x64 Assembly Tutorial 42: MMX Multiplication Instructions скачать в хорошем качестве

x64 Assembly Tutorial 42: MMX Multiplication Instructions

This tutorial is about the three MMX multiplication instructions. They are mostly for working with 16 bit integers. Each takes two parameters the first (destination) is an MMX register and the second can be an MMX register or a 64 bit memory location. PMULLW and PMULHW perform four multiplications between corresponding words SIMD style but the difference is in which part of the result you store in the destination (operand 1). PMULLW stores the four low 16 bits of the result and PMULHW stores the four top 16 bits. The final instruction is PMADDWD, packed multiply and add words to double-words. This is a Fused Multiply Add instruction (strictly speaking fused multiply adds are actually only for floating point). It multiplies four words with their corresponding words. Then it adds the low two answers together to form a double word and it does the same with the top two. The result in the destination is two double words.