From c390bbef2ab0a203977a8e034f76f4df15be8a13 Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Mon, 17 Dec 2018 15:56:51 -0500
Subject: Solve day 16 part 1

---
 2018/day16.c | 132 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)
 create mode 100644 2018/day16.c

diff --git a/2018/day16.c b/2018/day16.c
new file mode 100644
index 0000000..a1a72c4
--- /dev/null
+++ b/2018/day16.c
@@ -0,0 +1,132 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef unsigned uint;
+typedef unsigned short Set;
+
+struct CPU {
+	uint r[4];
+};
+
+static int cpuEq(struct CPU a, struct CPU b) {
+	return a.r[0] == b.r[0]
+		&& a.r[1] == b.r[1]
+		&& a.r[2] == b.r[2]
+		&& a.r[3] == b.r[3];
+}
+
+typedef struct CPU Op(struct CPU, uint, uint, uint);
+
+static struct CPU addr(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] + cpu.r[b]; return cpu;
+}
+static struct CPU addi(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] + b; return cpu;
+}
+static struct CPU mulr(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] * cpu.r[b]; return cpu;
+}
+static struct CPU muli(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] * b; return cpu;
+}
+static struct CPU banr(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] & cpu.r[b]; return cpu;
+}
+static struct CPU bani(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] & b; return cpu;
+}
+static struct CPU borr(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] | cpu.r[b]; return cpu;
+}
+static struct CPU bori(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] | b; return cpu;
+}
+static struct CPU setr(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a]; return cpu;
+}
+static struct CPU seti(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = a; return cpu;
+}
+static struct CPU gtir(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = a > cpu.r[b]; return cpu;
+}
+static struct CPU gtri(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] > b; return cpu;
+}
+static struct CPU gtrr(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] > cpu.r[b]; return cpu;
+}
+static struct CPU eqir(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = a == cpu.r[b]; return cpu;
+}
+static struct CPU eqri(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] == b; return cpu;
+}
+static struct CPU eqrr(struct CPU cpu, uint a, uint b, uint c) {
+	cpu.r[c] = cpu.r[a] == cpu.r[b]; return cpu;
+}
+
+static const struct {
+	const char *name;
+	Op *fn;
+} Ops[16] = {
+	{ "addr", addr },
+	{ "addi", addi },
+	{ "mulr", mulr },
+	{ "muli", muli },
+	{ "banr", banr },
+	{ "bani", bani },
+	{ "borr", borr },
+	{ "bori", bori },
+	{ "setr", setr },
+	{ "seti", seti },
+	{ "gtir", gtir },
+	{ "gtri", gtri },
+	{ "gtrr", gtrr },
+	{ "eqir", eqir },
+	{ "eqri", eqri },
+	{ "eqrr", eqrr },
+};
+
+static uint card(Set set) {
+	uint pop = 0;
+	while (set) {
+		if (set & 1) pop++;
+		set >>= 1;
+	}
+	return pop;
+}
+
+int main(void) {
+	Set opcodes[16];
+	for (uint i = 0; i < 16; ++i) {
+		opcodes[i] = 0xFFFF;
+	}
+
+	uint samples = 0;
+	for (;;) {
+		struct CPU before, after;
+		uint code, a, b, c;
+		int match = scanf(
+			"Before: [%u, %u, %u, %u]\n"
+			"%u %u %u %u\n"
+			"After: [%u, %u, %u, %u]\n",
+			&before.r[0], &before.r[1], &before.r[2], &before.r[3],
+			&code, &a, &b, &c,
+			&after.r[0], &after.r[1], &after.r[2], &after.r[3]
+		);
+		if (match < 12) break;
+
+		uint count = 0;
+		for (uint i = 0; i < 16; ++i) {
+			struct CPU result = Ops[i].fn(before, a, b, c);
+			if (cpuEq(result, after)) {
+				count++;
+			} else {
+				opcodes[code] &= ~(1 << i);
+			}
+		}
+		if (count >= 3) samples++;
+	}
+	printf("%u\n", samples);
+}
-- 
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