coding in xslt - adding two values together, but only using the first 8 characters of the value

I am creating a hash off of account numbers.   using xslt, can someone help code the following?

the two account numbers i need added up are

192937465
and
123456789
the value the following code produces is 316,294,254

this is the value of the two account numbers if you take in the full 9 digit account number and use it in the summing equation.
i need for the xlst code to take the two account numbers and only add the first 8 digits of the accountnumber together together.
12345678 and 19283746 which would equal 31,629,424

the xlst code i currently have in place is

XSLT:
<xsl:variable name="ENTRYHASH">
        <xsl:call-template name="prepend-pad">
          <xsl:with-param name="padVar" select = "number(sum( /ACCOUNT/ACCOUNTNUMBER ))"/>
        </xsl:call-template>
      </xsl:variable>