Re: [PATCH v4 1/5] sim: cgen: add remainder functions (needed for OR1K lf.rem.[sd])

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2017-09-01 00:33, Stafford Horne wrote:
>> I can't tell for sure because I'm not maintainer of sim/, but I 
>> suppose that
>> we would need a proper implementation that doesn't use the host fpu 
>> here.
> 
> Right, as mentioned in the summary, this is the one place that is a bit
> controversial.
> 
> I was thinking its kind of strange to not allow using libmath, since
> integer math runs on the host system, why not FPU as well?
> (probably to implement this I would just copy from libmath in the end:)

That was just my conclusion after reading the comment in sim-fpu.h:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=sim/common/sim-fpu.h;h=d27d80a513aa8d996a7b4c6af53fde31dcb8dad7;hb=HEAD#l54

It is easy for floating point unit implementations to return wrong or 
slightly different results.  Integer math is more consistent.

> https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=sysdeps/ieee754/dbl-64/e_remainder.c;hb=HEAD
> 
> There are actually no OpenRISC cores that implement the remainder
> instruction (as its a bit complicated to do in hardware and not really 
> used
> much). I could remove it if the implementation is beyond the scope of 
> this
> series.

Indeed, it can always be contributed later.

Simon