Is it possible to cast floats directly to __m128 if they are 16 byte aligned?

c++ c alignment sse intrinsics
dtech picture dtech · Aug 1, 2012 · Viewed 10.6k times · Source

Is it safe/possible/advisable to cast floats directly to __m128 if they are 16 byte aligned?

I noticed using _mm_load_ps and _mm_store_ps to "wrap" a raw array adds a significant overhead.

What are potential pitfalls I should be aware of?

EDIT :

There is actually no overhead in using the load and store instructions, I got some numbers mixed and that is why I got better performance. Even thou I was able to do some HORRENDOUS mangling with raw memory addresses in a __m128 instance, when I ran the test it took TWICE AS LONG to complete without the _mm_load_ps instruction, probably falling back to some fail safe code path.

Answer

Paul R picture Paul R · Aug 1, 2012

What makes you think that _mm_load_ps and _mm_store_ps "add a significant overhead" ? This is the normal way to load/store float data to/from SSE registers assuming source/destination is memory (and any other method eventually boils down to this anyway).

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