Explicitly use floor instead of casting to int. Protects against changes to FPU rounding mode
Cosmetics
Use _mm256_madd_epi16 (VPMADDW) in AVX2 horizontal u16 resizer core. Improvement of 30% on lanzos4, 40% on downscaling
Use _mm256_madd_epi16 in AVX2 vertical u16 core. Improvement of 70% on
lanczos4, 40% on downscaling