有个网友写信给我谈到关于PHP计算工资问题。我以前一篇文章中谈到过一种计算工资的方法，不过是偷巧，利用现有的表达式的工具，现在既然有人想要，我就给出一个逆波兰的算法。
我们的目标是实现如下的计算公式：
假设有一个计算公式如下： $expression = "(F1*F12+10.34)";
其中的变量值如下：
$expression_value = Array('F1'=>10,
'F12'=>20);
我们希望用PHP构建一个类来计算出这个表达式的值。这种应用主要用于web工资管理中，用户可以自定义其工资相公式的情况
$rpn = new Math_Rpn();
$rpn->setExpressionValue($expression_value);
echo $rpn->calculate($expression,'deg',false); // 即为相应的值
解析逆波兰表达式的方法，编译原理中有，就是先把表达式分解成符号数组，然后求逆波兰式，最后根据逆波兰式得到其结果。
我分别把三个函数贴在下面，其实本质我就是对Pear的RPN函数进行了Hack.
function _stringToArray () {
$temp_operator = null;
$temp_value = null;
$this->_input = str_replace(" ","",$this->_input);
for($i = 0; $i < strlen($this->_input); $i++) {
if ($this->_input[$i] == ' ') {
if ($temp_operator != null) {
array_push($this->_input_array, $temp_operator);
$temp_operator = null;
}
if ($temp_value != null) {
array_push($this->_input_array, $temp_value);
$temp_value = null;
}
} elseif (($temp_value == null) && $temp_operator != ')' && (!array_key_exists($temp_operator,$this->_operation) || !array_key_exists(2,$this->_operation[$temp_operator]) || $this->_operation[$temp_operator][2]>0) && ($this->_input[$i] == '-')) {
if ($temp_operator != null) {
array_push($this->_input_array, $temp_operator);
$temp_operator = null;
}
array_push($this->_input_array, '-1');
array_push($this->_input_array, '*');
//} elseif ((is_numeric($this->_input[$i])) || ($this->_input[$i] == '.')) {
} elseif ((is_numeric($this->_input[$i])) || ($this->_input[$i] == '.') || ($this->_input[$i] == 'F')) {
if ($temp_operator != null) {
array_push($this->_input_array, $temp_operator);
$temp_operator = null;
}
$temp_value .= $this->_input[$i];
} else {
if ($this->_keyExists($temp_operator, $this->_operation, 1)) {
array_push($this->_input_array, $temp_operator);
$temp_operator = null;
}
if ($temp_value != null) {
array_push($this->_input_array, $temp_value);
$temp_value = null;
}
$temp_operator .= $this->_input[$i];
}
}
if ($temp_operator != null && $temp_operator != ' ') {
array_push($this->_input_array, $temp_operator);
} elseif($temp_value != null && $temp_value != ' ') {
array_push($this->_input_array, $temp_value);
}
// $this->_testInput();
print_r($this->_expression_value);
print_r($this->_input_array);
return $this->_input_array;
}
function _arrayToRpn() {
if ($this->_error <> null) {
$this->_output = array();
return $this->_output;
}
for($i = 0; $i < count($this->_input_array); $i++) {
$temp = $this->_input_array[$i];
if (is_numeric($temp)) {
$this->_outputAdd($temp);
} else if($this->_keyExists($temp, $this->_expression_value, 0)) {
$this->_outputAdd($this->_expression_value[$temp]);
} else {
if ($temp == ')') {
while(!$this->_stackEmpty() && ($this->_stackPriority() >= 1)) {
$this->_outputAdd($this->_stackDelete());
}
if (!$this->_stackEmpty()) {
$this->_stackDelete();
}
} elseif ($temp=='(') {
$this->_stackAdd($temp);
} elseif (($this->_stackEmpty()) || (($this->_priority($temp) > $this->_stackPriority()))) {
$this-> _stackAdd($temp);
} else {
while(!$this->_stackEmpty() && ($this->_priority($temp) <= $this->_stackPriority())) {
$this->_outputAdd($this->_stackDelete());
}
$this->_stackAdd($temp);
}
}
}
while(!$this->_stackEmpty()) {
$this->_outputAdd($this->_stackDelete());
}
return $this->_output;
}
function _rpnToValue() {
$time1 = $this->_getMicroTime();
if ($this->_error <> null) {
$this->_value = null;
return $this->_value;
}
$this->_value = 0;
$temp = $this->_output;
do {
$pos = $this->_nextOperator($temp);
if ($pos == -1) {
$this->_error = $this->_raiseError('Syntax error');
$this->_value = null;
return $this->_value;
}
$operator = $this->_operation[$temp[$pos]];
$arg = $operator[2];
$function = $operator[3];
if (($arg==2) && (!isset($temp[$pos-1]) || !is_numeric($temp[$pos-1]) || !isset($temp[$pos-2]) || !is_numeric($temp[$pos-2]))) {
$this->_error = $this->_raiseError('Syntax error');
$this->_value = null;
return $this->_value;
} elseif (($arg==1) && (!isset($temp[$pos-1]) || !is_numeric($temp[$pos-1]))) {
$this->_error = $this->_raiseError('Syntax error');
$this->_value = null;
return $this->_value;
}
if(is_array($function)) {
if($arg==2) $arg_array = array($temp[$pos-2],$temp[$pos-1]);
elseif($arg==1) $arg_array = array($temp[$pos-1]);
else $arg_array = array();
if($function['type'] == 'userFunction') {
$this->_value = call_user_func_array($function['function'], $arg_array);
} else {
$function_array = array(&$function['class'], $function['method']);
$this->_value = call_user_func_array($function_array, $arg_array);
}
} else {
$this->_value = $this->$function($temp, $pos);
}
if ($this->_isNan($this->_value)) {
$this->_error = $this->_raiseError('NAN value');
$this->_value = null;
return $this->_value;
} elseif ($this->_isInfinite($this->_value)) {
$this->_error = $this->_raiseError('Infinite value');
$this->_value = null;
return $this->_value;
} elseif (is_null($this->_value)) {
return $this->_value;
}
$temp = $this->_refresh($temp, $pos, $arg, $this->_value);
} while(count($temp) > 1);
$this->_value = $temp[0];
$time2 = $this->_getMicroTime();
$this->_timer = $time2 - $time1;
return $this->_value;
}
