#!/usr/bin/perl

# Generate a skew table

use Getopt::Std;

$skew= 4;		# defaults
$sectors= 64;

	getopts('hos:k:');

	if ($opt_h) {
		print "Usage:\n    skew -s N -k K\n";
		print "      N is sectors/track (default 64),\n";
		print "      K is skew factor (default 5)\n";
		print "      -o octal\n";
		exit(1);
	}
	$skew= $opt_k if defined $opt_k;
	$sectors= $opt_s if defined $opt_s;

	for ($i= 0; $i < $opt_s; ++$i) {			# mark table to make bad factors stand out
		$S[$i]= 99999;
	}

# Fill in the skew table. Note that many combinations of
# sector & skew do not repeat; we fix most of these by
# incrementing N if an iteration would overwrite a previous.

	$n= 0;
	for ($i= 0; $i < $sectors; ++$i) {
		$S[$n]= $i;
		$n += $skew;
		if ($n >= $sectors) {		# wraparound,
			$n -= $sectors;		# modulo SECTORS,
			++$n if $S[$n] || $n == 0;
		}
	}

# Display the table.

	print "Skew table, ${sectors}x$skew, ";
	print $opt_o ? "octal" : "decimal";

	$n= 0;
	for ($i= 0; $i < $sectors; ++$i) {
		if ($opt_o) {
			print sprintf ("\n%02o: ", $i) if $i % $skew == 0;
			print sprintf ("%2o ", $S[$i]);

		} else {
			print sprintf ("\n%02d: ", $i) if $i % $skew == 0;
			print sprintf ("%2d ", $S[$i]);
		}
	}
	print "\n";