Lookup Table Function Code Replacement

You can configure the algorithm for table lookup operations and index searches and generate code. If the code generated for available algorithm options does not meet requirements for your application, create custom code replacement table entries to replace the generated algorithm code. You can develop a code replacement library to optimize the performance of algorithms in a lookup table block. For more information, see Develop a Code Replacement Library. For more information about using lookup table blocks, see Nonlinearity.

Lookup Table Function Signatures

To create code replacement table entries for a function corresponding to a lookup table algorithm, you must have:

• Information about the conceptual function signature.

• Relevant algorithm parameters.

This table provides the conceptual function signature information.

Conceptual Function SignatureArgument Summary
`y1 = interp1D(u1, u2, u3, u4)``y1` – output
`u1` – index
`u2` – fraction
`u3` – table data
`u4` – table dimension length
`y1 = interp2D(u1, u2, u3, u4, u5, u6, u7)``y1` – output
`u1, u3` – index
`u2, u4` – fraction
`u5` – table data
`u6, u7` – table dimension lengths
```y1 = interp3D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10)````y1` – output
`u1, u3, u5` – index
`u2, u4, u6` – fraction
`u7` – table data
`u8, u9, u10` – table dimension lengths
```y1 = interp4D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10, u11, u12, u13)````y1` – output
```u1, u3, u5, u7``` – index
`u2, u4, u6, u8` – fraction
`u9` – table data
`u10, u11, u12, u13` – table dimension lengths
```y1 = interp5D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10, u11, u12, u13, u14, u15, u16)````y1` – output
```u1, u3, u5, u7, u9``` – index
`u2, u4, u6, u8, u10` – fraction
`u11` – table data
`u12, u13, u14, u15, u16` – table dimension lengths
```y1 = interpND({ui, uf,}... ut, un...)````y1` – output
`ui`, `uf` is an index and fraction pair per dimension
`ut` – table data
`un` – table dimension lengths

Explicit values
```y1 = lookup1D(u1, u2, u3, u4)```

`y1` – output
`u1` – input
`u2` – breakpoint data
`u3` – table data
`u4` – table dimension length

Even spacing
```y1 = lookup1D(u1, u2, u3, u4, u5)```

`y1` – output
`u1` – input
`u2` – first point of breakpoint data
`u3` – spacing of breakpoints
`u4` – table data
`u5` – table dimension length

Explicit values
```y1 = lookup2D(u1, u2, u3, u4, u5, u6, u7)```

`y1` – output
`u1, u2` – input
`u3, u4` – breakpoint data
`u5` – table data
`u6, u7` – table dimension lengths

Even spacing
```y1 = lookup2D(u1, u2, u3, u4, u5, u6, u7, u8, u9)```

`y1` – output
`u1, u2` – input
`u3, u5` – first point of breakpoint data
`u4, u6` – spacing of breakpoints
`u7` – table data
`u8, u9` – table dimension lengths

Explicit spacing
```y1 = lookup3D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10)```

`y1` – output
`u1, u2, u3` – input
`u4, u5, u6` – breakpoint data
`u7` – table data
`u8, u9, u10` – table dimension lengths

Even spacing
```y1 = lookup3D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10, u11, u12, u13)```

`y1` – output
`u1, u2, u3` – input
`u4, u6, u8` – first point of breakpoint data
`u5, u7, u9` – spacing of breakpoints
`u10` – table data
`u11, u12, u13` – table dimension lengths

Explicit values
```y1 = lookup4D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10, u11, u12, u13)```

`y1` – output
```u1, u2, u3, u4``` – input
`u5, u6, u7, u8` – breakpoint data
`u9` – table data
`u10, u11, u12, u13` – table dimension lengths

Even spacing
```y1 = lookup4D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10, u11, u12, u13, u14, u15, u16, u17)```

`y1` – output
```u1, u2, u3, u4``` – input
`u5, u7, u9, u11` – first point of breakpoint data
`u6, u8, u10, u12` – spacing of breakpoints
`u13` – table data
`u14, u15, u16, u17` – table dimension lengths

Explicit values
```y1 = lookup5D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10, u11, u12, u13, u14, u15, u16)```

`y1` – output
```u1, u2, u3, u4, u5``` – input
`u6, u7, u8, u9, u10` – breakpoint data
`u11` – table data
`u12, u13, u14, u15, u16` – table dimension lengths

Even spacing
```y1 = lookup5D(u1, u2, u3, u4, u5, u6, u7, u8, u9, u10, u11, u12, u13, u14, u15, u16, u17, u18, u19, u20, u21)```

`y1` – output
```u1, u2, u3, u4, u5``` – input
`u6, u8, u10, u12, u14` – first point of breakpoint data
```u7, u9, u11, u13, u15``` – spacing of breakpoints
`u16` – table data
`u17, u18, u19, u20, u21` – table dimension lengths

Explicit values
```y1 = lookupND(un,..., ub,..., ut, un...)```

`y1` – output
`un`, input per dimension
`ub`, breakpoint per dimension
`ut` – table data
`un` – table dimension lengths

Even spacing
```y1 = lookupND(un,..., {ufn, usn,}... ut, un...)```

`y1` – output
`un` – input per dimension
`ufn` – first point of breakpoint data per dimension
`usn` – spacing of breakpoint per dimension
`ut` – table data
`un` – table dimension lengths
`y1 = lookupND_Direct(u1, u2,...ui, ui+1)``y1` – output
`u1...ui` – input
`ui+1` – table data

Explicit values
```y1, y2 = prelookup(u1, u2, u3)```

`y1` – index
`y2` – fraction
`u1` – input
`u2` – breakpoint data
`u3` – number of breakpoints

Evenly spaced
```y1, y2 = prelookup(u1, u2, u3, u4)```

`y1` – index
`y2` – fraction
`u1` – input
`u2` – first point of breakpoint data
`u3` – spacing of breakpoints
`u4` – number of breakpoints

For the table and breakpoint data, the conceptual function uses matrix arguments by default. If the lookup table object has the parameter Allow multiple instances of this type to have different table and breakpoint sizes enabled, the conceptual function uses pointer arguments for the table and breakpoint data. To replace a lookup table function that uses pointer arguments, you must create the entry programmatically.

When defining a table entry programmatically, you might also need to change the values of required (primary) and optional algorithm parameters.

• Set values for required parameters to achieve code replacement.

• If you do not set a value for an optional parameter, the algorithm parameter software applies `don't care`. The code replacement software ignores the parameter while searching for matches.

Interactively Develop a Code Replacement Library

This example shows how to specify a code replacement table entry for a lookup table algorithm `interp1D` by using the Code Replacement Tool.

1. Open the Code Replacement Tool (crtool), from the MATLAB command line with the following command:

`>>crtool`
2. Create a table.

1. From the crtool context menu, select File > New Table.

2. In the right pane, name the table `crl_LUT`. Click Apply.

3. Create an entry. From the crtool context menu, select File > New entry > Function.

4. Create entry parameters. In the Function drop-down list, select `custom`. Function information appears in the crtool. For this example, specify the parameter as `lookup1D`. Set these algorithm parameters as shown in the crtool snapshot below:

• Extrapolation method — Linear

• Interpolation method — Linear point-slope

• Integer rounding mode — Round

• Saturate on overflow — off

• Index search method — Linear search

• Remove out-of-range input protection — off

• Support tunable table size — off

• Use last table value for inputs at or above last breakpoint — off

• Begin index search using previous index result — off

• Use algorithms optimized for row-major array layout — off

5. Create the conceptual representation. The conceptual representation describes the signature of the function that you want to replace. In the Conceptual function subsection of the crtool, specify the return argument, `y1`, and the input argument `u1` with the Data Type of `double` and `u4` , with the Data Type of `uint32` and the Argument Type of `Scalar`.

Specify the Argument Type of input arguments `u2` and `u3` as `Matrix` and Data Type as `double`. Set the Algorithm parameters as shown in the figure below.

6. Create the implementation representation. The implementation representation describes the signature of the optimization function. For this example, to specify that the implementation arguments have the same order and properties as the conceptual arguments, select the Make conceptual and implementation argument types the same check box.

Add the return argument `y1` and the arguments ```u1, u2, u3``` and `u4`.

Specify a Name for the replacement function under Function prototype.

7. Specify build information. Click the Build Information tab to open the build requirements pane. Specify the files (source, header, object) that the code generator requires for code replacement. For this example, you do not need to specify build information.

8. Validate and save the table. Click the Mapping Information tab and verify the fields are filled in as shown. Click Validate entry. In the crtool context menu, select File > Save table > Save.

9. Register a code replacement library. Registration creates a library composed of the tables that you specify. Select File > Generate registration file. In the Generate registration file dialog box, fill out these fields:

To use your code replacement library, refresh your current MATLAB session with the command:

`>>sl_refresh_customizations`

10. Verify the code replacement library. From the MATLAB command line, open the library by using the Code Replacement Viewer and verify that the table and entry are correctly specified. For more information, see Verify Code Replacement Library. Configure your model to use the code replacement library, generate code, and verify that replacement occurs as expected. If unexpected behavior occurs, examine the hit and miss logs to troubleshoot the issues.

Programmatically develop a code replacement library

1. Open the programmatic interface from the MATLAB menu by selecting New > Function.

2. Create a table.

1. Create a function with the name of your code replacement library table that does not have arguments and returns a table object. You can use this function to call your code replacement library table.

2. Create a table object by calling `RTW.TflTable`.

```function hTable = my_lookup_replacement_table % Create a function to call the code replacement library table %% Create a table object hTable = RTW.TflTable; ```
3. Create an entry. Because this example replaces a function, create a code replacement entry in your table by calling the entry function `RTW.TflCFunctionEntry`.

```function hTable = my_lookup_replacement_table % Create a code replacement library table %% Create a table object hTable = RTW.TflTable; %% Create an entry hEntry = RTW.TflCFunctionEntry; ```
4. Create entry parameters. Because this examples replaces a function, create entry parameters by calling the function `setTflCFunctionEntryParameters`.

```function hTable = my_lookup_replacement_table() % Create a code replacement library table %% Create a table object hTable = RTW.TflTable; %% Create an entry hEntry = RTW.TflCFunctionEntry; %% Create entry parameters setTflCFunctionEntryParameters(hEntry, ... 'Key', 'lookup1D', ... 'Priority', 100, ... 'ImplementationName', 'my_Lookup1D_Repl', ... 'ImplementationHeaderFile', 'myLookup1D.h', ... 'ImplementationSourceFile', 'myLookup1D.c', ... 'GenCallback', 'RTW.copyFileToBuildDir');```
5. Create the conceptual representation. The conceptual representation describes the signature of the function that you want to replace. To explicitly specify argument properties, call the function `getTflArgFromString`.

```function hTable = my_lookup_replacement_table() % Create a code replacement library table %% Create a table object hTable = RTW.TflTable; %% Create an entry hEntry = RTW.TflCFunctionEntry; %% Create entry parameters setTflCFunctionEntryParameters(hEntry, ... 'Key', 'lookup1D', ... 'Priority', 100, ... 'ImplementationName', 'my_Lookup1D_Repl', ... 'ImplementationHeaderFile', 'myLookup1D.h', ... 'ImplementationSourceFile', 'myLookup1D.c', ... 'GenCallback', 'RTW.copyFileToBuildDir'); %% Create the conceptual representation arg = hEntry.getTflArgFromString('y1','double'); arg.IOType = 'RTW_IO_OUTPUT'; addConceptualArg(hEntry, arg); arg = hEntry.getTflArgFromString('u1','double'); addConceptualArg(hEntry, arg); arg = RTW.TflArgMatrix('u2', 'RTW_IO_INPUT', 'double'); arg.DimRange = [0 0; Inf Inf]; addConceptualArg(hEntry, arg); arg = RTW.TflArgMatrix('u3', 'RTW_IO_INPUT', 'double'); arg.DimRange = [0 0; Inf Inf]; addConceptualArg(hEntry, arg); arg = hEntry.getTflArgFromString('u4','uint32'); addConceptualArg(hEntry, arg); ```
6. Create the implementation representation. The implementation representation describes the signature of the optimization function. To specify that the implementation arguments have the same order and properties as the conceptual arguments, call the function `getTflArgFromString`.

```function hTable = my_lookup_replacement_table() % Create a code replacement library table %% Create a table object hTable = RTW.TflTable; %% Create an entry hEntry = RTW.TflCFunctionEntry; %% Create entry parameters setTflCFunctionEntryParameters(hEntry, ... 'Key', 'lookup1D', ... 'Priority', 100, ... 'ImplementationName', 'my_Lookup1D_Repl', ... 'ImplementationHeaderFile', 'myLookup1D.h', ... 'ImplementationSourceFile', 'myLookup1D.c', ... 'GenCallback', 'RTW.copyFileToBuildDir'); %% Create the conceptual representation arg = hEntry.getTflArgFromString('y1','double'); arg.IOType = 'RTW_IO_OUTPUT'; addConceptualArg(hEntry, arg); arg = hEntry.getTflArgFromString('u1','double'); addConceptualArg(hEntry, arg); arg = RTW.TflArgMatrix('u2', 'RTW_IO_INPUT', 'double'); arg.DimRange = [0 0; Inf Inf]; addConceptualArg(hEntry, arg); arg = RTW.TflArgMatrix('u3', 'RTW_IO_INPUT', 'double'); arg.DimRange = [0 0; Inf Inf]; addConceptualArg(hEntry, arg); arg = hEntry.getTflArgFromString('u4','uint32'); addConceptualArg(hEntry, arg); algParams = getAlgorithmParameters(hEntry); algParams.InterpMethod = 'Linear'; algParams.ExtrapMethod = 'Clip'; algParams.UseRowMajorAlgorithm = 'off'; algParams.RndMeth = 'Round'; algParams.IndexSearchMethod = 'Linear search'; algParams.UseLastTableValue = 'off'; algParams.RemoveProtectionInput = 'off'; algParams.SaturateOnIntegerOverflow = 'off'; algParams.SupportTunableTableSize = 'off'; algParams.BPPower2Spacing = 'off'; algParams.BeginIndexSearchUsingPreviousIndexResult = 'off'; setAlgorithmParameters(hEntry, algParams); %% Create the Implementation Representation arg = hEntry.getTflArgFromString('y1','double'); arg.IOType = 'RTW_IO_OUTPUT'; hEntry.Implementation.setReturn(arg); arg = hEntry.getTflArgFromString('u1','double'); hEntry.Implementation.addArgument(arg); arg = hEntry.getTflArgFromString('u2','double*'); hEntry.Implementation.addArgument(arg); arg = hEntry.getTflArgFromString('u3','double*'); hEntry.Implementation.addArgument(arg); arg = hEntry.getTflArgFromString('u4','uint32'); hEntry.Implementation.addArgument(arg); %% Add the entry to the table hTable.addEntry(hEntry); ```
7. Specify build information. In the entry parameters, specify files (header, source, object) that the code generator needs for code replacement. For this example, build information is not required.

8. Validate and save the customization file. From the MATLAB menu, save this customization file by selecting File > Save. From the command line, validate the code replacement library table by calling it:

`>> hTable = my_lookup_replacement_table`
9. Register the code replacement library. Registration creates a code replacement library by defining the library name, code replacement tables, and other information. Create a registration file (a new function file) with these specifications:

```function rtwTargetInfo(cm) cm.registerTargetInfo(@loc_register_crl); end function this = loc_register_crl this(1) = RTW.TflRegistry; this(1).Name = 'CRL for LUT 1D function replacement’; this(1).TableList = {'my_lookup_replacement_table.m'}; % table created in this example this(1).TargetHWDeviceType = {'*'}; this(1).Description = 'Example code replacement library'; end ```

To use your code replacement library, refresh your current MATLAB session with the command:

`>>sl_refresh_customizations`

10. Verify the code replacement library. From the MATLAB command line, open the library by using the Code Replacement Viewer and verify that the table and entry are correctly specified. For more information, see Verify Code Replacement Library. Configure your model to use the code replacement library, generate code, and verify that replacement occurs as expected. If unexpected behavior occurs, examine the hit and miss logs to troubleshoot the issues.

Generate Code by Using Lookup Table Code Replacement Library

In this section, you generate code using the code replacement library that you created in the first two sections of this example. A Lookup table function is replaced with a call to a custom function in the generated code. This example does not provide an implementation function. Write your own implementation.

Example Model

Open the model `crl_LUTfunction` for configuring the code replacement library.

```open_system('crl_LUTfunction'); copyfile LutFnRtwTargetInfo.txt rtwTargetInfo.m ```

Run the MATLAB customization file to create a code replacement table and register the file. The customization file has already been executed. Run the sl_refresh_customizations function to load the library.

```sl_refresh_customizations; ```

Enable Code Replacement Library

1. Open the Configuration Parameters dialog box.

2. On the Interface pane, set Code Replacement Library by clicking Select and adding `CRL for LUT function replacement` to the Selected code replacement libraries - prioritized list pane.

```% % Alternatively, use the command-line API to enable the code replacement: set_param('crl_LUTfunction', 'CodeReplacementLibrary', 'CRL for LUT function replacement'); ```

Generate code from the model:

```evalc('slbuild(bdroot)'); ```

View the generated code. Here is a portion of `crl_LUTfunction.c`.

```cfile = fullfile('crl_LUTfunction_ert_rtw','crl_LUTfunction.c'); coder.example.extractLines(cfile,'/* Model step function ','/* Model initialize function',1, 1); ```
```/* Model step function */ void crl_LUTfunction_step(void) { int32_T iU; /* Lookup_n-D: '<Root>/1-D Lookup Table2' incorporates: * Constant: '<Root>/Constant2' */ for (iU = 0; iU < 9; iU++) { crl_LUTfunction_Y.Y1[iU] = my_Lookup1D_Repl (crl_LUTfunction_ConstP.Constant2_Value[iU], &crl_LUTfunction_ConstP.uDLookupTable2_bp01Data[0], &crl_LUTfunction_ConstP.uDLookupTable2_tableData[0], 10U); } /* End of Lookup_n-D: '<Root>/1-D Lookup Table2' */ } ```

The Lookup Table function is replaced with a custom `my_Lookup1D_Repl` function.

Close the model and code generation report.

```delete ./rtwTargetInfo.m bdclose('crl_LUTfunction'); ```