Summary This is an XSLT implementation of a function that calculates a^b (a to the power of b) for any positive integer base a and any integer power b.

The source code is self-explanatory. This is a typical recursive template. Do notice how the factor and increment are established according to whether pow is non-negative or negative.

Also, be aware that deep recursive processing will crash your MSXML -- I succeeded with base=1 and pow=10000 on a 128MB RAM P-266 computer. In this case MSXML crashed in about 30 seconds.

On the same computer with my ol' Saxon 4.6 the correct value was calculated for about 5 seconds.

Here's a sample xml source and the stylesheet -- when applied the result is:

0.008

Note also, that in a production environment system there should be some validation added to ensure that a and b have correct (permissible) values.

Source xml:
-------------

Stylesheet:
------------
<xsl:stylesheet version=1.0>
    <xsl:output method=text/>

    <xsl:template match=/>
        <xsl:call-template name=pow>
            <xsl:with-param name=base select=/power/base/>
            <xsl:with-param name=pow select=/power/pow/>
        </xsl:call-template>
    </xsl:template>

    <xsl:template name=pow>
        <xsl:param name=base select=1/>
        <xsl:param name=pow select=0/>
        <xsl:param name=tmpResult select=1/>

        <xsl:variable name=result>
            <xsl:choose>
                <xsl:when test=$pow >= 0>
                    <xsl:value-of select=$tmpResult * $base/>
                </xsl:when>
                <xsl:otherwise>
                    <xsl:value-of select=$tmpResult div $base/>
                </xsl:otherwise>
           </xsl:choose>
        </xsl:variable>

        <xsl:variable name=incr>
            <xsl:choose>
                <xsl:when test=$pow >= 0>
                    <xsl:value-of select=- 1/>
                </xsl:when>
                <xsl:otherwise>
                    <xsl:value-of select=1/>
                </xsl:otherwise>
            </xsl:choose>
        </xsl:variable>

        <xsl:choose>
            <xsl:when test=$pow = 0>
                <xsl:value-of select=$tmpResult/>
            </xsl:when>
            <xsl:otherwise>
                <xsl:call-template name=pow>
                    <xsl:with-param name=base select=$base/>
                    <xsl:with-param name=pow select=$pow + $incr/>
                    <xsl:with-param name=tmpResult select=$result/>
                </xsl:call-template>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:template>
</xsl:stylesheet>

Additional information

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="text"/> <xsl:template match="/"> <xsl:call-template name="pow"> <xsl:with-param name="base" select="/power/base"/> <xsl:with-param name="pow" select="/power/pow"/> </xsl:call-template> </xsl:template> <xsl:template name="pow"> <xsl:param name="base" select="1"/> <xsl:param name="pow" select="0"/> <xsl:param name="tmpResult" select="1"/> <xsl:variable name="result"> <xsl:choose> <xsl:when test="$pow >= 0"> <xsl:value-of select="$tmpResult * $base"/> </xsl:when> <xsl:otherwise> <xsl:value-of select="$tmpResult div $base"/> </xsl:otherwise> </xsl:choose> </xsl:variable> <xsl:variable name="incr"> <xsl:choose> <xsl:when test="$pow >= 0"> <xsl:value-of select="- 1"/> </xsl:when> <xsl:otherwise> <xsl:value-of select="1"/> </xsl:otherwise> </xsl:choose> </xsl:variable> <xsl:choose> <xsl:when test="$pow = 0"> <xsl:value-of select="$tmpResult"/> </xsl:when> <xsl:otherwise> <xsl:call-template name="pow"> <xsl:with-param name="base" select="$base"/> <xsl:with-param name="pow" select="$pow + $incr"/> <xsl:with-param name="tmpResult" select="$result"/> </xsl:call-template> </xsl:otherwise> </xsl:choose> </xsl:template> </xsl:stylesheet>