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authorMatthias P. Braendli <matthias.braendli@mpb.li>2018-02-09 10:06:34 +0100
committerMatthias P. Braendli <matthias.braendli@mpb.li>2018-02-09 10:06:34 +0100
commitd10839ab23b4ac4dea5ba183c451b650dd07331a (patch)
tree5f78e10a89134a2a167315a42bc21c5cc3a3cdbb /lib/fec/init_rs.h
parentd1b74c21d8c6f816179cd700dd5859f51bf01d88 (diff)
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Move external code to lib and stop using SUBDIRS
Diffstat (limited to 'lib/fec/init_rs.h')
-rw-r--r--lib/fec/init_rs.h106
1 files changed, 106 insertions, 0 deletions
diff --git a/lib/fec/init_rs.h b/lib/fec/init_rs.h
new file mode 100644
index 0000000..2b2ae98
--- /dev/null
+++ b/lib/fec/init_rs.h
@@ -0,0 +1,106 @@
+/* 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)
+ */
+#undef NULL
+#define NULL ((void *)0)
+
+{
+ 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:;
+
+}