In 1993, I wrote some code to parse a C header file with a bunch of numerical token values in #define statements. Then print them out in this series manner, in order to find holes and duplicates. Amazingly, I was able to dig that code up and adapt it for this problem.

Ignore my overuse of printf and the unused flag to turn on hex vs decimal printing. This reflects some of my earliest perl coding, and it's pretty obvious that I'm a C programmer by trade.

#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;
use List::Util qw(min);

my $opt_x = 0;  # Original code allows hex or decimal

my @list = (1, 2, 3, 6, 9, 10, 13, 22, 20, 19, 15, 21);

my %Count;
$Count{$_}++ foreach @list;

my $number;

foreach $number (sort numerically keys(%Count))
{
    my $count = $Count{$number};

    if ($count > 1)
    {
        printf "Token value %d occurs %d times.\n",
                $number, $count if (!$opt_x);
        printf "Token value 0x%x occurs %d times.\n",
                $number, $count if ( $opt_x);
    }
}

# Print a list of the form:
# 100,102,104,108-110,112-115,119

my $expected = min(@list);
my $in_list=0;
my $list_start=0;
my $comma="";

foreach $number (sort numerically keys(%Count))
{
    if (($number == $expected) && ($in_list))
    {
        # Accumulate list
        $in_list++;
    }
    elsif (($number == $expected) && ($in_list == 0))
    {
        $list_start=$number;
        $in_list = 1;
    }
    elsif ($in_list > 1)        # not expected
    {
        printf "%s%d-%d",
                $comma, $list_start, $expected-1
                if (!$opt_x);
        printf "%s0x%x-0x%x",
                $comma, $list_start, $expected-1
                if ( $opt_x);
        $comma = ",";
        $list_start = $number;
        $in_list = 1;
    }
    else        # in_list == 1 and not expected
    {
        printf "%s%d",   $comma, $list_start if (!$opt_x);
        printf "%s0x%x", $comma, $list_start if ( $opt_x);
        $comma = ",";
        $list_start = $number;
        $in_list = 1;
    }

    $expected = $number + 1;
}

if ($in_list > 1)       # Terminate
{
    printf "%s%d-%d",
            $comma, $list_start, $expected-1
            if (!$opt_x);
    printf "%s0x%x-0x%x",
            $comma, $list_start, $expected-1
            if ( $opt_x);
}
elsif ($in_list)
{
    printf "%s%d",   $comma, $list_start if (!$opt_x);
    printf "%s0x%x", $comma, $list_start if ( $opt_x);
}
else
{
    printf "%s%d",   $comma, $number if (!$opt_x);
    printf "%s0x%x", $comma, $number if ( $opt_x);
}
print "\n";


sub numerically { return $a <=> $b; }

exit 0;
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