The BBC and Master Computer Public Domain Library
Clear FWA
Submitted by Steve Fewell
Routine: aclear
Name: Clear FWA
Starting Address: &A6B4
Entry criteria: None
Exit: Every byte in the FWA contains the
value 0 (this indicates the number 0).
Description:
Sets every byte of the FWA (locations &2E to &35) to zero. This uniquely
identifies the number zero.
This routine can be jumped in at address A6B8, in this case all bytes of the FWA are cleared, except for the Exponent and Mantissa byte 1 (the most significant byte of the mantissa).
Disassembly for the Clear FWA routine
| A6B4 | d0 | 100 048 | 64 30 | STZ &30 |
| A6B6 | d1 | 100 049 | 64 31 | STZ &31 |
| A6B8 | d. | 100 046 | 64 2E | STZ &2E |
| A6BA | d/ | 100 047 | 64 2F | STZ &2F |
| A6BC | d2 | 100 050 | 64 32 | STZ &32 |
| A6BE | d3 | 100 051 | 64 33 | STZ &33 |
| A6C0 | d4 | 100 052 | 64 34 | STZ &34 |
| A6C2 | d5 | 100 053 | 64 35 | STZ &35 |
| A6C4 | ` | 096 | 60 | RTS |
