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Remove Code That Maps NaN to Integer Zero

This example shows how to remove code that maps NaN to integer zero. For floating-point to integer conversions involving saturation, Simulink converts NaN to integer zero during simulation. If your model contains an input value of NaN, you can specify that the code generator produce code that maps NaN to zero. Without this code, there is a mismatch between simulation and code generation results because in Standard C, every condition involving NaN evaluates to false.

If input values of NaN doe not exist in your application, you can remove code that maps NaN to integer zero. Removing this code reduces the size and increases the speed of the generated code.

Example Model

In this model, a Data Type Conversion block converts an input signal from a double to a uint8. In this example, the model is named conversion_ex.

  1. Use Inport, Outport, and Data Type Conversion blocks to create the example model.

  2. Open the Inport Block Parameters dialog box and click the Signal Attributes tab. For the Data Type parameter, select double.

  3. Open the Data Type Conversion dialog box. For the Output data type parameter, select uint8.

  4. Select Saturate on integer overflow. Selecting this parameter specifies that an out-of-range signal value equals either the minimum or maximum value that the data type can represent.

  5. For the signal feeding into the Data Type Conversion block, open the Signal Properties dialog box. Enter a name of U. In the Code Mappings editor, under Signals, set the storage Class, to ImportedExtern.

  6. For the signal leaving the Data Type Conversion block, open the Signal Properties dialog box. Enter a name of Y. In the Code Mappings editor, under Signals, set the storage class, to ImportedExtern.

Generate Code

  1. Set the Configuration Parameters > Solver > Solver options > Type parameter to Fixed-step.

  2. Disable the Configuration Parameters > Optimization > Advanced parameters > Remove code from floating-point to integer conversions with saturation that maps NaN to zero parameter.

  3. Enable the Configuration Parameters > Code Generation > Report > Create code generation report parameter and the Open report automatically parameter.

  4. Enable the Configuration Parameters > Code Generation > Build process > Generate code only parameter. Then, in the model window, press Ctrl+B. When code generation is complete, an HTML code generation report opens.

  5. In the Code Generation report, select the nan_int_ex.c file and view the model step function. For an input value of NaN, there is agreement between the generated code and simulation because NaN maps to integer zero.

/* Model step function */
void nan_int_ex_step(void)
{
  /* DataTypeConversion: '<Root>/Data Type Conversion' incorporates:
   *  Inport: '<Root>/In1'
   */
  if (U < 256.0) {
    if (U >= 0.0) {
      Y = (uint8_T)U;
    } else {
      Y = 0U;
    }
  } else if (U >= 256.0) {
    Y = MAX_uint8_T;
  } else {
    Y = 0U;
  }

Generate Code with Optimization

  1. Enable the Configuration Parameters > Optimization > Code generation > Integer and fixed-point > Remove code from floating-point to integer conversions that wraps out-of-range values parameter. Generate code.

  2. In the Code Generation report, select the nan_int_ex.c section and view the model step function. The generated code maps NaN to 255 and not integer zero. The generated code is more efficient without the extra code that maps NaN to integer zero, but the execution of the generated code does not produce the same results as simulation for NaN values.

/* Model step function */
void nan_int_ex_step(void)
{
  /* DataTypeConversion: '<Root>/Data Type Conversion' incorporates:
   *  Inport: '<Root>/In1'
   */
  if (U < 256.0) {
    if (U >= 0.0) {
      Y = (uint8_T)U;
    } else {
      Y = 0U;
    }
  } else {
    Y = MAX_uint8_T;
  }
 
  /* End of DataTypeConversion: '<Root>/Data Type Conversion' */

See Also

Related Topics