-move a 32-bit float from a GPR to a FPR, just copying bits of the IEEE 754
-representation directly. This is equivalent to `stw` followed by `lfs`.
-As `fmvfgs` is just copying bits, `FPSCR` is not affected in any way.
+Move a BFP32 from a GPR to a FPR, by using `DOUBLE` on the least significant
+32-bits of RB to do the standard BFP32 in BFP64 trick and store the result in
+FRT. This is equivalent to `stw` followed by `lfs`.
+As `fmvfgs` is just copying the BFP32 form, `FPSCR` is not affected in any way.