From e3f834f26170cfd67ad0804e56e1044fca8e26bd Mon Sep 17 00:00:00 2001
From: Justin Brzozoski <justin.brzozoski@gmail.com>
Date: Tue, 9 Jun 2020 22:51:59 -0400
Subject: [PATCH] Small improvement of FX.25 RS encoder speed

The old design walked the entire feedback array XORing all values, then
shifted them all down by one index. This design does the shift-by-one
while doing the XOR work to save a step.

Signed-off-by: Justin Brzozoski <justin.brzozoski@gmail.com>
---
 src/fx25_encode.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/fx25_encode.c b/src/fx25_encode.c
index 02c20a84..7575444d 100644
--- a/src/fx25_encode.c
+++ b/src/fx25_encode.c
@@ -69,15 +69,15 @@ void ENCODE_RS(struct rs * restrict rs, DTYPE * restrict data, DTYPE * restrict
   for(i=0;i<NN-NROOTS;i++){
     feedback = INDEX_OF[data[i] ^ bb[0]];
     if(feedback != A0){      /* feedback term is non-zero */
+      /* Shift and XOR */
       for(j=1;j<NROOTS;j++)
-	    bb[j] ^= ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS-j])];
-    }
-    /* Shift */
-    memmove(&bb[0],&bb[1],sizeof(DTYPE)*(NROOTS-1));
-    if(feedback != A0)
+	    bb[j-1] = bb[j] ^ ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS-j])];
       bb[NROOTS-1] = ALPHA_TO[MODNN(feedback + GENPOLY[0])];
-    else
+    } else{
+      /* Shift only */
+      memmove(&bb[0],&bb[1],sizeof(DTYPE)*(NROOTS-1));
       bb[NROOTS-1] = 0;
+    }
   }
 }