Number rounding and precision problems in XSLT 1.0

In XSLT 1.0 numbers are implemented with the double type and as with any binary floating-point type, there is a loss of precision.

In XSLT 2.0/XPath 2.0 one can use the xs:decimal type to work without loss of precision.

I. XSLT 1.0 solution:

Use the format-number() function:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">    <xsl:output omit-xml-declaration="yes" indent="yes"/>    <xsl:template match="/*">        <TotalAmount>      <xsl:value-of select="format-number(TotalRate + TotalTax, '0.##')"/>              </TotalAmount>    </xsl:template></xsl:stylesheet>

When this transformation is applied on the provided XML document:

<Rate>    <TotalRate>506.41</TotalRate>    <TotalTax>17</TotalTax>    <Currency>INR</Currency></Rate>

the wanted, correct result is produced:

<TotalAmount>523.41</TotalAmount>

Here is also an example, showing that the wanted precision maynot be statically known and could be passed to the transformation as an external/global parameter:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">    <xsl:output omit-xml-declaration="yes" indent="yes"/>    <xsl:param name="pPrec" select="2"/>    <xsl:param name="pPrec2" select="13"/>    <xsl:variable name="vPict" select="'##################'"/>    <xsl:template match="/*">        <TotalAmount>      <xsl:value-of select=      "format-number(TotalRate + TotalTax,                     concat('0.', substring($vPict,1,$pPrec))                     )"/>        </TotalAmount>        <TotalAmount>      <xsl:value-of select=      "format-number(TotalRate + TotalTax,                     concat('0.', substring($vPict,1,$pPrec2))                     )"/>        </TotalAmount>    </xsl:template></xsl:stylesheet>

When this transformation is applied on the provided XML document, two results are produced -- with precision 2 and precision 13:

<TotalAmount>523.41</TotalAmount><TotalAmount>523.4100000000001</TotalAmount>

II. XSLT 2.0 solution using xs:decimal:

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs"> <xsl:output omit-xml-declaration="yes" indent="yes"/> <xsl:strip-space elements="*"/> <xsl:template match="/*">        <TotalAmount>      <xsl:value-of select="xs:decimal(TotalRate) + xs:decimal(TotalTax)"/>        </TotalAmount> </xsl:template></xsl:stylesheet>

When this transformation is applied on the same XML document (above), the wanted, correct result is produced:

<TotalAmount>523.41</TotalAmount>