PSUBB           Subtraction with Wrap-around on Byte

PSUBB destination, source                            CPU: MMX

        Logic   mm(7..0)   <- mm(7..0)   - mm/m64(7..0)
                mm(15..8)  <- mm(15..8)  - mm/m64(15..8)
                mm(23..16) <- mm(23..16) - mm/m64(23..16)
                mm(31..24) <- mm(31..24) - mm/m64(31..24)
                mm(39..32) <- mm(39..32) - mm/m64(39..32)
                mm(47..40) <- mm(47..40) - mm/m64(47..40)
                mm(55..48) <- mm(55..48) - mm/m64(55..48)
                mm(63..56) <- mm(63..56) - mm/m64(63..56)

    PSUBB subtracts the bytes of the source operand from the bytes of
    the destination operand and returns the result to destination.
    When the result is too large or too small to be represented in a
    byte, the result wraps around and the lower 8 bits are written to
    the destination register.

    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 F8 /r    PSUBB mm, mm/m64