I have seen that SiSoft Sandra has built-in tests for double precision on GPU even on cards that do not support it. It most likely uses some OpenCL library that does 64 bit calculations on 32-bit hardware.
Am I mistaken that this sort of behavior could be achieved if only the very basic operations (ADD, MUL, FMAD...) and the likes are implemented on ISA level and let everything automatically build on top of that with already existing software? Compute power drops about 10X on my Mobility 5870, which is still quite good.
Would AMD implement pseudo DP on all their cards to enable developers to test DP applications on their mobile workstations as well? It is a really big pain to have to implement everything twice, #define REAL float/double everywhere and then use sizeof(REAL) everywhere. I would much more welcome some standard way of having DP on all HW.
This could be some vendorspecific extension.
(Edit: I just figured this would fit better into another topic. I'll summarize there also)