Symphony.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template name="ConvertDecToHex">
    <xsl:param name="index" />
    <xsl:if test="$index > 0">
      <xsl:call-template name="ConvertDecToHex">
        <xsl:with-param name="index" select="floor($index div 16)" />
      </xsl:call-template>
      <xsl:choose>
        <xsl:when test="$index mod 16 &lt; 10">
          <xsl:value-of select="$index mod 16" />
        </xsl:when>
        <xsl:otherwise>
          <xsl:choose>
            <xsl:when test="$index mod 16 = 10">A</xsl:when>
            <xsl:when test="$index mod 16 = 11">B</xsl:when>
            <xsl:when test="$index mod 16 = 12">C</xsl:when>
            <xsl:when test="$index mod 16 = 13">D</xsl:when>
            <xsl:when test="$index mod 16 = 14">E</xsl:when>
            <xsl:when test="$index mod 16 = 15">F</xsl:when>
            <xsl:otherwise>A</xsl:otherwise>
          </xsl:choose>
        </xsl:otherwise>
      </xsl:choose>
    </xsl:if>
  </xsl:template>

</xsl:stylesheet>