The avatar for @emanuelfeld
Emanuel Feld
Published
Advent of Code 2018
Edited
Dec 23, 2018
Advent of Code 2018
[Day 25](https://adventofcode.com/2018/day/25)[Day 18](https://adventofcode.com/2018/day/18)
[Day 21](https://adventofcode.com/2018/day/21)
Day 19[Day 16](https://adventofcode.com/2018/day/16)[Day 14](https://adventofcode.com/2018/day/14)[Day 13](https://adventofcode.com/2018/day/13)[Day 12](https://adventofcode.com/2018/day/12)[Day 11](https://adventofcode.com/2018/day/11)[Day 10](https://adventofcode.com/2018/day/10)[Day 9](https://adventofcode.com/2018/day/9)[Day 8](https://adventofcode.com/2018/day/8)[Day 7](https://adventofcode.com/2018/day/7)[Day 6](https://adventofcode.com/2018/day/6)[Day 5](https://adventofcode.com/2018/day/5)[Day 4](https://adventofcode.com/2018/day/4)[Day 3](https://adventofcode.com/2018/day/3)Advent of Code: [Day 2](https://adventofcode.com/2018/day/2)[Day 1](https://adventofcode.com/2018/day/1)
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part1 = {
let register = [0, 0, 0, 0, 0, 0];

while (register[IP_REGISTER] < INSTRUCTIONS.length && register[IP_REGISTER] >= 0) {
if (register[IP_REGISTER] === 28) {
return register[5];
}

const [currentInstruction, a, b, c] = INSTRUCTIONS[register[IP_REGISTER]];
calculate[currentInstruction](register, a, b, c);
register[IP_REGISTER]++;
}
}
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part2 = {
// Too slow to run in browser without reverse engineering the ElfCode
let B, E;
let prev;
let seen = new Set();
B = 65536;
E = 7571367;

while (true) {
E += B & 255;
E &= 16777215;
E *= 65899;
E &= 16777215;

if (B < 256) {
// Find the last new value of E during instruction 28 before it cycles
// That will be the last hit, so setting r[0] to its value results
// in the most instructions among all possible terminating values.
if (seen.has(E)) {
return prev;
} else {
seen.add(E);
prev = E;
}
B = E | 65536;
E = 7571367;
} else {
B = Math.floor(B / 256);
}
}
}
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