fontoxpath-exact-decimal

Temporary fork of fontoxpath 3.34.0 with exact xs:decimal arithmetic. It exists only until FontoXML/fontoxpath#686 is fixed upstream, and will be deprecated in favour of upstream the moment it is.

Why

Stock fontoxpath computes xs:decimal arithmetic in float64, which violates XPath decimal semantics:

evaluateXPath('1.1 + 2.2 = 3.3')  // stock: false — this fork: true

This breaks real-world users of decimal arithmetic — e.g. the EN 16931 e-invoicing Schematron rules, where a compliance validator flags valid invoices (rule BR-O-08 on the official CEF example XRechnung-O.xml).

What changed

One bounded patch to the dist bundles (dist/fontoxpath.js, dist/fontoxpath.esm.js): in the numeric binary-operation dispatch, when the result type resolves to xs:decimal/xs:integer — i.e. both operands are decimal subtypes — + − × div are computed exactly (BigInt over the scaled decimal representation). Untyped/double/float operands keep IEEE 754 float semantics, as the spec requires (0.1 + 0.2e0 is still 0.30000000000000004).

Everything else is byte-identical to fontoxpath 3.34.0. Known limitation: aggregates (fn:sum, fn:avg) still accumulate in float64 — the full fix needs an exact decimal value representation upstream.

Usage

Drop-in replacement via package alias:

{ "dependencies": { "fontoxpath": "npm:[email protected]" } }

License

MIT, same as upstream — see LICENSE.md (© Fonto Group BV, Martin Middel; patch © NeosiaNexus).