# Copyright (C) 1996 - 2001 Tim Witham <twitham@pcocd2.intel.com>
# Copyright (C) 2015 Brent Baccala <cosine@freesoft.org>

# (see the files README and COPYING for more details)

# xoscope external math filter command example in perl

# !!! Please see bottom of this file for instructions and examples !!!

$| = 1;				# unbuffer stdout
$0 =~ s!.*/!!;			# reduce to program basename
$func = $ENV{FUNC};		# get function to run from environment
$samples = $ARGV[1] || 640;	# assume 640 total samples per screen
$func =~ s/\#.*$//;		# toss comments
$func =~ s/^\s*(\$0\s*=)?\s*//;	# and assumed leading/trailing stuff, if any
$func =~ s/\s*;*\s*$//;
die "usage: $0 'perl math function of \$t, \$ch1 and \$ch2' [sample length]\n"
    unless $func;		# oops
$func = "\$out = $func;";	# '$out=' and ';' are implied around function

open(IN, '<&3')			# open non-standard input for reading
    || die "$0: Can't read input: $!\n";
open(OUT, '>-')			# and stdout for writing
    || die "$0: Can't write stdout: $!\n";

$pi = 3.14159265359;		# define pi for user's convenience
$t = 0;				# sample position number (time)
for (1..$samples) {		# initialize sample memory "shift registers"
    push(@ch1, 0);		# channel 1 (left)
    push(@ch2, 0);		# channel 2 (right)
    push(@out, 0);		# output back to software channel
}

# For efficiency, we now dynamically build a while loop around the
# user's function then evaluate (compile and run) it once.

# begin of loop: how to read the samples (two shorts) from stdin:
$begin = '
while(1) {
    sysread(IN, $buff, 2) || exit;
    $ch1 = unpack(\'s\', $buff);
    sysread(IN, $buff, 2) || exit;
    $ch2 = unpack(\'s\', $buff);

';

# end: how to increment time, remember the samples, and write result to stdout:
$end = '

    $t = 0 if ++$t >= $samples;';

# sample history is expensive, so we only remember those the function needs:
$end .= '
    pop(@ch1); unshift(@ch1, $ch1);' if $func =~ /\$ch1\[/;
$end .= '
    pop(@ch2); unshift(@ch2, $ch2);' if $func =~ /\$ch2\[/;
$end .= '
    pop(@out); unshift(@out, $out);' if $func =~ /\$out\[/;

$end .= '
    syswrite(OUT, pack(\'s\', $out), 2) || exit;
}
';

# now put the loop around the user's function
eval $begin.$func.$end;		# and finally run the loop forever
warn "$@\n" if $@;		# show any user syntax errors on stderr

__END__
{}