function _locale_import_parse_arithmetic

Parses and sanitizes an arithmetic formula into a PHP expression

While parsing, we ensure, that the operators have the right precedence and associativity.

Parameters

$string: A string containing the arithmetic formula.

Return value

The PHP version of the formula.

Related topics

File

drupal/includes/locale.inc, line 1286

Administration functions for locale.module.

Code

function _locale_import_parse_arithmetic($string) {

  // Operator precedence table
  $precedence = array(
    "(" => -1,
    ")" => -1,
    "?" => 1,
    ":" => 1,
    "||" => 3,
    "&&" => 4,
    "==" => 5,
    "!=" => 5,
    "<" => 6,
    ">" => 6,
    "<=" => 6,
    ">=" => 6,
    "+" => 7,
    "-" => 7,
    "*" => 8,
    "/" => 8,
    "%" => 8,
  );

  // Right associativity
  $right_associativity = array(
    "?" => 1,
    ":" => 1,
  );
  $tokens = _locale_import_tokenize_formula($string);

  // Parse by converting into infix notation then back into postfix
  // Operator stack - holds math operators and symbols
  $operator_stack = array();

  // Element Stack - holds data to be operated on
  $element_stack = array();
  foreach ($tokens as $token) {
    $current_token = $token;

    // Numbers and the $n variable are simply pushed into $element_stack
    if (is_numeric($token)) {
      $element_stack[] = $current_token;
    }
    elseif ($current_token == "n") {
      $element_stack[] = '$n';
    }
    elseif ($current_token == "(") {
      $operator_stack[] = $current_token;
    }
    elseif ($current_token == ")") {
      $topop = array_pop($operator_stack);
      while (isset($topop) && $topop != "(") {
        $element_stack[] = $topop;
        $topop = array_pop($operator_stack);
      }
    }
    elseif (!empty($precedence[$current_token])) {

      // If it's an operator, then pop from $operator_stack into $element_stack until the
      // precedence in $operator_stack is less than current, then push into $operator_stack
      $topop = array_pop($operator_stack);
      while (isset($topop) && $precedence[$topop] >= $precedence[$current_token] && !($precedence[$topop] == $precedence[$current_token] && !empty($right_associativity[$topop]) && !empty($right_associativity[$current_token]))) {
        $element_stack[] = $topop;
        $topop = array_pop($operator_stack);
      }
      if ($topop) {
        $operator_stack[] = $topop;

        // Return element to top
      }
      $operator_stack[] = $current_token;

      // Parentheses are not needed
    }
    else {
      return FALSE;
    }
  }

  // Flush operator stack
  $topop = array_pop($operator_stack);
  while ($topop != NULL) {
    $element_stack[] = $topop;
    $topop = array_pop($operator_stack);
  }

  // Now extract formula from stack
  $previous_size = count($element_stack) + 1;
  while (count($element_stack) < $previous_size) {
    $previous_size = count($element_stack);
    for ($i = 2; $i < count($element_stack); $i++) {
      $op = $element_stack[$i];
      if (!empty($precedence[$op])) {
        $f = "";
        if ($op == ":") {
          $f = $element_stack[$i - 2] . "):" . $element_stack[$i - 1] . ")";
        }
        elseif ($op == "?") {
          $f = "(" . $element_stack[$i - 2] . "?(" . $element_stack[$i - 1];
        }
        else {
          $f = "(" . $element_stack[$i - 2] . $op . $element_stack[$i - 1] . ")";
        }
        array_splice($element_stack, $i - 2, 3, $f);
        break;
      }
    }
  }

  // If only one element is left, the number of operators is appropriate
  if (count($element_stack) == 1) {
    return $element_stack[0];
  }
  else {
    return FALSE;
  }
}