[gmx-developers] mknb doesn't work on BlueGene with --enable-ppc-sqrt in single precision

[Mark Abraham]

Hi,

After "./configure --enable-ppc-sqrt" on BlueGene, mknb is called with 
-ppc_sqrt. In ppc_invsqrt(), mknb_innerloop.c generates code to call to 
__frsqrtes. That might be sound on other PPC architectures, but BlueGene 
doesn't do single-precision arithmetic, so this built-in does not exist.

To work-around, do not specify --enable-ppc-sqrt in single precision on 
BlueGene.

To fix, we would still prefer to use the PPC inverse square root in all 
cases. We need to call a double-precision version on BlueGene, and not 
on others. That suggests mknb_innerloop.c needs to #include <config.h> 
(which is on the search path) and use #ifdef GMX_BLUEGENE.

(If Bugzilla was working, I'd have filed this and various others of my 
reports on Bugzilla. How do we make sure these get dealt with for any 
4.0.6 release?)

Mark