From fc5641cb69f77ff83a7265679c26f0c25fc4e2ef Mon Sep 17 00:00:00 2001
From: Christopher Young <cyoung@gmail.com>
Date: Tue, 21 Jun 2016 14:54:59 -0400
Subject: [PATCH] Integrate @toofishes improvement: Unroll loop in
 convert_to_phi.
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“This yields a 10% CPU savings vs the original single value per loop
iteration implementation on a Raspberry Pi 2 Model B.”

https://github.com/mutability/dump978/commit/b0958f4305d2c7355d07fa9b938
8f6ad1b31b161
---
 dump978/dump978.c    | 20 ++++++++++++++++----
 uatparse/uatparse.go | 13 +++++++++----
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/dump978/dump978.c b/dump978/dump978.c
index 1de85ffc..6f61ac72 100644
--- a/dump978/dump978.c
+++ b/dump978/dump978.c
@@ -143,11 +143,23 @@ void make_atan2_table(void) {
   }
 }
 
-static void convert_to_phi(uint16_t *dest, uint16_t *src, int n) {
-  int i;
+static void convert_to_phi(uint16_t *buffer, int n)
+{
+    int i;
 
-  for (i = 0; i < n; ++i)
-    dest[i] = iqphase[src[i]];
+    // unroll the loop. n is always > 2048, usually 36864
+    for (i = 0; i+8 <= n; i += 8) {
+        buffer[i] = iqphase[buffer[i]];
+        buffer[i+1] = iqphase[buffer[i+1]];
+        buffer[i+2] = iqphase[buffer[i+2]];
+        buffer[i+3] = iqphase[buffer[i+3]];
+        buffer[i+4] = iqphase[buffer[i+4]];
+        buffer[i+5] = iqphase[buffer[i+5]];
+        buffer[i+6] = iqphase[buffer[i+6]];
+        buffer[i+7] = iqphase[buffer[i+7]];
+    }
+    for (; i < n; ++i)
+        buffer[i] = iqphase[buffer[i]];
 }
 
 static void calc_power(uint16_t *samples, int len) { // sets signal_strength to scaled amplitude. 0 = no signal, 1000 = saturated receiver on all samples in measurement.
diff --git a/uatparse/uatparse.go b/uatparse/uatparse.go
index c5c11e87..f6bb4fd3 100644
--- a/uatparse/uatparse.go
+++ b/uatparse/uatparse.go
@@ -599,9 +599,14 @@ func New(buf string) (*UATMsg, error) {
 	buf = strings.Trim(buf, "\r\n") // Remove newlines.
 	x := strings.Split(buf, ";")    // We want to discard everything before the first ';'.
 
+	if len(x) < 2 {
+		return ret, errors.New(fmt.Sprintf("New UATMsg: Invalid format (%s).", buf))
+	}
+
 	/*
-		RS_Err         int
-		SignalStrength int
+		Parse _;rs=?;ss=? - if available.
+			RS_Err         int
+			SignalStrength int
 	*/
 	ret.SignalStrength = -1
 	ret.RS_Err = -1
@@ -628,10 +633,10 @@ func New(buf string) (*UATMsg, error) {
 	}
 
 	if s[0] != '+' { // Only want + ("Uplink") messages currently. - (Downlink) or messages that start with other are discarded.
-		return ret, errors.New("New UATMsg: expecting uplink frames.")
+		return ret, errors.New("New UATMsg: expecting uplink frame.")
 	}
 
-	s = s[1:]
+	s = s[1:] // Remove the preceding '+' or '-' character.
 
 	// Convert the hex string into a byte array.
 	frame := make([]byte, UPLINK_FRAME_DATA_BYTES)