08-zebros-copies-point-of-sale-system

8: Zebros Copies (Point-Of-Sale System)

Instructions

Erase Ghast's debt to the copy shop by zeroing out his balance in the customer database (file 200) and appending a payment to the payment log (file 201) with today's date and the exact amount of his prior balance.

Ghast's customer ID is available in file 300.

For more information see "Network Exploration: Digicash Point-of-Sale Systems" in the first issue of the zine.

Solution

XA (global)

GRAB 300
COPY F M
SEEK -1
COPY F M
WIPE

XB (global)

LINK 800
GRAB 200
COPY M X
MARK LOOP
TEST F = X
FJMP LOOP
COPY F X
COPY F T
SEEK -2
COPY 0 F
COPY 0 F
DROP
GRAB 201
SEEK 9999
COPY X F
COPY T F
DROP
WIPE

XC (global)

LINK 800
LINK 801
COPY #DATE X
COPY M T
LINK -1
GRAB 201
SEEK 9999
COPY X F
COPY T F
DROP
WIPE

Results

Cycles	Size	Activity
102	34	4