Documentation

Force Loop Unrolling by Using coder.unroll

The code generator uses heuristics to determine when to unroll a for-loop. To force loop unrolling, use coder.unroll. This affects only the for loop that is immediately after coder.unroll. For example:

function z = call_myloop()
%#codegen
z = myloop(5);
end

function b = myloop(n)
b = zeros(1,n);
coder.unroll();
for i = 1:n
    b(i)=i+n;
end
end

Here is the generated code for the for-loop:

  z[0] = 6.0;
  z[1] = 7.0;
  z[2] = 8.0;
  z[3] = 9.0;
  z[4] = 10.0;

To control when a for-loop is unrolled, use the coder.unroll flag argument. For example, unroll the loop only when the number of iterations is less than 10.

function z = call_myloop()
%#codegen
z = myloop(5);
end

function b = myloop(n)
unroll_flag = n < 10;
b = zeros(1,n);
coder.unroll(unroll_flag);
for i = 1:n
    b(i)=i+n;
end
end

To unroll a for-loop, the code generator must be able to determine the bounds of the for-loop. For example, code generation fails for the following code because the value of n is not known at code generation time.

function b = myloop(n)
b = zeros(1,n);
coder.unroll();
for i = 1:n
    b(i)=i+n;
end
end