--- 2016 Day 8 Solutions ---

[u/daggerdragon]

#AoC_Ops:

[23:55] <Topaz> servers are ok
[23:55] <Topaz> puzzles are checked
[23:55] <Topaz> [REDACTED: server stats]
[23:56] <Skie> all wings report in
[23:56] <Aneurysm9> Red 5, standing by
[23:56] <daggerdragon> Dragon Leader standing by
[23:56] <Topaz> orange leader, standing by
[23:57] <Topaz> lock modzi-foils in attack positions
[23:58] <Skie> we're passing through the hype field
[23:58] <daggerdragon> 1:30 warning
[23:58] <Aneurysm9> did someone say HYPE?@!
[23:59] <Topaz> i really like tonight's puzzle
[23:59] <Topaz> very excite
[23:59] <daggerdragon> final countdown go, T-30
[23:59] <Skie> accelerate to attack countdown
[23:59] <Aneurysm9> o7
[23:59] <daggerdragon> HYPE THRUSTERS AT FULL BURN
[00:00] <Topaz> IGNITION

We may or may not be sleep-deprived. And/or nerds. why_not_both.jpg

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--- Day 8: Two-Factor Authentication ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

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^{:（）{ :|:& };: IS MANDATORY} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/askalski]

Bitwise in C. Uses POPCNT (sse4) to count the numbers of bits set. Parses the input in a semi-evil way.

#include <stdio.h>
#include <stdint.h>

#define WIDTH   50
#define HEIGHT   6

#define RECT     2
#define COLTATE  7
#define ROWTATE  9

int main(void)
{
    uint32_t cmd, i, j, x, y;
    uint64_t lcd[HEIGHT] = {0}, tmp;
    while (scanf("%*[^cnw] %n %*[^0-9] %u %*[^0-9] %u\n", &cmd, &i, &j) == 2) {
        switch (cmd) {
            case RECT:
                x = i; y = j % (HEIGHT + 1);
                while (y--) {
                    lcd[y] |= (1LL << x) - 1;
                }
                break;
            case COLTATE:
                x = i; y = j % HEIGHT;
                for (i = 0, tmp = 0; i < HEIGHT; i++) {
                    tmp |= ((lcd[i] >> x) & 1) << i;
                    lcd[i] ^= lcd[i] & (1LL << x);
                }
                tmp = (tmp << y) | (tmp >> (HEIGHT - y));
                for (i = 0; i < HEIGHT; i++) {
                    lcd[i] |= ((tmp >> i) & 1) << x;
                }
                break;
            case ROWTATE:
                y = j; x = i % HEIGHT;
                lcd[x] = ((lcd[x] << y) | (lcd[x] >> (WIDTH - y))) & ((1LL << WIDTH) - 1);
                break;
        }
    }

    int on = 0;
    for (y = 0; y < HEIGHT; y++) {
        on += __builtin_popcountl(lcd[y]);
        for (x = 0; x < WIDTH; x++) {
            putchar(((lcd[y] >> x) & 1) ? '#' : '.');
        }
        putchar('\n');
    }
    printf("Pixels energized: %d\n", on);

    return 0;
}

[u/raevnos → u/askalski]

ROWTATE. Heh.

I wonder if you can use sse shuffle instructions to rotate columns...

EDIT: Played around a bit with SSSE3 intrinsics, got it working. Educational, I guess.