SignalChapter 3: Chains and rings

14EDGE DETECTOR

The task

P must receive 1 when a value is 10 or more away from the one before it, else 0.

The value before the first is 0. MOV A, 1 puts a 1 in A.

The board

The board as the puzzle screen lays it out. Cyan pins read, lemon pins write, violet pins go both ways. On a narrow screen, scroll the board sideways to see all of it.

Key idea

Old and new value at one core, then a two sided test.

Hints

Each hint goes a step further than the one before. Open them one at a time.

Hint 1Show

The difference needs the new value and the old one at the same core.

Hint 2Show

XCH after IN keeps the new value in B and brings the old one into A.

Hint 3Show

A negative difference is as far as a positive one. JG, then NEG.

Solution

Reveal the Full SolutionThe complete program for EDGE DETECTOR. Open it only when you want the answer.

The reference program

The game's own solution. It passes every test and scores exactly par on every benchmark.

c0SC-2 standard

IN P0
OUT P1

c2SC-2 standard

T: IN P0
XCH A, B
SUB B
JG G
NEG
G: SUB 10
JL N
MOV A, 1
OUT P2
JMP T
N: MOV A, 0
OUT P2

CYCLES: 406; at par
ENERGY: 2616; at par
NODES: 2; at par
INSTRUCTIONS: 14; at par

Another way: Fork

A second program that also passes, by a different road, at a cost on CYCLES, ENERGY, NODES, and INSTRUCTIONS.

The fork: one path delays the stream by one, so old and new meet at the right core.

c0SC-2 standard

IN P0
OUT P1
OUT P2

c1SC-2 standard

OUT P1
IN P0

c2SC-2 standard

IN P0
MOV B, A
IN P1
SUB B
JG G
NEG
G: SUB 10
JL N
MOV A, 1
JMP O
N: MOV A, 0
O: OUT P2

CYCLES: 446; over par
ENERGY: 3558; over par
NODES: 3; over par
INSTRUCTIONS: 17; over par