Calculating Sum in XSLT 1.0

I am trying to generate a sum of attribute values of
sibling nodes via XSLT 1.0

My XML looks like this

<sibling value="5"/>
<sibling value="7">
<sibling value="9">
<sibling value="13">
<currentnode>some text</currentnode>

When I am processing the template for currentnode I
want to calculate the sum of the "value" attribute of
all its previous sibling nodes i.e. I want to find the
sum of 5,7,9 and 13. The names of the sibling node and
current node are different. 
I know there isn't a direction function to do this. If
anyone has written template or come accross the
problem then please let me know how did you solve it. 
Thank you for your help and Merry Christmas.
Abhi



		
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