#!/usr/bin/perl 

# A little utility to calculate room resonance modes.
# (c) 1998 Paul M. Winkler, zarmzarm_AT_erols.com
# Distributed under the terms of the GNU Public License.
# Blah blah blah blah.

# First we find our unit of measurement.

print '[F]eet, [i]nches, or [m]eters? ';
chomp ($units = <STDIN>);
if ($units =~ /^[Ii]/) {
    $speedosnd = 13536; 
}
elsif ($units =~ /^[Mm]/) {
    $speedosnd = 344; 
}
elsif ($units =~ /^[Ff]/) {
    $speedosnd = 1128; 
}
else {
    print "Huh? I'll assume you are using feet.\n";
    $speedosnd = 1128; 
}

# Now we get three dimensions.

print 'Length? ';
chomp ($l = <STDIN>);
 
print 'Width?  ';
chomp ($w = <STDIN>);

print 'Height? ';
chomp ($h = <STDIN>);

print "The total cubic volume is ", ($l * $w * $h ), "\n";

# Calculate and print the resonance modes ...

print "How many modes do you want to see? ";
chomp ($limit = <STDIN>); 
$printlimit = $limit;
for ($cnt = 0; $cnt < $limit; ++$cnt) {
    $l_modes[$cnt] = mode($cnt, $l);
    $w_modes[$cnt] = mode($cnt, $w);
    $h_modes[$cnt] = mode($cnt, $h);
    # write;
}

# Space the modes in a way that's easy to read.
# This is a bad strategy and needs to be totally redone.

for ($cnt = 0; $cnt < $limit; ++$cnt) {
    if ($l_modes[$cnt] < ($w_modes[$cnt] * 0.95 )) {
	shove_it (\@w_modes);
    }
    elsif ($l_modes[$cnt] > ($w_modes[$cnt] * 1.05)) {
	shove_it (\@l_modes);
    }
}

for ($cnt = 0; $cnt < $printlimit; ++$cnt) {
    write;
}

# print "\n\n Problem Zones:\n ==============\n";



# END


############# 
# A format for printing the modes.

format STDOUT_TOP =

Count  Length: @<<<  Width:  @<<<   Height: @<<<   
               $l,           $w,            $h
=====  ============  ============   ============
.

format STDOUT =
@<<<<  @<<<<<<<<<<<  @<<<<<<<<<<<   @<<<<<<<<<<<
$cnt, $l_modes[$cnt], $w_modes[$cnt], $h_modes[$cnt], 
.


#############
# A subroutine to calculate one room mode.
# This takes two arguments: the number of the mode (counting from
# zero), and a dimension in some arbitrary unit of measure.
# It returns a frequency in hz.
# $speedosnd is the speed of sound in units per second.

sub mode {
    return ($speedosnd * ($_[0] + 1) / ($_[1]));
}


sub shove_it {
    $aref = $_[0];
    @movers = splice(@$aref, $cnt);
    $$aref[$cnt] = 0;
    push(@$aref, @movers);
    ++$printlimit;
}