From 881cdd6e3243221fbe3acb2e40517dc858fb8e1e Mon Sep 17 00:00:00 2001
From: Nick Thomas <me@ur.gs>
Date: Fri, 6 Dec 2019 00:44:48 +0000
Subject: [PATCH] Day 5.2

---
 05/src/main.zig         | 22 +++++++++++++-----
 lib/intcode/intcode.zig | 50 ++++++++++++++++++++++++++++++++++++++---
 2 files changed, 64 insertions(+), 8 deletions(-)

diff --git a/05/src/main.zig b/05/src/main.zig
index ae55384..dee0a3a 100644
--- a/05/src/main.zig
+++ b/05/src/main.zig
@@ -7,14 +7,26 @@ pub fn main() anyerror!void {
 
     const alloc = &arena.allocator;
 
-    var program = try intcode.loadFromStdIn(alloc);
-    var machine = try intcode.Machine.init(alloc, program);
+    var p1 = try intcode.loadFromStdIn(alloc);
+    var p2 = try alloc.alloc(i32, p1.len);
+    std.mem.copy(i32, p2, p1);
 
-    try machine.input.append(1); // Air conditioner unit
-    try machine.run();
+    var m1 = try intcode.Machine.init(alloc, p1);
+    var m2 = try intcode.Machine.init(alloc, p2);
 
     std.debug.warn("Part 1\n");
-    for (machine.output.toSlice()) |value, idx| {
+    try m1.input.append(1); // Air conditioner unit
+    try m1.run();
+
+    for (m1.output.toSlice()) |value, idx| {
+        std.debug.warn("Test {}: {}\n", idx, value);
+    }
+
+    std.debug.warn("\nPart 2\n");
+    try m2.input.append(5); // Thermal radiator controller
+    try m2.run();
+
+    for (m2.output.toSlice()) |value, idx| {
         std.debug.warn("Test {}: {}\n", idx, value);
     }
 }
diff --git a/lib/intcode/intcode.zig b/lib/intcode/intcode.zig
index 50460ca..039fc20 100644
--- a/lib/intcode/intcode.zig
+++ b/lib/intcode/intcode.zig
@@ -35,6 +35,10 @@ const Opcode = enum(u8) {
     MULT = 2,
     IN = 3,
     OUT = 4,
+    JNZ = 5,
+    JZ = 6,
+    LT = 7,
+    EQ = 8,
     END = 99,
 };
 
@@ -73,6 +77,10 @@ const Instruction = struct {
             .MULT => 4,
             .IN => 2,
             .OUT => 2,
+            .JNZ => 3,
+            .JZ => 3,
+            .LT => 4,
+            .EQ => 4,
             .END => 1,
         };
     }
@@ -127,8 +135,8 @@ pub const Machine = struct {
     }
 
     pub fn step(self: *Machine) anyerror!bool {
-        var program = self.memory;
-        const insn = try Instruction.decode(program[self.ip]);
+        const insn = try Instruction.decode(self.memory[self.ip]);
+        const start_ip = self.ip;
 
         const opcode = switch (insn.op) {
             .ADD => {
@@ -148,13 +156,49 @@ pub const Machine = struct {
             .IN => {
                 self.__write(0, self.input.orderedRemove(0));
             },
+
             .OUT => {
                 try self.output.append(self.__read(0, insn.modes[0]));
             },
+
+            .JNZ => {
+                if (self.__read(0, insn.modes[0]) != 0)
+                    self.ip = @intCast(usize, self.__read(1, insn.modes[1]));
+            },
+
+            .JZ => {
+                if (self.__read(0, insn.modes[0]) == 0)
+                    self.ip = @intCast(usize, self.__read(1, insn.modes[1]));
+            },
+
+            .LT => {
+                const a = self.__read(0, insn.modes[0]);
+                const b = self.__read(1, insn.modes[1]);
+
+                if (a < b) {
+                    self.__write(2, 1);
+                } else {
+                    self.__write(2, 0);
+                }
+            },
+
+            .EQ => {
+                const a = self.__read(0, insn.modes[0]);
+                const b = self.__read(1, insn.modes[1]);
+
+                if (a == b) {
+                    self.__write(2, 1);
+                } else {
+                    self.__write(2, 0);
+                }
+            },
+
             .END => {},
         };
 
-        self.ip += insn.size();
+        // Only modify IP if the instruction itself has not
+        if (self.ip == start_ip) self.ip += insn.size();
+
         return !insn.halt();
     }
 };