[R-pkg-devel] Use of long double in configuration

[Uwe Ligges]

On 30.04.2025 10:25, Tim Taylor wrote:
> Is it correct to say that R's conditional use of long double is around ensuring things work on platforms which have 'long double' identical to 'double' types, as opposed to there being an odd compiler targeted that does not even have any concept of 'long double' type?

a double is 64 bit and stored that way on all platforms, the concept of 
long doubles is CPU specific. x86 chips have 80bit in the floating point 
units for calculations before rounding (and normalizing) to a regular 
double.

Some chips, e.g. those ARM chips used in current M[123]Macs (hence very 
relevant topic), do not support long doubles. And compilers offer to 
compile without support for long doubles which e.g. CRAN uses to check 
in an additional (issues) check.

Best,
Uwe Ligges

> 
> As background this was motivated by a query raised in the matrixStats package:
> https://github.com/HenrikBengtsson/matrixStats/issues/278
> 
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