strtr和str_replace效率探索

今天写代码用到字符串规制，就上网查了下strtr与str_replace的效率如何，网上一些地方说strtr比str_replace快四倍。半信半疑，自己就做了下测试。

strtr比较怪异，用法这里不提。只做两种这两个函数可以替换用的测试例子。

第一种

list( $usec, $sec ) = explode(' ', microtime() );
$star = $usec+$sec;
$string = 'paocaiasdfsadfasdfasdfasdfasdfasdfasdfasdfasdfpaocaiasdfsadfasdfasdfasdfasdfasdfasdfasdfasdfpaocaiasdfsadfasdfasdfasdfasdfasdfas!';
$aa = array('pao'=>'a');
for($i=1; $i<= 10000; $i++ ){
 $sssss = strtr( $string, $aa ); 
}
list( $usec, $sec ) = explode(' ', microtime() );
$end = $usec+$sec;
echo 'strtr用时：'.($end-$star);
echo "
";

list( $usec, $sec ) = explode(' ', microtime() );
$star = $usec+$sec;
for($i=1; $i<= 10000; $i++ ){
 $sssss = str_replace('pao', 'a', $string ); 
}
list( $usec, $sec ) = explode(' ', microtime() );
$end = $usec+$sec;
echo 'str_replace用时：'.($end-$star);
echo "
";
exit;

结果如下：

strtr用时：0.10797691345215

str_replace用时：0.020326137542725

第二种

$string = 'absdfddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd';

list( $usec, $sec ) = explode(' ', microtime() );
$star = $usec+$sec;
for($i=1; $i<= 100000; $i++ ){
 $sssss = strtr( $string, 'ab', '01');
}
list( $usec, $sec ) = explode(' ', microtime() );
$end = $usec+$sec;
echo 'strtr用时：'.($end-$star);
echo "
";

list( $usec, $sec ) = explode(' ', microtime() );
$star = $usec+$sec;
for($i=1; $i<= 100000; $i++ ){
 $sssss = str_replace( 'ab', '01', $string);
}
list( $usec, $sec ) = explode(' ', microtime() );
$end = $usec+$sec;
echo 'str_replace用时：'.($end-$star);
echo "
";
exit;

结果如下：

strtr用时：0.20317006111145
str_replace用时：0.14615988731384

以上两个测试用时，随着$string变大和for循环变大，strtr用时会比str_replace用时越来越多，for循环达到百万级时，strtr用时是str_replace用时的四倍，无语了。

以下是strtr源码，可能strtr在其他使用例子上是比较快，但是不能和str_replace做比较。

/* {{{ php_strtr
 */
PHPAPI char *php_strtr(char *str, int len, char *str_from, char *str_to, int trlen)
{
    int i;
    unsigned char xlat[256];
 
    if ((trlen < 1) || (len < 1)) {
        return str;
    }
 
    for (i = 0; i < 256; xlat[i] = i, i++);
 
    for (i = 0; i < trlen; i++) {
        xlat[(unsigned char) str_from[i]] = str_to[i];
    }
 
    for (i = 0; i < len; i++) {
        str[i] = xlat[(unsigned char) str[i]];
    }
 
    return str;
}
/* }}} */