Possible RISC-V Vector Instructions missing


Tony Cole
 

Hi Vector Team,

 

I’m new to RISC-V and the Vector extensions, so forgive me if I’ve missed something.

 

 

I have searched the specs, emails and git hub issues, but not found anything on this:

 

 

While writing some vector code using the vector intrinsics, I noticed some instructions missing that I expected to see:

 

I noticed there is no saturated reverse subtract version of vssub_vx, e.g. vsrsub_vx (or should it be vrssub_vx ?) and so no vsneg_v pseudo instructions

 

But there are the following integer/float reverse subtract instructions:

vrsub_vx

vfrsub_vf

 

and their pseudo instruction counterparts:

vneg_v

vfneg_v

 

For orthogonality there should be saturated versions of the above, but maybe there is not enough encoding space?

Or possibly remove vrsub_vx & vfrsub_vf to gain encoding space ??

 

Note: I wanted to use vsrsub_vx (to do vsneg_v), but instead achieved it by loading a vector with zero and performing vssub_vv.

 

Tony Cole

CPU Consultant I RISC-V Cores, Bristol

E-mail: Tony.Cole@...

Company: Huawei technologies R&D (UK) Ltd I Address: 290 Park Avenue, Aztec West, Almondsbury, Bristol, Avon, BS32 4SY, UK      

 

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