  Conversion between binary and decimal floating-point representations is
ubiquitous. Floating-point radix conversion means converting both the exponent
and the mantissa. We develop an atomic operation for FP radix conversion with
simple straight-line algorithm, suitable for hardware design. Exponent
conversion is performed with a small multiplication and a lookup table. It
yields the correct result without error. Mantissa conversion uses a few
multiplications and a small lookup table that is shared amongst all types of
conversions. The accuracy changes by adjusting the computing precision.
