BLI_math: improve symmetrical values from sin_cos_from_fraction

When plotting equally distant points around a circle support an extra
axis of symmetry so twice as many exact values are repeated than
originally added in [0], see code-comments for a detailed explanation.
Tests to ensure accuracy and exact symmetry have been added too.

Follow up on fix for T87779.

[0]: 087f27a52f7857887e90754d87a7a73715ebc3fb

1 files changed, 4 insertions, 5 deletions

diff --git a/source/blender/blenlib/BLI_math_rotation.h b/source/blender/blenlib/BLI_math_rotation.h
index fef51fa780e..3987c9daf0a 100644
--- a/source/blender/blenlib/BLI_math_rotation.h
+++ b/source/blender/blenlib/BLI_math_rotation.h
@@ -177,10 +177,9 @@ void mat3_to_quat_is_ok(float q[4], const float mat[3][3]);
 /* Other. */
 
 /**
- * Utility function that performs `sinf` & `cosf` where the quadrants of the circle
- * will have exactly matching values when their sign is flipped.
- * This works as long as the denominator can be divided by 2 or 4,
- * otherwise `sinf` & `cosf` are used without any additional logic.
+ * Utility that performs `sinf` & `cosf` intended for plotting a 2D circle,
+ * where the values of the coordinates with are exactly symmetrical although this
+ * favors even numbers as odd numbers can only be symmetrical on a single axis.
  *
  * Besides adjustments to precision, this function is the equivalent of:
  * \code {.c}
@@ -194,7 +193,7 @@ void mat3_to_quat_is_ok(float q[4], const float mat[3][3]);
  * \param r_sin: The resulting sine.
  * \param r_cos: The resulting cosine.
  */
-void sin_cos_from_fraction(const int numerator, const int denominator, float *r_sin, float *r_cos);
+void sin_cos_from_fraction(int numerator, int denominator, float *r_sin, float *r_cos);
 
 void print_qt(const char *str, const float q[4]);