def setheader(self, header):
        #(index 0)  9 bits: main part of primitive number   (#primitive)
        #(index 9)  8 bits: number of literals (#numLiterals)
        #(index 17) 1 bit:  whether a large frame size is needed (#frameSize)
        #(index 18) 6 bits: number of temporary variables (#numTemps)
        #(index 24) 4 bits: number of arguments to the method (#numArgs)
        #(index 28) 1 bit:  high-bit of primitive number (#primitive)
        #(index 29) 1 bit:  flag bit, ignored by the VM  (#flag)
        primitive, literalsize, islarge, tempsize, numargs, highbit = (
            splitter[9,8,1,6,4,1](header))
        primitive = primitive + (highbit << 10) ##XXX todo, check this
        self.literalsize = literalsize
        self.literals = [w_nil] * self.literalsize
        self.header = header
        self.argsize = numargs
        self.tempsize = tempsize
        self.primitive = primitive
        self.w_compiledin = None