1 evalmath.inc EvalMath::nfx($expr)

File

core/includes/evalmath.inc, line 169

Class

EvalMath

Code

function nfx($expr) {

  $index = 0;
  $stack = new EvalMathStack;
  $output = array(); // postfix form of expression, to be passed to pfx()
  $expr = trim(strtolower($expr));

  $ops = array('+', '-', '*', '/', '^', '_');
  $ops_r = array('+' => 0, '-' => 0, '*' => 0, '/' => 0, '^' => 1); // right-associative operator?
  $ops_p = array('+' => 0, '-' => 0, '*' => 1, '/' => 1, '_' => 1, '^' => 2); // operator precedence

  $expecting_op = false; // we use this in syntax-checking the expression
  // and determining when a - is a negation

  if (preg_match("/[^\w\s+*^\/()\.,-]/", $expr, $matches)) { // make sure the characters are all good
    return $this->trigger("illegal character '{$matches[0]}'");
  }

  while (1) { // 1 Infinite Loop ;)
    $op = substr($expr, $index, 1); // get the first character at the current index
    // find out if we're currently at the beginning of a number/variable/function/parenthesis/operand
    $ex = preg_match('/^([a-z]\w*\(?|\d+(?:\.\d*)?|\.\d+|\()/', substr($expr, $index), $match);
    //===============
    if ($op == '-' and !$expecting_op) { // is it a negation instead of a minus?
      $stack->push('_'); // put a negation on the stack
      $index++;
    }
    elseif ($op == '_') { // we have to explicitly deny this, because it's legal on the stack
      return $this->trigger("illegal character '_'"); // but not in the input expression
      //===============
    }
    elseif ((in_array($op, $ops) or $ex) and $expecting_op) { // are we putting an operator on the stack?
      if ($ex) { // are we expecting an operator but have a number/variable/function/opening parethesis?
        $op = '*';
        $index--; // it's an implicit multiplication
      }
      // heart of the algorithm:
      while ($stack->count > 0 and ($o2 = $stack->last()) and in_array($o2, $ops) and ($ops_r[$op] ? $ops_p[$op] < $ops_p[$o2] : $ops_p[$op] <= $ops_p[$o2])) {
        $output[] = $stack->pop(); // pop stuff off the stack into the output
      }
      // many thanks: http://en.wikipedia.org/wiki/Reverse_Polish_notation#The_algorithm_in_detail
      $stack->push($op); // finally put OUR operator onto the stack
      $index++;
      $expecting_op = false;
      //===============
    }
    elseif ($op == ')' and $expecting_op) { // ready to close a parenthesis?
      while (($o2 = $stack->pop()) != '(') { // pop off the stack back to the last (
        if (is_null($o2)) {
          return $this->trigger("unexpected ')'");
        }
        else {
          $output[] = $o2;
        }
      }
      if (preg_match("/^([a-z]\w*)\($/", $stack->last(2), $matches)) { // did we just close a function?
        $fnn = $matches[1]; // get the function name
        $arg_count = $stack->pop(); // see how many arguments there were (cleverly stored on the stack, thank you)
        $output[] = $stack->pop(); // pop the function and push onto the output
        if (in_array($fnn, $this->fb)) { // check the argument count
          if ($arg_count > 1) {
            return $this->trigger("too many arguments ($arg_count given, 1 expected)");
          }
        }
        elseif (array_key_exists($fnn, $this->f)) {
          if ($arg_count != count($this->f[$fnn]['args'])) {
            return $this->trigger("wrong number of arguments ($arg_count given, " . count($this->f[$fnn]['args']) . " expected)");
          }
        }
        else { // did we somehow push a non-function on the stack? this should never happen
          return $this->trigger("internal error");
        }
      }
      $index++;
      //===============
    }
    elseif ($op == ',' and $expecting_op) { // did we just finish a function argument?
      while (($o2 = $stack->pop()) != '(') {
        if (is_null($o2)) {
          return $this->trigger("unexpected ','"); // oops, never had a (
        }
        else {
          $output[] = $o2; // pop the argument expression stuff and push onto the output
        }
      }
      // make sure there was a function
      if (!preg_match("/^([a-z]\w*)\($/", $stack->last(2), $matches)) {
        return $this->trigger("unexpected ','");
      }
      $stack->push($stack->pop() + 1); // increment the argument count
      $stack->push('('); // put the ( back on, we'll need to pop back to it again
      $index++;
      $expecting_op = false;
      //===============
    }
    elseif ($op == '(' and !$expecting_op) {
      $stack->push('('); // that was easy
      $index++;
      //===============
    }
    elseif ($ex and !$expecting_op) { // do we now have a function/variable/number?
      $expecting_op = true;
      $val = $match[1];
      if (preg_match("/^([a-z]\w*)\($/", $val, $matches)) { // may be func, or variable w/ implicit multiplication against parentheses...
        if (in_array($matches[1], $this->fb) or array_key_exists($matches[1], $this->f)) { // it's a func
          $stack->push($val);
          $stack->push(1);
          $stack->push('(');
          $expecting_op = false;
        }
        else { // it's a var w/ implicit multiplication
          $val = $matches[1];
          $output[] = $val;
        }
      }
      else { // it's a plain old var or num
        $output[] = $val;
      }
      $index += strlen($val);
      //===============
    }
    elseif ($op == ')') { // miscellaneous error checking
      return $this->trigger("unexpected ')'");
    }
    elseif (in_array($op, $ops) and !$expecting_op) {
      return $this->trigger("unexpected operator '$op'");
    }
    else { // I don't even want to know what you did to get here
      return $this->trigger("an unexpected error occured");
    }
    if ($index == strlen($expr)) {
      if (in_array($op, $ops)) { // did we end with an operator? bad.
        return $this->trigger("operator '$op' lacks operand");
      }
      else {
        break;
      }
    }
    while (substr($expr, $index, 1) == ' ') { // step the index past whitespace (pretty much turns whitespace
      $index++; // into implicit multiplication if no operator is there)
    }

  }
  while (!is_null($op = $stack->pop())) { // pop everything off the stack and push onto output
    if ($op == '(') {
      return $this->trigger("expecting ')'"); // if there are (s on the stack, ()s were unbalanced
    }
    $output[] = $op;
  }
  return $output;
}