The BBC and Master Computer Public Domain Library

A027 '^' Operator (raise FWA to the Power)

Submitted by Steve Fewell

Description:

Convert value to a Float if it is an Integer. If it is a String, then Type mismatch error.
Push FWA to the Stack.
Obtain second value, convert to Float if it is an Integer. If it is a String, then Type
mismatch error.
If the FWA exponent of the Power value is less than #&87 then do the following:
 *   Call &82E0 to Split the FWA into an Integer value (&49) and a Fractional
     value (FWA).
 *   If the Fractional Part of the FWA is 0.00 then Pop the Float back from Stack to the FWA;
     call &A5BE to raise the FWA to the power of the Integer in &49; and
     return to level 6 of the expression handler with FWA = the result.
 *   Otherwise, store the fractional power value in the Temporary Floating-Point variable at &0476.
 *   Unpack the Float value from the Stack (without popping it, as we will pop it later) into the FWA.
 *   Raise the FWA to the Integer Part of the Power value (&49).

Otherwise, If the FWA exponent of the Power value is >= #&87 then do the following:
 *   Store the Power value (in the FWA) in the Temporary Floating-Point variable at &0476.
 *   Set the FWA = 1.0.

Now we have the power value in &0476 and the FWA set to any result calculated so far.
Next, store the result calculated so far (in the FWA) to Temporary Floating-Point variable at &0471.
Pop the Float from the Stack (the first value - that is the value to raise to the power) to the FWA.
Call LN routine to get the natural logorithm of the Float value.
Multiply the natural logorithm result with the Float Power value (&0476).
Call EXP routine to obtain the exponental of this result.
This gives us the first value raised to the power of the Float Power value.

Next, we need to multiply this result by any result we have already calculated (in &0471),
as the Integer part of the power may have already been calculated separately.
Lastly, exit with A = #&FF (as we have a Floating-Point result).

Disassembly for the '^' Operator routine