Floating-Point Multiplication to Handle a Net Slope Correction
This example shows how to use floating-point multiplication to handle a net slope correction. When converting floating-point data types to fixed-point data types in the generated code, a net slope correction is one method of scaling fixed-point data types. Scaling the fixed-point data types avoids overflow conditions and minimizes quantization errors.
For processors that support efficient multiplication, using floating-point multiplication to handle a net slope correction improves code efficiency. If the net slope correction has a value that is not a power of two, using division improves precision.
Note: This example requires a Fixed-Point Designer™ license.
Example
In the model rtwdemo_float_mul_for_net_slope_correction, a Convert block converts an input signal from a floating-point data type to a fixed-point data type. The net slope correction has a value of 3.
model = 'rtwdemo_float_mul_for_net_slope_correction';
open_system(model);
Generate Code
Create a temporary folder for the build and inspection process.
currentDir = pwd; [~,cgDir] = rtwdemodir();
Build the model.
rtwbuild(model)
### Starting build procedure for: rtwdemo_float_mul_for_net_slope_correction ### Successful completion of build procedure for: rtwdemo_float_mul_for_net_slope_correction Build Summary Top model targets built: Model Action Rebuild Reason =========================================================================================================================== rtwdemo_float_mul_for_net_slope_correction Code generated and compiled Code generation information file does not exist. 1 of 1 models built (0 models already up to date) Build duration: 0h 0m 23.795s
In these lines of rtwdemo_float_mul_for_net_slope_correction.c code, the code generator divides the input signal by 3.0F .
cfile = fullfile(cgDir,'rtwdemo_float_mul_for_net_slope_correction_ert_rtw',... 'rtwdemo_float_mul_for_net_slope_correction.c'); rtwdemodbtype(cfile,'/* Model step', '/* Model initialize', 1, 0);
/* Model step function */
void rtwdemo_float_mul_for_net_slope_correction_step(void)
{
/* Outport: '<Root>/Output' incorporates:
* DataTypeConversion: '<Root>/Data Type Conversion'
* Inport: '<Root>/Input'
*/
rtY.Output = (int16_T)(real32_T)floor((real_T)(rtU.Input / 3.0F));
}
Enable Optimization
Open the Configuration Parameters dialog box.
On the Math and Data Types pane, select Use floating-point multiplication to handle net slope corrections. This optimization is on by default.
Alternatively, you can use the command-line API to enable the optimization.
set_param(model, 'UseFloatMulNetSlope', 'on');
Generate Code with Optimization
rtwbuild(model)
### Starting build procedure for: rtwdemo_float_mul_for_net_slope_correction ### Successful completion of build procedure for: rtwdemo_float_mul_for_net_slope_correction Build Summary Top model targets built: Model Action Rebuild Reason ========================================================================================================== rtwdemo_float_mul_for_net_slope_correction Code generated and compiled Generated code was out of date. 1 of 1 models built (0 models already up to date) Build duration: 0h 0m 10.755s
In the optimized code, the code generator multiplies the input signal by the reciprocal of 3.0F , that is 0.333333343F .
rtwdemodbtype(cfile,'/* Model step', '/* Model initialize', 1, 0);
/* Model step function */
void rtwdemo_float_mul_for_net_slope_correction_step(void)
{
/* Outport: '<Root>/Output' incorporates:
* DataTypeConversion: '<Root>/Data Type Conversion'
* Inport: '<Root>/Input'
*/
rtY.Output = (int16_T)(real32_T)floor((real_T)(rtU.Input * 0.333333343F));
}
Close the model and the code generation report.
bdclose(model) rtwdemoclean; cd(currentDir)
See Also
Use floating-point multiplication to handle net slope corrections