Rounding error in a sum

[fagertjan]

Hi,

I am busy with a peppol/ubl implementation and am using your command line tool to verify my generated xml against the schematron. It works fine in most cases but for one file I get a failure caused by a rounding error. The rule that fails checks if some sum is the same as a value stated elsewhere in the file. See: https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/BR-AE-08/

The schematron states that the values are xs:decimal, but it seems that native javascript is being used. If I do 24.63 + 62.16 in the console of my browser I also get a rounding error: 86.78999999999999.

I created a sample that does the same calculation.

Sample xml:

<?xml version="1.0"?>
<Invoice>
  <Total>
    86.79
  </Total>
  <Lines>
    <Line>
      <SubTotal>
        24.63
      </SubTotal>
    </Line>
    <Line>
      <SubTotal>
        62.16
      </SubTotal>
    </Line>
  </Lines>
</Invoice>

Sample schematron:

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2">
  <ns prefix="xs"  uri="http://www.w3.org/2001/XMLSchema"/>

  <pattern id="ubl-model">
    <rule context="/*">
      <assert test="(xs:decimal(Total) = sum(Lines/Line/xs:decimal(SubTotal)))">
        <value-of select="xs:decimal(Total)" /> is not the same as <value-of select="sum(Lines/Line/xs:decimal(SubTotal))" />
      </assert>
    </rule>
  </pattern>
</schema>

The failed assertion of my sample says:
asrt ✘ 86.79 is not the same as 86.78999999999999

Regards,
Gert Jan

[wvbe]

Hey Gert Jan, sorry for the inconvenience. Correct, this lib uses native JS maths for all things.

Off the top of my head I don't know how to get Javascript to behave more nicely when it comes to rounding etc. without using a new dependency. IMHO it should take some research one that is appropriate and minimal.

If you have any suggestions, please let me know. I'm happy to make a change if it is easy, but I'll admit that my activity on node-schematron has dropped to near zero.

Also, thanks for reporting!

[yokrysty]

i use this code at my program entry

(1.005).toFixed(2) === '1.01' || (function(prototype) {
    const toFixed = prototype.toFixed;
    prototype.toFixed = function(fractionDigits) {
        const str = this + '';
        const parts = str.split('.');
        const num = parts.length === 2 && parts[1].length >= fractionDigits ? +(str + '1') : this;
        return toFixed.call(num, fractionDigits);
    }
    console.log('polyfill used for .toFixed()');
}(Number.prototype));