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color-lcms: cmsMAT3 is row-major after all

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Found out in https://github.com/mm2/Little-CMS/issues/483

This should be a complete no-op change, but there is one difference.
Previously matrix_inf_norm() summed over rows. Now it sums over columns
as it should be. This shouldn't hurt because it is only used to identify
identity matrices. The bug was actually in is_identity_matrix_stage()
because it deliberately passed what was assumed to be a transpose of the
matrix.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This commit is contained in:
Pekka Paalanen 2025-03-13 16:43:52 +02:00 • committed by Pekka Paalanen
parent f0ee8be804
commit fbf026653b
2 changed files with 8 additions and 13 deletions
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18
libweston/color-lcms/color-transform.c
View file

@ -192,7 +192,7 @@ matrix_inf_norm(const cmsMAT3 *mat)
double sum = 0.0;
for (col = 0; col < 3; col++)
sum += fabs(mat->v[col].n[row]);
sum += fabs(mat->v[row].n[col]);
if (infnorm < sum)
infnorm = sum;
@ -222,9 +222,9 @@ matrix_is_identity(const cmsMAT3 *mat, int bits_precision)
}
static const cmsMAT3 *
stage_matrix_transpose(const _cmsStageMatrixData *smd)
stage_matrix(const _cmsStageMatrixData *smd)
{
/* smd is row-major, cmsMAT3 is column-major */
/* Both are row-major. */
return (const cmsMAT3 *)smd->Double;
}
@ -259,7 +259,7 @@ is_identity_matrix_stage(const cmsStage *stage)
return false;
data = cmsStageData(stage);
return matrix_is_identity(stage_matrix_transpose(data),
return matrix_is_identity(stage_matrix(data),
MATRIX_PRECISION_BITS);
}
@ -274,15 +274,7 @@ multiply_matrix_stages(cmsContext context_id, cmsStage *next, cmsStage *prev)
prev_ = cmsStageData(prev);
next_ = cmsStageData(next);
/* res = prev^T * next^T */
_cmsMAT3per(&res, stage_matrix_transpose(next_),
stage_matrix_transpose(prev_));
/*
* res is column-major while Alloc function takes row-major;
* the cast effectively transposes the matrix.
* We return (prev^T * next^T)^T = next * prev.
*/
_cmsMAT3per(&res, stage_matrix(next_), stage_matrix(prev_));
ret = cmsStageAllocMatrix(context_id, 3, 3,
(const cmsFloat64Number*)&res, NULL);
abort_oom_if_null(ret);

3
tests/color_util.h
View file

@ -53,6 +53,9 @@ struct lcmsVEC3 {
float n[3];
};
/*
* While LittleCMS' cmsMAT3 is row-major, this here is colum-major.
*/
struct lcmsMAT3 {
/* array of columns */
struct lcmsVEC3 v[3];