A.5.219 PFPNACC: Packed Single-Precision FP Mixed Accumulate
PFPNACC mm1,mm2/m64 ; 0F 0F /r 8E [PENT,3DNOW]
PFPNACC performs a positive accumulate of the two single-precision
FP values in the source register and a negative accumulate of the
destination register. 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].