Re: Sizeof int_fastN_t vs uint_fastN_t data types

[Martin Husemann <martin%duskware.de@localhost>]

On Mon, Nov 18, 2024 at 09:00:59AM +0000, Sad Clouds wrote:
> I would expect discrepancy between OSes, e.g. Linux aarch64 defines
> fast versions for 16 and 32 bit integers at 8 bytes, NetBSD aarch64
> defines fast versions for 16 and 32 bit integers at 4 bytes. However,
> the same OS defining different sizes for signed and unsigned fast
> integers seems a bit strange. Is there really that much overhead for
> signed integer arithmetic on sparc64?

Registers are 8 byte and sign extension is (relatively) expensive.
There are only native arithmetic instuctions for 4 byte and 8 byte
values (and the 4 byte versions may still need sign extension at the
end).

You can try and look at the differences in the assembler code generated
for _fast vs. non-fast variants of the same code. Compilers have gotten
incredible smart and I would expect the optimized code to be not much
different in most cases, but it would be interesting to compare that for some
real-world cases where the _fast variants are used.

Martin