FTB_MSB

Format: FTB_MSB dest, source.

Phase0: FTB_MSB FT3, (FT2)

Phase1: -

Phase2: -

Description: Find top bit set, starting from the MSB – Where result is MSB=0 down to LSB=31

Return -1 if no bits set.
Table 1. Example:
If((unsigned)ft2 ==0)
    FT3 = -1
else
    c=31;
while ((unsigned)ft2>>32-c) --c;
    FT3=c;