my $FIONREAD = do {
    use Config qw(config_re);
    my ($archname) = config_re('archname');

    if ($archname =~ /(?:irix|mips)/i) {
        # IRIX; Linux on MIPS
        0x467f;
    }
    elsif ($archname =~ /(?:alpha|powerpc|ppc|sparc)/i) {
        # OSF/1, Tru64; Linux on Alpha, PowerPC, SPARC
        0x4004667f;
    }
    elsif ($^O =~ /(?:hp-?ux|linux)/i) {
        # HP-UX; Linux on AArch64, ARM, PA-RISC, RISC-V, s390x, x86_64
        0x541b;
    }
    elsif ($^O =~ /(?:aix|bsd|darwin|dragonfly|mswin|mingw|msys|cygwin|solaris)/i) {
        # AIX, BSD derivatives, macOS, Windows/Cygwin, Solaris
        0x4004667f;
    }
    elsif ($^O =~ /haiku/i) {
        # Haiku (BeOS-like OS)
        0xbe000001;
    }
    else {
        ##
        # MCE::Semaphore::count() unimplemented in this platform.
        # Pull request or email the author $^O, archname, and FIONREAD.
        #
        # $ perl -MConfig -le 'print $^O, ": ", $Config{archname}'
        # $ python3 -c 'import termios; print(hex(termios.FIONREAD))'
        #
        # $ cat fionread.c
        #
        #   #include <stdio.h>
        #   #include <sys/ioctl.h>
        #   int main() {
        #       printf("%#08lx\n", FIONREAD);
        #       return 0;
        #   }
        #
        # $ cc -o fionread fionread.c
        # $ ./fionread
        ##

        0x0;
    }
};

# $sem->count

sub count {
    die 'MCE::Semaphore::count() unimplemented in this platform'
        unless $FIONREAD;

    my $count = pack('L', 0);
    ioctl($_[0]->{r_sock}, $FIONREAD, $count);
    unpack('L', $count);
}