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coder.ignoreConst

Prevent use of constant value of expression for function specializations

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Syntax

coder.ignoreConst(expression)

Description

coder.ignoreConst(expression) prevents the code generator from using the constant value of expression to create function specializations. coder.ignoreConst(expression) returns the value of expression.

example

Examples

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Use coder.ignoreConst to prevent function specializations for a function that is called with constant values.

Write the function call_myfn, which calls myfcn.

function [x, y] = call_myfcn(n)
%#codegen
x = myfcn(n, 'mode1');
y = myfcn(n, 'mode2');
end

function y = myfcn(n,mode)
coder.inline('never');
if strcmp(mode,'mode1')
    y = n;
else
    y = -n;
end
end

Generate standalone C code. For example, generate a static library. Enable the code generation report.

codegen -config:lib call_myfcn -args {1} -report

In the code generation report, you see two function specializations for call_myfcn.

This image shows the function call_myfcn and the function specializations in the code generation report.

The code generator creates call_myfcn>myfcn>1 for mode with a value of 'mode1'. It creates call_myfcn>myfcn>2 for mode with a value of 'mode2'.

In the generated C code, you see the specializations my_fcn and b_my_fcn.

static double b_myfcn(double n)
{
  return -n;
}

static double myfcn(double n)
{
  return n;
}

To prevent the function specializations, instruct the code generator to ignore that values of the mode argument are constant.

function [x, y] = call_myfcn(n)
%#codegen
x = myfcn(n, coder.ignoreConst('mode1'));
y = myfcn(n, coder.ignoreConst('mode2'));
end

function y = myfcn(n,mode)
coder.inline('never');
if strcmp(mode,'mode1')
    y = n;
else
    y = -n;
end
end

Generate the C code.

codegen -config:lib call_myfcn -args {1} -report

In the code generation report, you do not see multiple function specializations.

This image shows the function call_myfcn after instructing the code generator to ignore that the values of the mode argument are constant in the code generation report.

In the generated C code, you see one function for my_fcn.

Input Arguments

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Expression whose value is to be treated as a nonconstant, specified as a MATLAB expression.

More About

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Function Specialization

Version of a function in which an input type, size, complexity, or value is customized for a particular invocation of the function.

Function specialization produces efficient C code at the expense of code duplication. The code generation report shows all MATLAB function specializations that the code generator creates. However, the specializations might not appear in the generated C/C++ code due to later transformations or optimizations.

Tips

  • For some recursive function calls, you can use coder.ignoreConst to force run-time recursion. See Force Code Generator to Use Run-Time Recursion.

  • coder.ignoreConst(expression) prevents the code generator from using the constant value of expression to create function specializations. It does not prevent other uses of the constant value during code generation.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Version History

Introduced in R2017a

See Also

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