xr_linear.h XrQuaternionf_Multiply(r, a, b) returns product of b * a not a * b.

Looking at the signs of the cross terms they reflect the commuted order of multiplication.

As there doesn't appear to be either unit test, nor documentation it's not clear if this is intended behavior and simply undocumented, or whether it's simply an error (or something I don't understand ).

Also, as this function is called from several other locations within the header, it's not clear as to their correctness.

Start in xr_linear.h at XrQuaternionf_Multiply and inspect every call site in the header, comparing the cross-term signs and operand order. Determine whether the documented or intended convention is a * b; done means the behavior is confirmed or corrected consistently, with the convention documented and covered by tests.

Written by the indexing model from the issue text.