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PSUBUSB         Subtract Unsigned with Saturation on Byte

PSUBUSB destination, source                          CPU: MMX

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

    PSUBUSB subtracts the bytes of the source operand from the bytes of
    the destination operand and writes the results to the destination
    register.
    If the result element is less than zero (a negative value), it is
    saturated to 00h.

    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 D8 /r    PSUBUSB mm, mm/m64