base60.php

<?php
/* Code from http://tantek.pbworks.com/NewBase60
	License: http://creativecommons.org/licenses/by-sa/3.0/
	Author: Tantek Çelik <http://tantek.com>
*/

function strcat($a, $b) {
	return $a.$b;
}

function numtosxg($n) {
	$s = "";
	$m = "0123456789ABCDEFGHJKLMNPQRSTUVWXYZ_abcdefghijkmnopqrstuvwxyz";
	if ($n===undefined || $n===0) { return 0; }
	while ($n>0) {
		$d = $n % 60;
		$s = strcat($m[$d],$s);
		$n = ($n-$d)/60;
	}
	return $s;
}

function numtosxgf($n, $f) {
	$s = numtosxg($n);
	if ($f===undefined) { 
		$f=1; 
	}
	$f -= strlen($s);
	while ($f > 0) { 
		$s = strcat("0",$s); 
		--$f; 
	}
	return $s;
}

function sxgtonum($s) {
	$n = 0;
	$j = strlen($s);
	for ($i=0;$i<$j;$i++) { // iterate from first to last char of $s
		$c = ord($s[$i]); //  put current ASCII of char into $c  
		if ($c>=48 && $c<=57) { $c=$c-48; }
		else if ($c>=65 && $c<=72) { $c-=55; }
		else if ($c==73 || $c==108) { $c=1; } // typo capital I, lowercase l to 1
		else if ($c>=74 && $c<=78) { $c-=56; }
		else if ($c==79) { $c=0; } // error correct typo capital O to 0
		else if ($c>=80 && $c<=90) { $c-=57; }
		else if ($c==95) { $c=34; } // underscore
		else if ($c>=97 && $c<=107) { $c-=62; }
		else if ($c>=109 && $c<=122) { $c-=63; }
		else { $c = 0; } // treat all other noise as 0
		$n = 60*$n + $c;
	}
	return $n;
}

?>

shorten.php

<?php
/*
Plugin Name: Shorten
Plugin URI: http://singpolyma.net/plugins/shorten
Description: Provides a URL shortener in Wordpress.
Version: 0.1
Author: Stephen Paul Weber
Author URI: http://singpolyma.net
License: MIT license (http://www.opensource.org/licenses/mit-license.php)
*/

@include dirname(__FILE__).'/base60.php';

			  if(!$_SERVER['SCRIPT_URI'] && $_SERVER['REQUEST_URI'])
			    $_SERVER['SCRIPT_URI'] = $_SERVER['REQUEST_URI'];
			  if(!$_SERVER['SCRIPT_URI'] && $_SERVER['SCRIPT_NAME'])
			    $_SERVER['SCRIPT_URI'] = $_SERVER['SCRIPT_NAME'];

			  $path = preg_replace('#^'.preg_replace('/https?/','https?',get_bloginfo('home')).'#','',$_SERVER['SCRIPT_URI']);
			  preg_match('/^\/?\/p\/(\d+)\/?$/', $path, $matches);

			  if($matches[1]) {
			    header('Location: '.get_bloginfo('home').'?shortened&p='.$matches[1], true, 301);
			    exit;
			  } else if(function_exists('sxgtonum')) {
			    preg_match('/^\/?\/s\/([0-9a-zA-Z]+)\/?$/', $path, $matches);
			    if($matches[1]) {
			      header('Location: '.get_bloginfo('home').'?shortened&p='.sxgtonum($matches[1]), true, 301);
			      exit;
			    }
			  }

function shortened_head() {
  global $post;
  $shorten_options = get_option('shorten_options');
  $shorten_base = $shorten_options['shorten_base'];
  if(is_page() || is_single()) {
    if(function_exists('numtosxg')) {
      echo '<link rev="canonical" rel="self alternate shorter short_url" href="'.$shorten_base.'/s/'.numtosxg($post->ID).'" />';
      echo '<link rel="self alternate shorter short_url" href="'.$shorten_base.'/p/'.$post->ID.'" />';
    } else {
      echo '<link rev="canonical" rel="self alternate shorter short_url" href="'.$shorten_base.'/p/'.$post->ID.'" />';
    }
  }
}

add_action('wp_head', 'shortened_head');


// Manage plugin options
//
add_action( 'admin_init', 'shorten_register_settings' );
function shorten_register_settings() {
  register_setting( 'shorten_options', 'shorten_options' );
}

// Plugin Options Menu
function shorten_plugin_menu() {
  add_options_page('Shorten Options', 'Shorten', 'manage_options', 'shorten-options', 'shorten_plugin_options_page');
}

function shorten_plugin_options_page() {
   ?>
   <div class="wrap">
       <h2>Shorten Options</h2>
       <form method="post" action="options.php">
    <?php settings_fields('shorten_options'); ?>
    <?php $shorten_options = get_option('shorten_options'); ?>
           <table class="form-table">
               <tr valign="top"><th scope="row">Shortlink Domain</th>
                   <td><input type="text" name="shorten_options[shorten_base]" value="<?php echo $shorten_options['shorten_base']; ?>" /></td>
               </tr>
           </table>
           <p class="submit">
           <input type="submit" class="button-primary" value="<?php _e('Save Changes') ?>" />
           </p>
       </form>
   </div>
   <?php   
    }

add_action('admin_menu', 'shorten_plugin_menu');

?>

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