Implementation of "str:align" seems to be wrong

I'm stepping through the regression tests for EXSLT functions.  I was
looking at the "str:align" function.  The Xalan-native implementation,
and the implementation in the EXSLT library, seem to be slightly wrong.

>From how I understand what the function should do, it essentially
superimposes the target string on top of the padding string.  The
resulting string length should be the max of the target and padding
string lengths.

In the "left" case, the following is directly from the implementation:

  <func:result select="concat($string, substring($padding, $str-length +
1))" />

This concatenates the target string with the padding, taking the length
of the padding string as the length of the TARGET string.  Therefore, if
the target string is length 21 and the padding is length 30, the
resulting string will be length 42, instead of 30, as I believe it
should be.  I guess this line should actually be (guessing):

  <func:result select="concat($string,substring($padding,($pad-length -
$str-length)))"/>