The BBC and Master Computer Public Domain Library

A5BE Raise the FWA to the Power of the Integer Value in A

Submitted by Steve Fewell

Description:

If the Integer power (A) is negative then decrement if and EOR it with #&FF to
reverse the two's complement and obtain the absolute value of the power. Then call
the Floating-Point Reciple routine (&A5E9) to set FWA = 1/FWA. Now the FWA can be raised
to the positive power value to give the required result.

If the Integer power is 0, then set FWA = 1.0 and exit.

Store the FWA to Temporary Floating-Point variable location &046C.
If the power = 1 then exit (the FWA already contains the result, as raising to the power
of 1 just returns the same value).

Reduce the power value by 1.
Keep multiplying the FWA by the original copy of the FWA (&046C) (FWA = &046C * FWA)
and reducing the power value until the power value is zero.
Exit, as the FWA now contains the correct result of FWA^A.

Note: It's strange that there is no quicker way to perform this calculation!

Disassembly for the Raise FWA to Power of 'A' value routine