From fd6d695275f88e83ebba6fa39afc044e329a690f Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Sun, 25 Dec 2016 23:53:51 +0100
Subject: Add first version of EDI input

---
 lib/fec/init_rs.h | 104 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 lib/fec/init_rs.h

(limited to 'lib/fec/init_rs.h')

diff --git a/lib/fec/init_rs.h b/lib/fec/init_rs.h
new file mode 100644
index 0000000..a5e8b4a
--- /dev/null
+++ b/lib/fec/init_rs.h
@@ -0,0 +1,104 @@
+/* Common code for intializing a Reed-Solomon control block (char or int symbols)
+ * Copyright 2004 Phil Karn, KA9Q
+ * May be used under the terms of the GNU Lesser General Public License (LGPL)
+ */
+
+{
+  int i, j, sr,root,iprim;
+
+  rs = NULL;
+  /* Check parameter ranges */
+  if(symsize < 0 || symsize > 8*sizeof(data_t)){
+    goto done;
+  }
+
+  if(fcr < 0 || fcr >= (1<<symsize))
+    goto done;
+  if(prim <= 0 || prim >= (1<<symsize))
+    goto done;
+  if(nroots < 0 || nroots >= (1<<symsize))
+    goto done; /* Can't have more roots than symbol values! */
+  if(pad < 0 || pad >= ((1<<symsize) -1 - nroots))
+    goto done; /* Too much padding */
+
+  rs = (struct rs *)calloc(1,sizeof(struct rs));
+  if(rs == NULL)
+    goto done;
+
+  rs->mm = symsize;
+  rs->nn = (1<<symsize)-1;
+  rs->pad = pad;
+
+  rs->alpha_to = (data_t *)malloc(sizeof(data_t)*(rs->nn+1));
+  if(rs->alpha_to == NULL){
+    free(rs);
+    rs = NULL;
+    goto done;
+  }
+  rs->index_of = (data_t *)malloc(sizeof(data_t)*(rs->nn+1));
+  if(rs->index_of == NULL){
+    free(rs->alpha_to);
+    free(rs);
+    rs = NULL;
+    goto done;
+  }
+
+  /* Generate Galois field lookup tables */
+  rs->index_of[0] = A0; /* log(zero) = -inf */
+  rs->alpha_to[A0] = 0; /* alpha**-inf = 0 */
+  sr = 1;
+  for(i=0;i<rs->nn;i++){
+    rs->index_of[sr] = i;
+    rs->alpha_to[i] = sr;
+    sr <<= 1;
+    if(sr & (1<<symsize))
+      sr ^= gfpoly;
+    sr &= rs->nn;
+  }
+  if(sr != 1){
+    /* field generator polynomial is not primitive! */
+    free(rs->alpha_to);
+    free(rs->index_of);
+    free(rs);
+    rs = NULL;
+    goto done;
+  }
+
+  /* Form RS code generator polynomial from its roots */
+  rs->genpoly = (data_t *)malloc(sizeof(data_t)*(nroots+1));
+  if(rs->genpoly == NULL){
+    free(rs->alpha_to);
+    free(rs->index_of);
+    free(rs);
+    rs = NULL;
+    goto done;
+  }
+  rs->fcr = fcr;
+  rs->prim = prim;
+  rs->nroots = nroots;
+
+  /* Find prim-th root of 1, used in decoding */
+  for(iprim=1;(iprim % prim) != 0;iprim += rs->nn)
+    ;
+  rs->iprim = iprim / prim;
+
+  rs->genpoly[0] = 1;
+  for (i = 0,root=fcr*prim; i < nroots; i++,root += prim) {
+    rs->genpoly[i+1] = 1;
+
+    /* Multiply rs->genpoly[] by  @**(root + x) */
+    for (j = i; j > 0; j--){
+      if (rs->genpoly[j] != 0)
+	rs->genpoly[j] = rs->genpoly[j-1] ^ rs->alpha_to[modnn(rs,rs->index_of[rs->genpoly[j]] + root)];
+      else
+	rs->genpoly[j] = rs->genpoly[j-1];
+    }
+    /* rs->genpoly[0] can never be zero */
+    rs->genpoly[0] = rs->alpha_to[modnn(rs,rs->index_of[rs->genpoly[0]] + root)];
+  }
+  /* convert rs->genpoly[] to index form for quicker encoding */
+  for (i = 0; i <= nroots; i++)
+    rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
+ done:;
+
+}
-- 
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