coder.loop.reverse

Reverse loop iteration order in generated code

Since R2023a

Syntax

coder.loop.reverse("loopID")

coder.loop.reverse

loopObj = coder.loop.reverse(___)

Description

coder.loop.reverse("loopID") prompts the code generator to reverse the loop iteration order for the for-loop whose index name is loopID in the generated code.

For more information about loop optimizations, see Optimize Loops in Generated Code.

coder.loop.reverse prompts the code generator to reverse the loop iteration order for the for loop defined immediately after this function call in the generated code. Use this transform when you know the upper bound of the loop iterator.

loopObj = coder.loop.reverse(___) returns a loop control object with transformSchedule property set to coder.loop.reverse. Use the apply method to apply the transform to the specified loop.

Examples

Reverse for-Loop Iteration Order in Generated Code

Use the coder.loop.reverse function to reverse the iteration order of for-loops in the generated code. Use the coder.loop.reverse function to optimize the generated code.

Define a MATLAB function applyReverseTransform that performs an addition operation on an array.

type applyReverseTransform.m

function out = applyReverseTransform
out = zeros(1,100);

coder.loop.reverse('i');
for i = 1:100
    out(i) = out(i) + i;
end

Generate code for this function at the command line.

codegen applyReverseTransform -config:lib

Warning: Code generation is using a coder.EmbeddedCodeConfig object. Because
Embedded Coder is not installed, this might cause some Embedded Coder features
to fail.

Code generation successful (with warnings): To view the report, open('codegen/lib/applyReverseTransform/html/report.mldatx')

Inspect the code generated for this function. The for-loop index in the generated function reduces from 99 to 0. This optimization can be beneficial if the upper-bound of the index is known.

type(fullfile("codegen","lib","applyReverseTransform","applyReverseTransform.c"))

/*
 * File: applyReverseTransform.c
 *
 * MATLAB Coder version            : 24.2
 * C/C++ source code generated on  : 05-Sep-2024 16:34:53
 */

/* Include Files */
#include "applyReverseTransform.h"
#include <string.h>

/* Function Definitions */
/*
 * Arguments    : double out[100]
 * Return Type  : void
 */
void applyReverseTransform(double out[100])
{
  int i;
  memset(&out[0], 0, 100U * sizeof(double));
  for (i = 99; i >= 0; i--) {
    out[i] += (double)i + 1.0;
  }
}

/*
 * File trailer for applyReverseTransform.c
 *
 * [EOF]
 */

Input Arguments

loopID — for-loop index name

string scalar | character vector

for-loop identifier or index name to reverse, specified as a character vector a string scalar.

Data Types: char | string

Output Arguments

loopObj — Loop control object

coder.loop.Control object

Loop control object with transformSchedule property set to coder.loop.reverse.

Version History

Introduced in R2023a