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* q8_k_r8: fastest matrix multiplication known to human kind We get PP-512(LLaMA-3.1-8B) = 370 t/s on a Ryzen-7950X! * q8_k_r8: AVX2 I was worried that we don't have enough vector registrers on AVX2, but it looks like it handles it just fine. We get PP-512(LLaMA-3.1-8B) = 354 t/s on a Ryzen-5975WX. Slightly slower than the Zen4 version with double the threads, but still a huge upgrade compared to Q8_0_R4. * q8_k_r4: NEON We get PP-512(LLaMA-3.1-8B) = 159.2 t/s. Compare this to the 128 t/s we have fr Q8_0_R4. * q8_k_r4: go to signed ints Why? * On AVX2 _mm256_maddubs_epi16() may overflow, so we need to stay within the signed int range and use _mm256_sign_epi8. Not yet tested on the AVX2 comp, vut expect major slowdown. * It is almost 10% faster on ARM_NEON. Somehow the veorrq_u8() needed tto convert from unsigned to signed seems to be extremely slow on the M2-Max * We only lose ~0.5% in oerformance on Zen4 (there the exclusive or that we now use to convert fro signed to unsigned seems to be much faster than on M2-Max) * Shutup useless compiler warnings --------- Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>