A.5.218 PFNACC: Packed Single-Precision FP Negative Accumulate
PFNACC mm1,mm2/m64 ; 0F 0F /r 8A [PENT,3DNOW]
PFNACC performs a negative accumulate of the two single-precision FP
values in the source and destination registers. The result of the
accumulate from the destination register is stored in the low doubleword
of the destination, and the result of the source accumulate is stored in
the high doubleword of the destination register.
The operation is:
dst[0-31] := dst[0-31] - dst[32-63],
dst[32-63] := src[0-31] - src[32-63].