Numerical accuracy of SIMD primitives
Hardware vector arithmetic (SIMD)

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No guarantees are made that math.vectors.simd words will give identical results on different SSE versions, or between the hardware intrinsics and the software fallbacks.

In particular, horizontal operations on float-4 vectors are affected by this. They are computed with lower precision in intrinsics than the software fallback. Horizontal operations include anything involving adding together the components of a vector, such as sum or normalize.