Setting the Rounding Precision

Set corresponding to each operation.
Straightforward implementation.

×  Not efficient.
This way involves frequent re-setting of the rounding precision.
Setting causes memory (cache) access.

cf.  SPARC and MIPS have instructions corresponding to each precision.
SPARC has fmuls and fmuld.
MIPS has mul.s and mul.d.

We'd like to avoid this inefficiency...