From c294af6f1de621199c9d069d92679ef7a9f8aaa0 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Mon, 18 Dec 2017 13:23:56 +0100
Subject: [PATCH] Implement day 18 in Lua.

---
 2017/README.md           |   1 +
 2017/day-18/input.txt    |  41 ++++++++++
 2017/day-18/solution.lua | 160 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 202 insertions(+)
 create mode 100644 2017/day-18/input.txt
 create mode 100755 2017/day-18/solution.lua

diff --git a/2017/README.md b/2017/README.md
index dc0209c..fe20231 100644
--- a/2017/README.md
+++ b/2017/README.md
@@ -19,6 +19,7 @@ The current plan, in no particular order:
 - [ ] Java
 - [x] Kotlin - [Day 10](./day-10/solution.kt)
 - [x] Lex - [Day 09](./day-09/solution.l)
+- [x] Lua - [Day 18](./day-18/solution.lua)
 - [x] Matlab - [Day 06](./day-06)
 - [x] Node.js - [Day 12](./day-12/solution.js)
 - [ ] Objective C
diff --git a/2017/day-18/input.txt b/2017/day-18/input.txt
new file mode 100644
index 0000000..8b74206
--- /dev/null
+++ b/2017/day-18/input.txt
@@ -0,0 +1,41 @@
+set i 31
+set a 1
+mul p 17
+jgz p p
+mul a 2
+add i -1
+jgz i -2
+add a -1
+set i 127
+set p 735
+mul p 8505
+mod p a
+mul p 129749
+add p 12345
+mod p a
+set b p
+mod b 10000
+snd b
+add i -1
+jgz i -9
+jgz a 3
+rcv b
+jgz b -1
+set f 0
+set i 126
+rcv a
+rcv b
+set p a
+mul p -1
+add p b
+jgz p 4
+snd a
+set a b
+jgz 1 3
+snd b
+set f 1
+add i -1
+jgz i -11
+snd a
+jgz f -16
+jgz a -19
diff --git a/2017/day-18/solution.lua b/2017/day-18/solution.lua
new file mode 100755
index 0000000..8ee8b90
--- /dev/null
+++ b/2017/day-18/solution.lua
@@ -0,0 +1,160 @@
+#!/usr/bin/env lua
+
+function split(input, match)
+	-- Stolen from stack overflow.
+	-- Why doesn't lua have string split?
+	local i = 1; t = {}
+
+	for str in string.gmatch(input, match) do
+		t[i] = str
+		i = i + 1
+	end
+
+	return t
+end
+
+instructions = {}
+icount = 0
+
+while true do
+	line = io.read()
+
+	if line == nil then break end
+
+	instructions[icount] = split(line, "%S+")
+	icount = icount + 1
+end
+
+registers = {}
+
+function argval(input)
+	if tonumber(input) ~= nil then
+		return tonumber(input)
+	elseif registers[input] ~= nil then
+		return registers[input]
+	else
+		return 0
+	end
+end
+
+iptr = 0
+
+while true do
+	instr = instructions[iptr]
+
+	if instr[1] == "set" then
+		registers[instr[2]] = argval(instr[3])
+	elseif instr[1] == "snd" then
+		last_played = argval(instr[2])
+	elseif instr[1] == "add" then
+		registers[instr[2]] = argval(instr[2]) + argval(instr[3])
+	elseif instr[1] == "mul" then
+		registers[instr[2]] = argval(instr[2]) * argval(instr[3])
+	elseif instr[1] == "mod" then
+		registers[instr[2]] = argval(instr[2]) % argval(instr[3])
+	elseif instr[1] == "rcv" then
+		print("Last played", last_played)
+		break
+	elseif instr[1] == "jgz" then
+		if argval(instr[2]) > 0 then
+			iptr = iptr + argval(instr[3]) - 1 -- correct for the subsequent add
+		end
+	else
+		print("Illegal instruction", instr[1])
+		break
+	end
+
+	iptr = iptr + 1
+end
+
+registers = {}
+registers[0] = {}
+registers[1] = {}
+
+function argval(input, pid)
+	if tonumber(input) ~= nil then
+		return tonumber(input)
+	elseif registers[pid][input] ~= nil then
+		return registers[pid][input]
+	else
+		return pid
+	end
+end
+
+-- Double instruction pointer
+iptr = {}
+iptr[0] = 0
+iptr[1] = 0
+-- Double receive buffer
+rbuf = {}
+rbuf[0] = {}
+rbuf[1] = {}
+-- Pointer in the receive buffer
+rptr = {}
+rptr[0] = 0
+rptr[1] = 0
+-- Number of entries in each buffer
+rctr = {}
+rctr[0] = 0
+rctr[1] = 0
+-- Whether one thread is waiting
+waiting = {}
+waiting[0] = false
+waiting[1] = false
+
+sends = 0
+
+pid = 0
+
+function nextpid(pid)
+	if pid == 0 then
+		return 1
+	else
+		return 0
+	end
+end
+
+while true do
+	instr = instructions[iptr[pid]]
+
+	if waiting[0] and waiting[1] then
+		print("Deadlocked!")
+		break
+	end
+
+	if instr[1] == "set" then
+		registers[pid][instr[2]] = argval(instr[3], pid)
+	elseif instr[1] == "snd" then
+		rbuf[nextpid(pid)][rctr[nextpid(pid)]] = argval(instr[2], pid)
+		rctr[nextpid(pid)] = rctr[nextpid(pid)] + 1
+	elseif instr[1] == "add" then
+		registers[pid][instr[2]] = argval(instr[2], pid) + argval(instr[3], pid)
+	elseif instr[1] == "mul" then
+		registers[pid][instr[2]] = argval(instr[2], pid) * argval(instr[3], pid)
+	elseif instr[1] == "mod" then
+		registers[pid][instr[2]] = argval(instr[2], pid) % argval(instr[3], pid)
+	elseif instr[1] == "rcv" then
+		if rbuf[pid][rptr[pid]] ~= nil then
+			-- Have value, read and continue
+			registers[pid][instr[2]] = rbuf[pid][rptr[pid]]
+			rptr[pid] = rptr[pid] + 1
+			waiting[nextpid(pid)] = false
+		else
+			-- Need to wait for value, continue with execution of the other
+			waiting[pid] = true
+			pid = nextpid(pid)
+			iptr[pid] = iptr[pid] - 1 -- Correct for subsequent increase
+		end
+	elseif instr[1] == "jgz" then
+		if argval(instr[2], pid) > 0 then
+			iptr[pid] = iptr[pid] + argval(instr[3], pid) - 1 -- correct for the subsequent add
+		end
+	else
+		print("Illegal instruction", instr[1])
+		break
+	end
+
+	iptr[pid] = iptr[pid] + 1
+end
+
+print("Final sends from 1:", rctr[0])