A new train is being developed which includes a sensor to detect passengers entering and exiting carriages to be aware of the comfort level of our customers.
We want to develop a simple chip to keep track of the available seats on the carriage.
The controller will emit assembly istructions that we need to execute.
The CPU has 3 registers: a, b, c
Example:
mov 42 a
dec a
dec a
inc a
inc a
dec a
We initialize at 42 seats. 2 passengers enter, then both leave and one new passenger enter. So we have 41 available seats.
mov x ycopies x (either an integer or the value of a register) into register y.inc xincreases the value of register x by one.dec xdecreases the value of register x by one.
The train has 2 carriages.
If we assume we are keeping track of the available seats of the two carriages in register a and b,
we want to be able on demand to get the total of available seats on the whole train on the register c.
We have an extra istruction we can use:
jnz x y jumps to an instruction y away (positive means forward; negative means backward), but only if x is not zero.
The jnz instruction moves relative to itself: an offset of -1 would continue at the previous instruction, while an offset of 2 would skip over the next instruction.