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MMX is not really dead - how else would you do byte level integer processing? AFAIK the later SIMD instructions are all float based

Not true, SSE2 added support for performing all the MMX operations, but at 128-bit width in the SSE registers. AVX2 expanded that out to 256-bit width later.

Right--there is no reason to use MMX today, and two good reasons not to. SSE2 and follow-on extensions give better performance, and the SSE registers do not alias the x87 stack, which removes the risk of a particularly nasty and difficult to diagnose class of bug (failure to issue EMMS following MMX usage can cause x87 stack corruption billions of cycles later in an apparently unrelated call tree).


as i told you guys above, i didn't have sse2+ around at the time i wrote those chapters.

thanks a million for the note on x87 stack corruption, i didn't know about that bug. ;)

hack on,


SSE2 introduced integer instructions.

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