MATLAB .p file is a content-obscured version of .m source file¹, and it is commonly used in some scenarios where technicians only want to share some functions they have realized using MATLAB with other people, rather than the whole source code. This usually occurs during the procession of cooperation between different companies or organizations as some technologies are patented and protected by intellectual property.

The conversion of .p file from .m source file is very easy to perform using MATLAB pcode function², and the performance of both files is equivalent¹.

An official example shows how to use pcode function to generate .p code corresponding to the original .m file²:

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% myfunc.m file
function y = myfunc(x)
y = sqrt(x.^3 + x.^2 + x + 1);
end

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% Command line
pcode myfunc -R2022a

Using parameter -R2020a is to choose a more complex obfuscation algorithm than default setting -R2007b.

After executing the command, the myfunc.p file will occur in the current folder. The myfunc.p file is not permitted to be inspected, edited, or converted to C code. For example, if we execute³:

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codegen myfunc -config:lib -args {3.14}

MATLAB will throw an error while generating:

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??? P-file '...\myfunc.p' is not authorized for compilation. To support compilation,
please consider using 'coder.allowpcode('plain')' in this file.

Error in ==> myfunc Line: 1 Column: 1
Code generation failed: View Error Report

Error using codegen

But, the error information implies a solution that we could add the code coder.allowpcode('plain') in the myfunc.m file⁴:

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function y = myfunc(x)  %#codegen
coder.allowpcode('plain')
y = sqrt(x.^3 + x.^2 + x + 1);
end

At this time, we could re-convert this function to .p file and try to generate C language code again; it will generate successfully.

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>> codegen myfunc -config:lib -args {3.14}
Code generation successful.

We could open ...\codegen\lib\myfunc\myfunc.c to inspect the results:

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/* ... */
static double rt_powd_snf(double u0, double u1)
{
  double y;
  if (rtIsNaN(u0) || rtIsNaN(u1)) {
    y = rtNaN;
  } else {
    double d;
    double d1;
    d = fabs(u0);
    d1 = fabs(u1);
    if (rtIsInf(u1)) {
      if (d == 1.0) {
        y = 1.0;
      } else if (d > 1.0) {
        if (u1 > 0.0) {
          y = rtInf;
        } else {
          y = 0.0;
        }
      } else if (u1 > 0.0) {
        y = 0.0;
      } else {
        y = rtInf;
      }
    } else if (d1 == 0.0) {
      y = 1.0;
    } else if (d1 == 1.0) {
      if (u1 > 0.0) {
        y = u0;
      } else {
        y = 1.0 / u0;
      }
    } else if (u1 == 2.0) {
      y = u0 * u0;
    } else if ((u1 == 0.5) && (u0 >= 0.0)) {
      y = sqrt(u0);
    } else if ((u0 < 0.0) && (u1 > floor(u1))) {
      y = rtNaN;
    } else {
      y = pow(u0, u1);
    }
  }
  return y;
}

/*
 * Arguments    : double x
 * Return Type  : double
 */

double myfunc(double x)
{
  return sqrt(((rt_powd_snf(x, 3.0) + x * x) + x) + 1.0);
}
/* ... */

References