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Instruction mmx - EMMS—Empty MMX State

Sets the values of all the tags in the FPU tag word to empty (all ones). This operation marks the MMX technology registers as available, so they can subsequently be used by floating-point instructions. (See Figure 7-11 in the Intel Architecture Software Developer’s Manual, Volume 1, for the format of the FPU tag word.) All other MMX instructions (other than the EMMS instruction) set all the tags in FPU tag word to valid (all zeros). The EMMS instruction must be used to clear the MMX technology state at the end of all MMX technology routines and before calling other procedures or subroutines that may execute floating-point instructions. If a floating-point instruction loads one of the registers in the FPU register stack before the FPU tag word has been reset by the EMMS instruction, a floating-point stack overflow can occur that will result in a floating-point exception or incorrect result.