drotg implementation is not up to date with the reference BLAS

[vladimir-ch]

The Reference BLAS changed their DROTG implementation in Reference-LAPACK/lapack#527 to use a safe scaling. In Gonum we updated our implementation and tests accordingly in gonum/gonum#1623. Unfortunately, the updated tests with extreme values fail in our CBLAS interface package (gonum/netlib#92) where we use OpenBLAS as a reference. It would be nice if OpenBLAS used the same implementation with safe scaling as the reference BLAS.

[angsch]

The same problem will likely trigger for NRM2. As far as I am aware, the assembly implementations in OpenBLAS have not been updated. I think that changing all assembly implementations is a challenge, so one option may be to add an additional symbol, one for the netlib implementation and one for the old optimized implementation.

[martin-frbg]

Pretty much the only somewhat short-term solution I see is to update the "generic" reimplementations and "temporarily" use them for all architectures/cpus that have hand-crafted assembly now

[martin-frbg]

Small clarification - ?ROTG is easy as it is all done in trivial C code in the interface routine, no cpu-specific kernels involved. NRM2 will require a bit more work as there are around 50 assembly kernels in all (and still about 10 if only looking at the most important ones)