Implementations of SIMD instruction sets for systems which don't
natively support them.

The SIMDe header-only library provides fast, portable implementations of
SIMD intrinsics on hardware which doesn't natively support them, such as
calling SSE functions on ARM. There is no performance penalty if the
hardware supports the native implementation (e.g., SSE/AVX runs at full
speed on x86, NEON on ARM, etc.).
