This normalization was added in 02ac5e95c8, and changed to use floats in 4bf031c064. The conversion to floats means that sometimes there is insufficient precision for the normalization process, which results in values of NaN or infinity. Performing the whole process with doubles prevents that, but games also sometimes set the values to NaN or infinity directly (possibly accidentally due to the values not being initialized due to them not being used in the current configuration?).
The version of Mesa currently in use on FifoCI (20.3.5) has issues with NaN. Although this bug has been fixed (b3f3287eac in 21.2.0), FifoCI is stuck with the older version.
This change may or may not be incorrect, but it should result in the same behavior as already present in Dolphin, while working around the Mesa bug.
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