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

[Milan Zamazal]

Laurent Pinchart <laurent.pinchart at ideasonboard.com> writes:

> On Thu, May 22, 2025 at 03:08:10PM +0200, Milan Zamazal wrote:
>> Hi Laurent,
>> 
>
>> thank you for the fix.
>> 
>> Laurent Pinchart <laurent.pinchart at ideasonboard.com> writes:
>> 
>> > 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.
>> 
>> Compiles fine in my environment.
>
> Can I get a Tested-by: tag ?

Tested-by: Milan Zamazal <mzamazal at redhat.com>

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