#!/usr/bin/env perl
#use v5.20;
#use feature qw(signatures);
#no warnings qw(experimental::signatures);

use v5.36;
use autodie;

exit 1 if not @ARGV;

sub read_file ($fh, $chunk_size=65536) {
    # Return the next chunk, including to the end of line.
    read($fh, my $chunk, $chunk_size);
    if (length($chunk) && substr($chunk, -1) ne "\n") {
        return $chunk if eof($fh);
        $chunk .= readline($fh);
    }
    return $chunk;
}

my $mul_pattern = 'mul\(\d{1,3},\d{1,3}\)';
my $filename = shift;
my $count = 0;

if (open(my $fh, '<', $filename)) {
    while (length(my $chunk = read_file($fh))) {
        $count += () = $chunk =~ m/$mul_pattern/g;
    }
}

print "Found $count matches.\n";