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Among the deficiencies are lack of division and modulus operations, an inability to produce the high-order word of a 32-bit multiply, extremely poor carry propagation (add with carry, subtract with borrow) support, and the lack of unsigned arithmetic operations.
Please can these be addressed in the next release of the architecture? For the moment, only GPUs and the Xeon Phi are of much use for parallel integer arithmetic.
FWIW, my Parallella cluster is doing useful work with elliptic curve arithmetic but it is running purely on the ARM cores. I plan to try porting it to the Epiphany but I've already decided that a radically unusual approach will be essential. The residue number system (RNS) representation of multi-precise integers has carry-free arithmetic. Multiprecision modular remainder doesn't require division or modulo operators because Montgomery reduction is possible (that's true of regular representation too). The sticking point is 32*32=>64 multiplication and 64/32 => 32q/32r division/modulus. For a start, lack of unsigned arithmetic reduces those 64s to 62 and the 32s to 31. Lack of division for the RNS primitives can be worked around, by careful shifts and subtractions, will still be more expensive than would be desirable.
Statistics: Posted by xilman — Thu Nov 20, 2014 11:44 am
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I think I'm bottlenecked by getting the data back from the Epiphany to the ARM. The e-bandwidth-test example returns:
ARM Host --> eCore(0,0) write spead = 13.68 MB/s
ARM Host --> eCore(0,0) read spead = 6.55 MB/s
ARM Host --> ERAM write speed = 75.77 MB/s
ARM Host <-- ERAM read speed = 105.69 MB/s
ARM Host <-> DRAM: Copy speed = 195.37 MB/s
eCore (0,0) --> eCore(1,0) write speed (DMA) = 1280.04 MB/s
eCore (0,0) <-- eCore(1,0) read speed (DMA) = 390.01 MB/s
eCore (0,0) --> ERAM write speed (DMA) = 240.24 MB/s
eCore (0,0) <-- ERAM read speed (DMA) = 87.61 MB/s
The core are doing DMA writes to ERAM, then the ARM is reading, so I think I should max out at 73 MB/s at best, I get 60% of that. But I also have the synchronisation in ERAM in between those calls
Update: The ARM copy-back with e_read() is 95% of the visible time...
Statistics: Posted by Melkhior — Thu Nov 20, 2014 8:01 am
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