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Determine Output Type Using the Input Type

The following sample code from lines 242 through 260 of sfun_user_fxp_asr.c gives an example of using the data type of the input to your S-function to calculate the output data type. Notice that in this code

  • The output is signed or unsigned to match the input (a).

  • The output is the same word length as the input (b).

  • The fraction length of the output depends on the input fraction length and the number of shifts (c).

    #define MDL_SET_INPUT_PORT_DATA_TYPE
static void mdlSetInputPortDataType(SimStruct *S, int port,
					DTypeId dataTypeIdInput)
{
    if ( isDataTypeSupported( S, dataTypeIdInput ) )
    {
        DTypeId dataTypeIdOutput;

        ssSetInputPortDataType( S, port, dataTypeIdInput );

        dataTypeIdOutput = ssRegisterDataTypeFxpBinaryPoint(
					S,
			ssGetDataTypeFxpIsSigned( S, dataTypeIdInput ), (a)
			ssGetDataTypeFxpWordLength( S, dataTypeIdInput ), (b)
			ssGetDataTypeFractionLength( S, dataTypeIdInput )
					- V_NUM_BITS_TO_SHIFT_RGHT, (c)
            0 /* false means do NOT obey data type override
					           setting for this subsystem */ );

        ssSetOutputPortDataType( S, 0, dataTypeIdOutput );
    }
}