9.16.10 Intels MMX and AMDs 3DNow! SIMD Operations

as supports Intels MMX instruction set (SIMD instructions for integer data), available on Intels Pentium MMX processors and Pentium II processors, AMDs K6 and K6-2 processors, Cyrix M2 processor, and probably others. It also supports AMDs 3DNow! instruction set (SIMD instructions for 32-bit floating point data) available on AMDs K6-2 processor and possibly others in the future.

Currently, as does not support Intels floating point SIMD, Katmai (KNI).

The eight 64-bit MMX operands, also used by 3DNow!, are called %mm0, %mm1, ... %mm7. They contain eight 8-bit integers, four 16-bit integers, two 32-bit integers, one 64-bit integer, or two 32-bit floating point values. The MMX registers cannot be used at the same time as the floating point stack.

See Intel and AMD documentation, keeping in mind that the operand order in instructions is reversed from the Intel syntax.