The BBC and Master Computer Public Domain Library

Load IWA with Integer from Zero Page Address

Submitted by Steve Fewell

Routine: izpin
Name: Load IWA with Integer from Zero Page Address
Starting Address: &AA80
Entry criteria: X is the Zero page address of the Least Significant (first) byte of a 32-bit Integer variable
Exit: IWA contains the Integer number pointed to by X (That is the 32-bit Integer stored in locations 00,X to 03,X).

Description:
Loads the IWA with the 32-bit Integer pointed to by the X register (The number is stored least significant byte first, one byte is copied at a time), and sets A to #&40 to show that an Integer number is being processed.

There is another routine which loads the IWA from any address, but we need this zero page routine due to it executing a lot faster than the one which allows longer addresses.

Disassembly for the Load Integer from Zero Page Address routine