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PCMPGTB         Packed Compare for Greater Than, Byte

PCMPGTB destination, source                          CPU: MMX

        Logic   if mm(7..0)   > mm/m64(7..0)
                     mm(7..0)   <- 0FFh
                else mm(7..0)   <- 0
                endif
                if mm(15..8)  > mm/m64(15..8)
                     mm(15..8)  <- 0FFh
                else mm(15..8)  <- 0
                endif
                if mm(23..16) > mm/m64(23..16)
                     mm(23..16) <- 0FFh
                else mm(23..16) <- 0
                endif
                if mm(31..24) > mm/m64(31..24)
                     mm(31..24) <- 0FFh
                else mm(31..24) <- 0
                endif
                if mm(39..32) > mm/m64(39..32)
                     mm(39..32) <- 0FFh
                else mm(39..32) <- 0
                endif
                if mm(47..40) > mm/m64(47..40)
                     mm(47..40) <- 0FFh
                else mm(47..40) <- 0
                endif
                if mm(55..48) > mm/m64(55..48)
                     mm(55..48) <- 0FFh
                else mm(55..48) <- 0
                endif
                if mm(63..56) > mm/m64(63..56)
                     mm(63..56) <- 0FFh
                else mm(63..56) <- 0
                endif
    
    PCMPGTB compares the signed bytes in the destination operand to the
    signed bytes in the source operand. If the signed data elements in
    destination are greater than those in the source operand, the
    corresponding data element in the destination operand is set to all
    ones. Otherwise, it is set to all zeros. 

    The destination operand is an MMX register. The source operand can
    either be an MMX register or a 64-bit memory operand.


    Opcode      Format
    0F 64 /r    PCMPGTB mm, mm/m64