Tables in the stack

In front of the smelter stands an input locker. Only ores may go in, anything else should trigger a warning lamp. Which ores are allowed is stored in a table in the stack. The chip searches it for the item in the slot.

Computing the index#

A table starts at a fixed address, the start. Entry number i sits at start + i:

define TABLE 10 # first address of the table
add adr TABLE i
get entry db adr

Do not let the table start at 0 if you also use push. A fixed start such as 10 or 400 keeps it away from the push pile. And whoever needs a second table later simply puts it behind the first.

Loop over the entries#

Filling happens once before the start label, with a moving address:

move adr TABLE
poke adr IRON
add adr adr 1
poke adr COPPER

Reading happens in a loop with a counter, as you know it from the slots:

move i 0
search:
bge i COUNT done           # all entries done
add adr TABLE i
get entry db adr
beq item entry found       # match: out at once
add i i 1
j search

Searching values#

The search above stops at the first match. That saves instructions, especially with long tables. Prefab hashes are whole numbers, so the exact comparison with beq is right here. With readings it would not be.

Other searches follow the same pattern: find the largest element (with max over all entries), remember the position of a value (keep i on a match), count how often something occurs.