BASIC IV ROM Routines
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Submitted by Steve Fewell
Routine: acomp
Name: Floating-Point Compliment
Starting Address: &ACCA
Entry criteria: The FWA contains a
floating-point number.
Exit: FWA has been complimented (FWA =
zero - FWA)
Description:
If the FWA Mantissa byte 1 (Most significant byte) contains zero - indicating
that the current number in the FWA is zero, then exit as no further operation
required.
Otherwise, Exclusive-OR the FWA Sign Byte with 10000000 (&80). This reverses the Most significant Bit of the Sign Byte (so 0 becomes 1, and 1 becomes 0). Then exit with A = 255 (&FF) indicating that a Floating-Point value has just been processed.
Disassembly for the Floating-Point Compliment routine
| ACCA | 1 | 165 049 | A5 31 | LDA &31 |
| ACCC | 240 006 | F0 06 | BEQ 6 --> &ACD4 | |
| ACCE | . | 165 046 | A5 2E | LDA &2E |
| ACD0 | I | 073 128 | 49 80 | EOR#&80 |
| ACD2 | . | 133 046 | 85 2E | STA &2E |
| ACD4 | 169 255 | A9 FF | LDA#&FF | |
| ACD6 | ` | 096 | 60 | RTS |
