Saxonica SaxonCS-HE 13 RNG repro

Summary

This repository reproduces an issue in SaxonCS-HE 13 where random-number-generator() appears to produce different results across runs when seeded with xs:dateTime, even when the seed value is fixed.

Expected behavior

Using the same seed value should produce the same random sequence across separate executions.

Actual behavior

When the seed is provided as xs:dateTime, the generated value changes between runs. When the same timestamp is provided as a string seed, the generated value remains stable between runs. This means that the same logical timestamp value leads to different results depending on whether it is passed as xs:dateTime or as a string.

Setup

• .NET 10.0
• SaxonCS-HE 13.0
• OS: Windows 11 25H2 x64

Reproduction

1. Run dotnet run.
2. Note the generated values.
3. Run dotnet run again.
4. Compare the outputs.

Test setup details

The XSLT document contains three variants:

1. current-dateTime() as seed (pinned by the host application)
2. constant xs:dateTime as seed
3. string(current-dateTime()) as seed

To eliminate runtime clock differences, the current date/time is pinned using Saxon.Hej.Controller.setCurrentDateTime().

All variants effectively use the same timestamp value: 2025-02-16T09:35:47Z

Sample output

The values for random-constDateTime and random-currentDateTime change across runs, while random-stringDateTime remains stable.

Run 1

random-currentDateTime 1:	59300
random-currentDateTime 2:	59300
random-currentDateTime 3:	59300
random-constDateTime 1:		59300
random-constDateTime 2:		59300
random-constDateTime 3:		59300
random-stringDateTime 1:	59894
random-stringDateTime 2:	59894
random-stringDateTime 3:	59894

Run 2

random-currentDateTime 1:	52993
random-currentDateTime 2:	52993
random-currentDateTime 3:	52993
random-constDateTime 1:		52993
random-constDateTime 2:		52993
random-constDateTime 3:		52993
random-stringDateTime 1:	59894
random-stringDateTime 2:	59894
random-stringDateTime 3:	59894

Additional context

For comparison, the same scenario previously behaved deterministically in SaxonHE10Net31Api by Martin Honnen. After migrating the project to .NET 10.0, all tests were still passing. The changed behavior appeared only after switching to the official Saxon 13 library.

I understand that this older library is unrelated to SaxonCS and that its behavior is not necessarily intended here. However, since the RNG is documented as deterministic, and since a string seed produces stable values across runs, I would expect a constant xs:dateTime seed to behave consistently as well.