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Is there a version switch for codegen?

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Is it possible to branch which part of the code is generated to C based on the current Matlab version, that is generating code at compile time?
For example I have a function which uses runtime recursion (which is only possible after R2016B) and an alternative without runtime recursion and I want to somehow switch between the factorial and the recursive line in the below simplified example based on the Matlab version generaing code from this function in order to make it backwards compatible with Matlab before R2016B.
function [x] = codertest(a)
if verLessThan('matlab', '9.1')% starting with R2016B runtime recursion is allowed in code generation
% some pragma like %#codegen or a function like coder.target is needed here to switch at compile time
x = factorial(a);
else
x = recursive(a);
end
end
function [rec] = recursive(x)
if x == 1
rec = x;
else
rec = x*recursive(x - 1);
end
end
The file can be compiled with:
>> Tx = coder.typeof(1, [1, 1], [false, false]);
>> codegen('codertest.m', '-args', '{Tx}');
When I run these lines, Matlab before R2016B should therefore generate code using the "factorial" lines and Matlab after R2016B should use the "recursive" lines.
Simply using
coder.extrinsic('verLessThan');
does not solve the problem because this switches at runtime and then code generation will fail e.g. in R2015B with
??? Recursive calls are not allowed. Function 'recursive' participated in a recursive call.
which is exactly what I try to prevent.

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Accepted Answer

Ryan Livingston
Ryan Livingston on 2 Nov 2019
Edited: Ryan Livingston on 2 Nov 2019
Use coder.const to forcibly constant fold the extrinsic call to verLessThan
if coder.const(verLessThan('matlab', '9.1'))
% Older style code
else
% Newer style code
end
The doc on this has more examples on constant folded extrinsic functions:

  2 Comments

Walter Roberson
Walter Roberson on 3 Nov 2019
Ah, I had not encountered that before!
Patrick Vogt
Patrick Vogt on 3 Nov 2019
Works perfectly, thank you.

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