diff --git a/2019/input/day5.txt b/2019/input/day5.txt
new file mode 100644
index 0000000..e659ce6
--- /dev/null
+++ b/2019/input/day5.txt
@@ -0,0 +1 @@
+3,225,1,225,6,6,1100,1,238,225,104,0,1101,61,45,225,102,94,66,224,101,-3854,224,224,4,224,102,8,223,223,1001,224,7,224,1,223,224,223,1101,31,30,225,1102,39,44,224,1001,224,-1716,224,4,224,102,8,223,223,1001,224,7,224,1,224,223,223,1101,92,41,225,101,90,40,224,1001,224,-120,224,4,224,102,8,223,223,1001,224,1,224,1,223,224,223,1101,51,78,224,101,-129,224,224,4,224,1002,223,8,223,1001,224,6,224,1,224,223,223,1,170,13,224,101,-140,224,224,4,224,102,8,223,223,1001,224,4,224,1,223,224,223,1101,14,58,225,1102,58,29,225,1102,68,70,225,1002,217,87,224,101,-783,224,224,4,224,102,8,223,223,101,2,224,224,1,224,223,223,1101,19,79,225,1001,135,42,224,1001,224,-56,224,4,224,102,8,223,223,1001,224,6,224,1,224,223,223,2,139,144,224,1001,224,-4060,224,4,224,102,8,223,223,101,1,224,224,1,223,224,223,1102,9,51,225,4,223,99,0,0,0,677,0,0,0,0,0,0,0,0,0,0,0,1105,0,99999,1105,227,247,1105,1,99999,1005,227,99999,1005,0,256,1105,1,99999,1106,227,99999,1106,0,265,1105,1,99999,1006,0,99999,1006,227,274,1105,1,99999,1105,1,280,1105,1,99999,1,225,225,225,1101,294,0,0,105,1,0,1105,1,99999,1106,0,300,1105,1,99999,1,225,225,225,1101,314,0,0,106,0,0,1105,1,99999,1008,677,226,224,102,2,223,223,1006,224,329,101,1,223,223,108,677,677,224,102,2,223,223,1005,224,344,101,1,223,223,107,677,677,224,1002,223,2,223,1005,224,359,101,1,223,223,1107,226,677,224,1002,223,2,223,1005,224,374,1001,223,1,223,1008,677,677,224,102,2,223,223,1006,224,389,1001,223,1,223,1007,677,677,224,1002,223,2,223,1006,224,404,1001,223,1,223,8,677,226,224,102,2,223,223,1005,224,419,1001,223,1,223,8,226,226,224,102,2,223,223,1006,224,434,101,1,223,223,1107,226,226,224,1002,223,2,223,1006,224,449,101,1,223,223,1107,677,226,224,102,2,223,223,1005,224,464,101,1,223,223,1108,226,226,224,102,2,223,223,1006,224,479,1001,223,1,223,7,677,677,224,1002,223,2,223,1006,224,494,101,1,223,223,7,677,226,224,102,2,223,223,1005,224,509,101,1,223,223,1108,226,677,224,1002,223,2,223,1006,224,524,101,1,223,223,8,226,677,224,1002,223,2,223,1005,224,539,101,1,223,223,1007,226,226,224,102,2,223,223,1006,224,554,1001,223,1,223,108,226,226,224,1002,223,2,223,1006,224,569,1001,223,1,223,1108,677,226,224,102,2,223,223,1005,224,584,101,1,223,223,108,226,677,224,102,2,223,223,1005,224,599,101,1,223,223,1007,226,677,224,102,2,223,223,1006,224,614,1001,223,1,223,1008,226,226,224,1002,223,2,223,1006,224,629,1001,223,1,223,107,226,226,224,1002,223,2,223,1006,224,644,101,1,223,223,7,226,677,224,102,2,223,223,1005,224,659,1001,223,1,223,107,677,226,224,102,2,223,223,1005,224,674,1001,223,1,223,4,223,99,226
diff --git a/2019/src/computer.rs b/2019/src/computer.rs
new file mode 100644
index 0000000..10a6150
--- /dev/null
+++ b/2019/src/computer.rs
@@ -0,0 +1,129 @@
+type Address = i32;
+
+#[derive(Debug, Eq, PartialEq)]
+enum Instruction {
+    Add(Mode, Mode),
+    Multiply(Mode, Mode),
+    Input(Mode),
+    Output(Mode),
+    Halt,
+}
+
+#[derive(Debug, Eq, PartialEq)]
+enum Mode {
+    Immediate,
+    Address,
+}
+
+struct Memory<'a> {
+    mem: &'a mut [i32],
+}
+
+fn decode(mut instruction: i32) -> Instruction {
+    let opcode = divmod(&mut instruction, 100);
+
+    match opcode {
+        1 => {
+            // let mode3 = divmod(&mut instruction, 10);
+            // Parameters that an instruction writes to will never be in immediate mode.
+            Instruction::Add(
+                Mode::from(divmod(&mut instruction, 10)),
+                Mode::from(divmod(&mut instruction, 10)),
+            )
+        }
+        2 => Instruction::Multiply(
+            Mode::from(divmod(&mut instruction, 10)),
+            Mode::from(divmod(&mut instruction, 10)),
+        ),
+        3 => Instruction::Input(Mode::from(divmod(&mut instruction, 10))),
+        4 => Instruction::Output(Mode::from(divmod(&mut instruction, 10))),
+        99 => Instruction::Halt,
+        _ => panic!("Invalid opcode: {}", opcode),
+    }
+}
+
+impl<'a> Memory<'a> {
+    pub fn new(mem: &'a mut [i32]) -> Self {
+        Memory { mem }
+    }
+
+    pub fn read(&self, value: i32, mode: Mode) -> i32 {
+        match mode {
+            Mode::Immediate => value,
+            Mode::Address => self.mem[value as usize],
+        }
+    }
+
+    fn write(&mut self, address: Address, value: i32) {
+        self.mem[address as usize] = value;
+    }
+
+    fn run(&mut self, noun: i32, verb: i32) {
+        self.write(1, noun);
+        self.write(2, verb);
+        let mut ip = 0; // instruction pointer
+
+        loop {
+            match decode(self.read(ip, Mode::Address)) {
+                Instruction::Add(mode1, mode2) => {
+                    let result = self.read(ip + 1, mode1) + self.read(ip + 1, mode2);
+                    self.write(ip + 3, result);
+                    ip += 4;
+                }
+                Instruction::Multiply(mode1, mode2) => {
+                    let result = self.read(ip + 1, mode1) * self.read(ip + 1, mode2);
+                    self.write(ip + 3, result);
+                    ip += 4;
+                }
+                Instruction::Input(mode) => {
+                    ip += 2;
+                }
+                Instruction::Output(mode) => {
+                    ip += 2;
+                }
+                Instruction::Halt => break,
+            }
+        }
+    }
+}
+
+fn divmod(value: &mut i32, divisor: i32) -> i32 {
+    let res = *value % divisor;
+    *value /= divisor;
+    res
+}
+
+impl From<i32> for Mode {
+    fn from(mode: i32) -> Self {
+        match mode {
+            0 => Mode::Address,
+            1 => Mode::Immediate,
+            _ => unreachable!(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::input;
+    use std::fs;
+
+    #[test]
+    fn test_decode() {
+        assert_eq!(
+            decode(1002),
+            Instruction::Multiply(Mode::Address, Mode::Immediate)
+        )
+    }
+
+    fn test_day2() {
+        let input = fs::read_to_string("input/day2.txt").unwrap();
+        let mut data = input::read_separated_line(',', &input).unwrap();
+        let mut program = Memory::new(&mut data);
+
+        // Check that day2 still works wirh run through this implementation
+        program.run(12, 2);
+        assert_eq!(program.read(0, Mode::Address), 4138658);
+    }
+}
diff --git a/2019/src/lib.rs b/2019/src/lib.rs
index 3a6660f..2e7a87e 100644
--- a/2019/src/lib.rs
+++ b/2019/src/lib.rs
@@ -1,2 +1,3 @@
+pub mod computer;
 pub mod input;
 pub mod point;