Number rounding and precision problems in XSLT 1.0

Question

I have an inconsistency while using xsl,

here is the xml,

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

and xsl,

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:fo="http://www.w3.org/1999/XSL/Format">
    <xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
    <xsl:template match="/">
        <TotalAmount>
            <xsl:value-of select="Rate/TotalRate + Rate/TotalTax"/>
        </TotalAmount>
    </xsl:template>
</xsl:stylesheet>

and the output is,

<TotalAmount xmlns:fo="http://www.w3.org/1999/XSL/Format">523.4100000000001</TotalAmount>

but the expected o/p is,

<TotalAmount xmlns:fo="http://www.w3.org/1999/XSL/Format">523.41</TotalAmount>

Why the o/p is 523.4100000000001? how can i get 523.41 without rounding it?

Answer 1

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>