tdf#129606 move approxDiff to rtl::math and fix ARM64 rounding errorsHEADmaster

Move the approxDiff heuristic from the sc unnamed namespace to rtl::math and
disable floating-point contraction (FMA) for this function.

On ARM64 (Apple Silicon), the use of Fused Multiply-Add (FMA) results in
higher intermediate precision during floating-point operations. While
mathematically more accurate, this prevents legacy rounding heuristics in
approxDiff and approxValue from detecting and cleaning rounding artifacts
in series generation (e.g., 1.1 - 1.0).

Disabling fp-contract forces intermediate rounding to 64-bit IEEE 754
limits. This ensures the noise expected by the approximation logic is
present, restoring consistency with x86-64 behavior and fixing issues where
values like 6.0 are incorrectly rendered as 6.00000000000001.

Change-Id: I54a0f748be6cf817db1f3bdcfd2b355320c3a617
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/203233
Reviewed-by: Dan Williams <dcbw@libreoffice.org>
Tested-by: Jenkins

0 files changed, 0 insertions, 0 deletions