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Re: RFC: Creating a more efficient sincos interface

On 09/13/2018 03:27 PM, Wilco Dijkstra wrote:

The existing sincos functions use 2 pointers to return the sine and cosine result. In
most cases 4 memory accesses are necessary per call. This is inefficient and often
significantly slower than returning values in registers. I ran a few experiments on the
new optimized sincosf implementation in GLIBC using the following interface:

__complex__ float sincosf2 (float);

This has 50% higher throughput and a 25% reduction in latency on Cortex-A72 for
random inputs in the range +-PI/4. Larger inputs take longer and thus have lower
gains, but there is still a 5% gain on the (rarely used) path with full range reduction.
Given sincos is used in various HPC applications this can give a worthwile speedup.

I think this is totally fine if you call it expif or something like that (and put the sine in the imaginary part, of course).

In general, I would object to using complex numbers for arbitrary pairs, but this doesn't apply to this case.


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