subtraction of exact CQL Quantities

[randolphbarrows]

Using cql-execution v3.3.0 from 8/2025, subtraction of exact CQL Quantities 1.4 'mg/dL' - 0.3 'mg/dL' evaluated to 1.0999999999999999 'mg/dL', causing a subsequent comparison with 1.1 'mg/dL' to fail. Notably, this works as expected in the CQF CQL Extension.

Perhaps this is related to Issue 280 'Improve support for CQL Decimal' from 10/2022 (i.e. "Initial precision is not maintained in all cases")?

[cmoesel]

Yes, this related to #280 in that it stems from the problem that JavaScript Numbers are double-precision floating-point numbers, and therefore suffer from some of the inherent quirks of floating-point numbers.

I tested this using the Node command-line replicator and confirmed it for this specific calculation:

That said, I thought that we rounded values to 8 decimal places before doing comparisons, but perhaps I am mistaken (based on your report). Do you think that would be a reasonable workaround for this issue (until we can integrate a more precise number library)?

[randolphbarrows]

Thank you, Chris. Yes, I expect rounding to 8 decimal places is adequate for almost all clinical computing needs, certainly ours, and rounding to even fewer decimal places is the workaround in our code.