From 61e836afcf4a843e723b683d9705fa9238fbb4aa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani.haverinen@gmail.com>
Date: Tue, 22 May 2018 00:18:05 +0300
Subject: [PATCH] Add the first optimization pass

---
 README.md |  3 +++
 gir.js    | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/README.md b/README.md
index da3757f..8bd5e48 100644
--- a/README.md
+++ b/README.md
@@ -11,3 +11,6 @@ Everything in the repo is under Unlicense / CC0.
 Status
 ------
 Gir can parse and prettyprint to Javascript console programs in brainfuck.
+Gir supports following optimizations:
+
+* Turn runs or +- or <> into one command
diff --git a/gir.js b/gir.js
index 7c24ac1..a755267 100644
--- a/gir.js
+++ b/gir.js
@@ -1,5 +1,9 @@
 'use strict';
 
+// ------------------------------------------------------------------
+// Definitions
+// ------------------------------------------------------------------
+
 // Use symbols for the names of the instructions
 // Unsure if this helps in any way over strings, but I feel it neater
 
@@ -16,6 +20,10 @@ const loop = Symbol('loop');
 
 // TODO: Add extensions from Eldis
 
+// ------------------------------------------------------------------
+// Parsing
+// ------------------------------------------------------------------
+
 class ParsingError extends Error {}
 
 // (string) → [commandObjects]
@@ -162,3 +170,55 @@ function prettyPrint(parsed) {
 	}
 	printIndented(parsed);
 }
+
+// ------------------------------------------------------------------
+// Optimization passes
+// ------------------------------------------------------------------
+
+// ([commandObjects]) → [commandObjects]
+function joinAdjacentOps(parsed) {
+	// ([commandObjects], commandType) → [commandObjects]
+	function worker(parsed, type) {
+		let optimized = [];
+
+		let prevOfType = false, value = 0;
+		for(let command of parsed) {
+			if(prevOfType && command.type == type) {
+				// Update value, don't add to optimized yet
+				value += command.value;
+			} else if(!prevOfType && command.type == type) {
+				// Start of a possible run of commands
+				prevOfType = true;
+				value = command.value;
+			} else if(prevOfType && command.type != type) {
+				// A run has ended, add it to optimized
+				// However, skip it if value is 0
+				if(value != 0) {
+					optimized.push({type: type, value: value});
+				}
+				// Also add the command for this round
+				optimized.push(command);
+				prevOfType = false;
+			} else {
+				optimized.push(command);
+				prevOfType = false;
+			}
+		}
+		// Did we end with a command of given type
+		if(prevOfType) {
+			// Yes, add it to optimized (unless value is 0)
+			if(value != 0) {
+				optimized.push({type: type, value: value});
+			}
+		}
+
+		return optimized;
+	}
+
+	return worker(worker(parsed, moveHead), add);
+}
+
+// ([commandObjects]) → [commandObjects]
+function optimize(parsed) {
+	return joinAdjacentOps(parsed);
+}