XSLT Cookbook

Implementing Common Math Functions

Problem

You need to go beyond fifth-grade math even though XSLT 1.0 does not.

Solution

Pure XSLT implementations are provided for absolute value, square root, logarithms, power, and factorial.

Absolute value: math:abs(x)

The obvious but long-winded way to determine the absolute value of a number is shown here:

<xsl:template name="math:abs">
     <xsl:param name="x"/>
     
     <xsl:choose>
          <xsl:when test="$x &lt; 0">
               <xsl:value-of select="$x * -1"/>
          </xsl:when>
          <xsl:otherwise>
               <xsl:value-of select="$x"/>
          </xsl:otherwise>
     </xsl:choose>
     
</xsl:template>

The short but obscure way relies on the fact that the true always converts to the number 1 and false to the number 0.

<xsl:template name="math:abs">
     <xsl:param name="x"/>
     <xsl:value-of select="(1 - 2 *($x &lt; 0)) * $x"/>
</xsl:template>

I prefer the latter because it is concise. Alternatively, you can use an extension function (see Chapter 12).

Square root: math:sqrt(x)

Nate Austin contributed a native XSLT sqrt to EXSLT that uses Newton’s method:

<xsl:template name="math:sqrt"> <!-- The number you want to find the square root of --> <xsl:param name="number" select="0"/> <!-- The current 'try'. This is used internally. --> <xsl:param name="try" select="1"/> <!-- The current iteration, checked against maxiter to limit loop count --> <xsl:param name="iter" select="1"/> <!-- Set this up to ensure against infinite loops --> <xsl:param name="maxiter" select="20"/> <!-- This template was written by Nate Austin using Sir ...