Programming for MMX

Unfortunately, no compilers currently available have high-level language support for MMX. To use MMX, programmers must embed in-line assembly code into their C or C++ source code. It's the programmer's responsibility to manage the x86 registers shared by MMX and FP instructions. If the programmer doesn't clear the MMX registers (by using the Empty MMX State instruction) before executing an FP operation, the results could be disastrous. Even if compilers do eventually provide high-l evel support for MMX, it would have to be an awfully smart compiler to reschedule FP instructions that a programmer carelessly mixed into an MMX routine. It's unlikely that MMX and FP instructions would need to operate on the same register data; they use the registers in different ways. FP instructions see a push-pull stack of 80-bit FP values; MMX instructions see a random-access file of 64-bit integer values. However, x86 programmers are infamous for their crazy coding, so I suppose anything's possible. -- Tom R. Halfhill, senior editor