Index: common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.412
diff -u -r1.412 common.inc
--- common.inc	15 Dec 2004 21:16:53 -0000	1.412
+++ common.inc	24 Dec 2004 00:27:23 -0000
@@ -606,6 +606,27 @@
 
   return TRUE;
 }
+
+/**
+ * Validate captcha input by a user.
+ *
+ * Ensures that the input matches the captcha variable contents to prevent
+ * automated scripts from submitting a form.
+ *
+ * @param $data
+ *   The input to check.
+ * @return
+ *   TRUE if the input data matches the captcha variable.
+ */
+function valid_captcha($data) {
+  $answer = variable_set('captcha_answer', '');
+
+  if ($answer == '') return FALSE;
+  if ($answer != $data) return FALSE;
+
+  return TRUE;
+}
+
 /**
  * @} End of "defgroup validation".
  */
@@ -1374,6 +1395,80 @@
   }
 
   return form_select($title, $name, $value, $weights, $description, $extra);
+}
+
+/**
+ * Format a captcha field.
+ *
+ * @return
+ *   A themed HTML string representing the field.
+ *
+ * A math question is generated along with the answer. The answer is saved to
+ * a variable which is referenced in the valid_captcha() function.
+ */
+function form_captcha() {
+
+  $numbers = array(
+    1 => t('one'),
+    2 => t('two'),
+    3 => t('three'),
+    4 => t('four'),
+    5 => t('five'),
+    6 => t('six'),
+    7 => t('seven'),
+    8 => t('eight'),
+    9 => t('nine'),
+    10 => t('ten'),
+    11 => t('eleven'),
+    12 => t('twelve')
+  );
+
+  $operators = array(
+    0 => array(name => t('plus'), symbol => '+'),
+    1 => array(name => t('minus'), symbol => '-'),
+    2 => array(name => t('multiplied by'), symbol => '*'),
+    3 => array(name => t('divided by'), symbol => '/')
+  );
+
+  $operator = rand(0,count($operators)-1);
+
+  // choose numbers based on operator to keep the math simple
+  switch($operator) {
+    case 0:
+      // do addition logic
+      $firstNumber = rand(1,count($numbers)-1);
+      $secondNumber = rand(1,count($numbers)-1);
+      $result = $firstNumber + $secondNumber;
+      break;
+    case 1:
+      // do subtraction logic
+      $firstNumber = rand(6,count($numbers)-1);
+      $secondNumber = rand(1,5);
+      $result = $firstNumber - $secondNumber;
+      break;
+    case 2:
+      // do multiplication logic
+      $firstNumber = rand(1,8);
+      $secondNumber = rand(1,8);
+      $result = $firstNumber * $secondNumber;
+      break;
+    case 3:
+      // do division logic
+      $secondNumber = rand(2,4);
+      $firstNumber = $secondNumber * rand(1,4);
+      $result = $firstNumber / $secondNumber;
+      break;
+  }
+
+  $question = t('What is ') . $numbers[$firstNumber].' ' .
+                $operators[$operator]['name'].' '.$numbers[$secondNumber] . '?';
+  $output = form_textfield($question, 'captcha', NULL, 15, 15,
+                t('This helps prevent automated submissions.'), NULL, TRUE);
+
+  // set captcha answer variable
+  variable_set('captcha_answer', $result);
+
+  return $output;
 }
 
 /**