[PATCH] libcamera: matrix: Fix compilation error in inverse() function

[Barnabás Pőcze]

Hi

2025. 05. 22. 14:42 keltezéssel, Laurent Pinchart írta:
> Some gcc versions report uninitialized variable usage:
> 
> In member function ‘constexpr T& libcamera::Span<T, 4294967295>::operator[](size_type) const [with T = unsigned int]’,
>      inlined from ‘void libcamera::matrixInvert(Span<const T>, Span<T, 4294967295>, unsigned int, Span<T, 4294967295>, Span<unsigned int>)::MatrixAccessor::swap(unsigned int, unsigned int) [with T = float]’ at ../../src/libcamera/matrix.cpp:194:13,
>      inlined from ‘bool libcamera::matrixInvert(Span<const T>, Span<T, 4294967295>, unsigned int, Span<T, 4294967295>, Span<unsigned int>) [with T = float]’ at ../../src/libcamera/matrix.cpp:255:14:
> ../../include/libcamera/base/span.h:362:76: error: ‘row’ may be used uninitialized [-Werror=maybe-uninitialized]
>    362 |         constexpr reference operator[](size_type idx) const { return data()[idx]; }
>        |                                                                      ~~~~~~^
> ../../src/libcamera/matrix.cpp: In function ‘bool libcamera::matrixInvert(Span<const T>, Span<T, 4294967295>, unsigned int, Span<T, 4294967295>, Span<unsigned int>) [with T = float]’:
> ../../src/libcamera/matrix.cpp:232:30: note: ‘row’ was declared here
>    232 |                 unsigned int row;
>        |                              ^~~
> 
> This is a false positive. Fix it by initializing the variable when
> declaring it.
> 
> Fixes: 6287ceff5aba ("libcamera: matrix: Add inverse() function")
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>   src/libcamera/matrix.cpp | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/matrix.cpp b/src/libcamera/matrix.cpp
> index ed22263b58f8..b7c07e896538 100644
> --- a/src/libcamera/matrix.cpp
> +++ b/src/libcamera/matrix.cpp
> @@ -229,7 +229,7 @@ bool matrixInvert(Span<const T> dataIn, Span<T> dataOut, unsigned int dim,
>   		 * Locate the next pivot. To improve numerical stability, use
>   		 * the row with the largest value in the pivot's column.
>   		 */
> -		unsigned int row;
> +		unsigned int row = pivot;

I am wondering if it could be set to `dim`, -1, etc. initially, and the below `if`
could be modified to check `row >= dim`, etc. That would avoid the value equality
check, which I think is a good thing.


Regards,
Barnabás Pőcze


>   		T maxValue{ 0 };
>   
>   		for (unsigned int i = pivot; i < dim; ++i) {
> 
> base-commit: efdbe3969841e342c30dfdced38b6ad9ad55dccf