Why those particular integer multiplies?

The x86 instruction set has a range of unique SIMD integer multiply operations, deeply rooted in the architecture since the Pentium MMX era. The post explores the implementation and idiosyncrasies of these operations across different iterations, including MMX, SSE, SSE2, SSSE3, SSE4.1, and AVX-512. It delves into specifics of commands like PMULLW, PMULHW, PMADDWD, and others, detailing their purposes, historical context, and technical intricacies. The discussion also touches on the evolution of these operations and how Intel and AMD have adapted their multiplier designs over time.