The BBC and Master Computer Public Domain Library

Clear FWB

Submitted by Steve Fewell

Routine: bclear
Name: Clear FWB
Starting Address: &A570
Entry criteria: None
Exit: Every byte in the FWB contains the value 0 (this indicates the number 0).

Description:
Sets every byte of the FWB (locations &3B to &41) to zero. This uniquely identifies the number zero.

This routine can be jumped in at address A576, in this case all bytes of the FWB are cleared, except for the Sign, Exponent and Mantissa byte 1 (the most significant byte of the mantissa).

Disassembly for the Clear FWB routine