use from [Hh] and [SsNnVv]. I have to admit to needing to experiment with a couple of one-liners to make sure my conversions were going the right direction.