[hamradio-commits] [dump1090] 93/389: Speed up Squawk Decode

[Matthew Ernisse]

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mernisse-guest pushed a commit to branch master
in repository dump1090.

commit 96afd52cb072431a084f4bd14f3f32abf68a28e2
Author: Malcolm Robb <Support at ATTAvionics.com>
Date:   Mon Apr 15 22:12:40 2013 +0100

    Speed up Squawk Decode
    
    Re-write to avoid multiple reads of the same memory variable.
---
 dump1090.c | 35 ++++++++++++++++++++---------------
 1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/dump1090.c b/dump1090.c
index 1b2138c..b89c743 100644
--- a/dump1090.c
+++ b/dump1090.c
@@ -1112,21 +1112,26 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
      *
      * For more info: http://en.wikipedia.org/wiki/Gillham_code */
     {
-        int a,b,c,d;
-
-        a = ((msg[3] & 0x80) >> 5) |
-            ((msg[2] & 0x02) >> 0) |
-            ((msg[2] & 0x08) >> 3);
-        b = ((msg[3] & 0x02) << 1) |
-            ((msg[3] & 0x08) >> 2) |
-            ((msg[3] & 0x20) >> 5);
-        c = ((msg[2] & 0x01) << 2) |
-            ((msg[2] & 0x04) >> 1) |
-            ((msg[2] & 0x10) >> 4);
-        d = ((msg[3] & 0x01) << 2) |
-            ((msg[3] & 0x04) >> 1) |
-            ((msg[3] & 0x10) >> 4);
-        mm->identity = a*1000 + b*100 + c*10 + d;
+        int           decIdentity = 0;
+        unsigned char rawIdentity;
+
+        rawIdentity = msg[2];
+        if (rawIdentity & 0x01) {decIdentity +=   40;} // C4
+        if (rawIdentity & 0x02) {decIdentity += 2000;} // A2
+        if (rawIdentity & 0x04) {decIdentity +=   20;} // C2
+        if (rawIdentity & 0x08) {decIdentity += 1000;} // A1
+        if (rawIdentity & 0x10) {decIdentity +=   10;} // C1
+
+        rawIdentity = msg[3];
+        if (rawIdentity & 0x01) {decIdentity +=    4;} // D4
+        if (rawIdentity & 0x02) {decIdentity +=  400;} // B4
+        if (rawIdentity & 0x04) {decIdentity +=    2;} // D2
+        if (rawIdentity & 0x08) {decIdentity +=  200;} // B2
+        if (rawIdentity & 0x10) {decIdentity +=    1;} // D1
+        if (rawIdentity & 0x20) {decIdentity +=  100;} // B1 
+        if (rawIdentity & 0x80) {decIdentity += 4000;} // A4
+
+        mm->identity = decIdentity;
     }
 
     /* DF 11 & 17: try to populate our ICAO addresses whitelist.

-- 
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