From e12e9eaac8c3851770b09de7d2f398565f180940 Mon Sep 17 00:00:00 2001
From: Ken Shirriff <web1@righto.com>
Date: Fri, 22 Jan 2010 23:26:54 -0800
Subject: [PATCH] Add "hash encoding" to generate a value for unknown
 encodings. For an unknown encoding, an arbitrary 32-bit value will be
 generated.

---
 IRremote.cpp                       | 63 +++++++++++++++++++++++++++---
 IRremote.h                         |  3 ++
 examples/IRrecvDump/IRrecvDump.pde | 34 ++++++++--------
 3 files changed, 77 insertions(+), 23 deletions(-)

diff --git a/IRremote.cpp b/IRremote.cpp
index bb6083e..236737d 100644
--- a/IRremote.cpp
+++ b/IRremote.cpp
@@ -368,11 +368,10 @@ int IRrecv::decode(decode_results *results) {
   if (decodeRC6(results)) {
     return DECODED;
   }
-  if (results->rawlen >= 6) {
-    // Only return raw buffer if at least 6 bits
-    results->decode_type = UNKNOWN;
-    results->bits = 0;
-    results->value = 0;
+  // decodeHash returns a hash on any input.
+  // Thus, it needs to be last in the list.
+  // If you add any decodes, add them before this.
+  if (decodeHash(results)) {
     return DECODED;
   }
   // Throw away and start over
@@ -599,3 +598,57 @@ long IRrecv::decodeRC6(decode_results *results) {
   results->decode_type = RC6;
   return DECODED;
 }
+
+/* -----------------------------------------------------------------------
+ * hashdecode - decode an arbitrary IR code.
+ * Instead of decoding using a standard encoding scheme
+ * (e.g. Sony, NEC, RC5), the code is hashed to a 32-bit value.
+ *
+ * The algorithm: look at the sequence of MARK signals, and see if each one
+ * is shorter (0), the same length (1), or longer (2) than the previous.
+ * Do the same with the SPACE signals.  Hszh the resulting sequence of 0's,
+ * 1's, and 2's to a 32-bit value.  This will give a unique value for each
+ * different code (probably), for most code systems.
+ *
+ * http://arcfn.com/2010/01/using-arbitrary-remotes-with-arduino.html
+ */
+
+// Compare two tick values, returning 0 if newval is shorter,
+// 1 if newval is equal, and 2 if newval is longer
+// Use a tolerance of 20%
+int IRrecv::compare(unsigned int oldval, unsigned int newval) {
+  if (newval < oldval * .8) {
+    return 0;
+  } 
+  else if (oldval < newval * .8) {
+    return 2;
+  } 
+  else {
+    return 1;
+  }
+}
+
+// Use FNV hash algorithm: http://isthe.com/chongo/tech/comp/fnv/#FNV-param
+#define FNV_PRIME_32 16777619
+#define FNV_BASIS_32 2166136261
+
+/* Converts the raw code values into a 32-bit hash code.
+ * Hopefully this code is unique for each button.
+ * This isn't a "real" decoding, just an arbitrary value.
+ */
+long IRrecv::decodeHash(decode_results *results) {
+  // Require at least 6 samples to prevent triggering on noise
+  if (results->rawlen < 6) {
+    return ERR;
+  }
+  long hash = FNV_BASIS_32;
+  for (int i = 1; i+2 < results->rawlen; i++) {
+    int value =  compare(results->rawbuf[i], results->rawbuf[i+2]);
+    // Add value into the hash
+    hash = (hash * FNV_PRIME_32) ^ value;
+  }
+  results->value = hash;
+  results->bits = 32;
+  results->decode_type = UNKNOWN;
+  return DECODED;
+}
diff --git a/IRremote.h b/IRremote.h
index 35fb445..f5e7a7b 100644
--- a/IRremote.h
+++ b/IRremote.h
@@ -56,6 +56,9 @@ private:
   long decodeSony(decode_results *results);
   long decodeRC5(decode_results *results);
   long decodeRC6(decode_results *results);
+  long decodeHash(decode_results *results);
+  int compare(unsigned int oldval, unsigned int newval);
+
 } 
 ;
 
diff --git a/examples/IRrecvDump/IRrecvDump.pde b/examples/IRrecvDump/IRrecvDump.pde
index ad3c599..93495b7 100644
--- a/examples/IRrecvDump/IRrecvDump.pde
+++ b/examples/IRrecvDump/IRrecvDump.pde
@@ -28,26 +28,24 @@ void setup()
 void dump(decode_results *results) {
   int count = results->rawlen;
   if (results->decode_type == UNKNOWN) {
-    Serial.println("Could not decode message");
+    Serial.print("Unknown encoding: ");
   } 
-  else {
-    if (results->decode_type == NEC) {
-      Serial.print("Decoded NEC: ");
-    } 
-    else if (results->decode_type == SONY) {
-      Serial.print("Decoded SONY: ");
-    } 
-    else if (results->decode_type == RC5) {
-      Serial.print("Decoded RC5: ");
-    } 
-    else if (results->decode_type == RC6) {
-      Serial.print("Decoded RC6: ");
-    }
-    Serial.print(results->value, HEX);
-    Serial.print(" (");
-    Serial.print(results->bits, DEC);
-    Serial.println(" bits)");
+  else if (results->decode_type == NEC) {
+    Serial.print("Decoded NEC: ");
+  } 
+  else if (results->decode_type == SONY) {
+    Serial.print("Decoded SONY: ");
+  } 
+  else if (results->decode_type == RC5) {
+    Serial.print("Decoded RC5: ");
+  } 
+  else if (results->decode_type == RC6) {
+    Serial.print("Decoded RC6: ");
   }
+  Serial.print(results->value, HEX);
+  Serial.print(" (");
+  Serial.print(results->bits, DEC);
+  Serial.println(" bits)");
   Serial.print("Raw (");
   Serial.print(count, DEC);
   Serial.print("): ");