On Nov 23, 7:43 pm, "Jason Martin" <[EMAIL PROTECTED]> wrote: > Well, after a bit more reading, I now think that bitwise shifting is > available. I was confused because all the floating point operations > are explicitly listed whereas for the integer operations only the > "atomic" operations are listed. But, "atomic" just appears to be a > memory-locking operation. On page 50 of the CUDA programming guide > they use a bitwise right shift to demonstrate fast division by 2, so > clearly it's supported (and takes 4 clock cycles).
CUDA hardware can be programmed in PTX assembly language, as well as in CUDA's C-like language. PTX isn't quite a real assembly language; the assembler handles register allocation, for instance, and several "instructions" are actually synthesized from simpler instructions. But it's much closer to the hardware than CUDA, so it gives a much better idea of what the hardware can really do. You can get the PTX reference manual in the CUDA SDK's. (I've also put a copy at http://sage.math.washington.edu/home/cwitty/ptx_isa_1.2.pdf .) If you read through the PTX reference manual, you see that the processor does have a full complement of integer instructions. However, the 32-bit multiply is apparently synthesized from 24-bit multiplies, which are also directly available: there are two 24x24->32 multiply instructions. One returns the low 32 bits of the 48-bit result, the other returns the high 32 bits (so there's a 16-bit overlap between these results). My guess, then, is that CUDA would work best with 24-bit limbs (packed in 32-bit words). Also, for MPIR, it would probably be better to program directly in PTX. (And there's also a note that says that on CUDA hardware that supports 32-bit multiplies, the 32-bit multiply instruction will be fast and the 24-bit multiply instructions may be slow. I don't know if such hardware exists yet, but eventually you might need two CUDA branches, one with 24-bit limbs and one with 32-bit limbs.) Carl --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "mpir-devel" group. To post to this group, send email to mpir-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/mpir-devel?hl=en -~----------~----~----~----~------~----~------~--~---
