From 09e514732788d821189c59ddc58e70355ba1a3cb Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Mon, 23 Sep 2019 20:09:39 +0200
Subject: Add code from common repository

---
 src/fec/decode_rs.h | 298 ----------------------------------------------------
 1 file changed, 298 deletions(-)
 delete mode 100644 src/fec/decode_rs.h

(limited to 'src/fec/decode_rs.h')

diff --git a/src/fec/decode_rs.h b/src/fec/decode_rs.h
deleted file mode 100644
index c165cf3..0000000
--- a/src/fec/decode_rs.h
+++ /dev/null
@@ -1,298 +0,0 @@
-/* The guts of the Reed-Solomon decoder, meant to be #included
- * into a function body with the following typedefs, macros and variables supplied
- * according to the code parameters:
-
- * data_t - a typedef for the data symbol
- * data_t data[] - array of NN data and parity symbols to be corrected in place
- * retval - an integer lvalue into which the decoder's return code is written
- * NROOTS - the number of roots in the RS code generator polynomial,
- *          which is the same as the number of parity symbols in a block.
-            Integer variable or literal.
- * NN - the total number of symbols in a RS block. Integer variable or literal.
- * PAD - the number of pad symbols in a block. Integer variable or literal.
- * ALPHA_TO - The address of an array of NN elements to convert Galois field
- *            elements in index (log) form to polynomial form. Read only.
- * INDEX_OF - The address of an array of NN elements to convert Galois field
- *            elements in polynomial form to index (log) form. Read only.
- * MODNN - a function to reduce its argument modulo NN. May be inline or a macro.
- * FCR - An integer literal or variable specifying the first consecutive root of the
- *       Reed-Solomon generator polynomial. Integer variable or literal.
- * PRIM - The primitive root of the generator poly. Integer variable or literal.
- * DEBUG - If set to 1 or more, do various internal consistency checking. Leave this
- *         undefined for production code
-
- * The memset(), memmove(), and memcpy() functions are used. The appropriate header
- * file declaring these functions (usually <string.h>) must be included by the calling
- * program.
- */
-
-
-#if !defined(NROOTS)
-#error "NROOTS not defined"
-#endif
-
-#if !defined(NN)
-#error "NN not defined"
-#endif
-
-#if !defined(PAD)
-#error "PAD not defined"
-#endif
-
-#if !defined(ALPHA_TO)
-#error "ALPHA_TO not defined"
-#endif
-
-#if !defined(INDEX_OF)
-#error "INDEX_OF not defined"
-#endif
-
-#if !defined(MODNN)
-#error "MODNN not defined"
-#endif
-
-#if !defined(FCR)
-#error "FCR not defined"
-#endif
-
-#if !defined(PRIM)
-#error "PRIM not defined"
-#endif
-
-#if !defined(NULL)
-#define NULL ((void *)0)
-#endif
-
-#undef MIN
-#define	MIN(a,b)	((a) < (b) ? (a) : (b))
-#undef A0
-#define A0 (NN)
-
-{
-  int deg_lambda, el, deg_omega;
-  int i, j, r,k;
-  data_t u,q,tmp,num1,num2,den,discr_r;
-  data_t lambda[NROOTS+1], s[NROOTS];	/* Err+Eras Locator poly
-					 * and syndrome poly */
-  data_t b[NROOTS+1], t[NROOTS+1], omega[NROOTS+1];
-  data_t root[NROOTS], reg[NROOTS+1], loc[NROOTS];
-  int syn_error, count;
-
-  /* form the syndromes; i.e., evaluate data(x) at roots of g(x) */
-  for(i=0;i<NROOTS;i++)
-    s[i] = data[0];
-
-  for(j=1;j<NN-PAD;j++){
-    for(i=0;i<NROOTS;i++){
-      if(s[i] == 0){
-	s[i] = data[j];
-      } else {
-	s[i] = data[j] ^ ALPHA_TO[MODNN(INDEX_OF[s[i]] + (FCR+i)*PRIM)];
-      }
-    }
-  }
-
-  /* Convert syndromes to index form, checking for nonzero condition */
-  syn_error = 0;
-  for(i=0;i<NROOTS;i++){
-    syn_error |= s[i];
-    s[i] = INDEX_OF[s[i]];
-  }
-
-  if (!syn_error) {
-    /* if syndrome is zero, data[] is a codeword and there are no
-     * errors to correct. So return data[] unmodified
-     */
-    count = 0;
-    goto finish;
-  }
-  memset(&lambda[1],0,NROOTS*sizeof(lambda[0]));
-  lambda[0] = 1;
-
-  if (no_eras > 0) {
-    /* Init lambda to be the erasure locator polynomial */
-    lambda[1] = ALPHA_TO[MODNN(PRIM*(NN-1-eras_pos[0]))];
-    for (i = 1; i < no_eras; i++) {
-      u = MODNN(PRIM*(NN-1-eras_pos[i]));
-      for (j = i+1; j > 0; j--) {
-	tmp = INDEX_OF[lambda[j - 1]];
-	if(tmp != A0)
-	  lambda[j] ^= ALPHA_TO[MODNN(u + tmp)];
-      }
-    }
-
-#if DEBUG >= 1
-    /* Test code that verifies the erasure locator polynomial just constructed
-       Needed only for decoder debugging. */
-    
-    /* find roots of the erasure location polynomial */
-    for(i=1;i<=no_eras;i++)
-      reg[i] = INDEX_OF[lambda[i]];
-
-    count = 0;
-    for (i = 1,k=IPRIM-1; i <= NN; i++,k = MODNN(k+IPRIM)) {
-      q = 1;
-      for (j = 1; j <= no_eras; j++)
-	if (reg[j] != A0) {
-	  reg[j] = MODNN(reg[j] + j);
-	  q ^= ALPHA_TO[reg[j]];
-	}
-      if (q != 0)
-	continue;
-      /* store root and error location number indices */
-      root[count] = i;
-      loc[count] = k;
-      count++;
-    }
-    if (count != no_eras) {
-      printf("count = %d no_eras = %d\n lambda(x) is WRONG\n",count,no_eras);
-      count = -1;
-      goto finish;
-    }
-#if DEBUG >= 2
-    printf("\n Erasure positions as determined by roots of Eras Loc Poly:\n");
-    for (i = 0; i < count; i++)
-      printf("%d ", loc[i]);
-    printf("\n");
-#endif
-#endif
-  }
-  for(i=0;i<NROOTS+1;i++)
-    b[i] = INDEX_OF[lambda[i]];
-  
-  /*
-   * Begin Berlekamp-Massey algorithm to determine error+erasure
-   * locator polynomial
-   */
-  r = no_eras;
-  el = no_eras;
-  while (++r <= NROOTS) {	/* r is the step number */
-    /* Compute discrepancy at the r-th step in poly-form */
-    discr_r = 0;
-    for (i = 0; i < r; i++){
-      if ((lambda[i] != 0) && (s[r-i-1] != A0)) {
-	discr_r ^= ALPHA_TO[MODNN(INDEX_OF[lambda[i]] + s[r-i-1])];
-      }
-    }
-    discr_r = INDEX_OF[discr_r];	/* Index form */
-    if (discr_r == A0) {
-      /* 2 lines below: B(x) <-- x*B(x) */
-      memmove(&b[1],b,NROOTS*sizeof(b[0]));
-      b[0] = A0;
-    } else {
-      /* 7 lines below: T(x) <-- lambda(x) - discr_r*x*b(x) */
-      t[0] = lambda[0];
-      for (i = 0 ; i < NROOTS; i++) {
-	if(b[i] != A0)
-	  t[i+1] = lambda[i+1] ^ ALPHA_TO[MODNN(discr_r + b[i])];
-	else
-	  t[i+1] = lambda[i+1];
-      }
-      if (2 * el <= r + no_eras - 1) {
-	el = r + no_eras - el;
-	/*
-	 * 2 lines below: B(x) <-- inv(discr_r) *
-	 * lambda(x)
-	 */
-	for (i = 0; i <= NROOTS; i++)
-	  b[i] = (lambda[i] == 0) ? A0 : MODNN(INDEX_OF[lambda[i]] - discr_r + NN);
-      } else {
-	/* 2 lines below: B(x) <-- x*B(x) */
-	memmove(&b[1],b,NROOTS*sizeof(b[0]));
-	b[0] = A0;
-      }
-      memcpy(lambda,t,(NROOTS+1)*sizeof(t[0]));
-    }
-  }
-
-  /* Convert lambda to index form and compute deg(lambda(x)) */
-  deg_lambda = 0;
-  for(i=0;i<NROOTS+1;i++){
-    lambda[i] = INDEX_OF[lambda[i]];
-    if(lambda[i] != A0)
-      deg_lambda = i;
-  }
-  /* Find roots of the error+erasure locator polynomial by Chien search */
-  memcpy(&reg[1],&lambda[1],NROOTS*sizeof(reg[0]));
-  count = 0;		/* Number of roots of lambda(x) */
-  for (i = 1,k=IPRIM-1; i <= NN; i++,k = MODNN(k+IPRIM)) {
-    q = 1; /* lambda[0] is always 0 */
-    for (j = deg_lambda; j > 0; j--){
-      if (reg[j] != A0) {
-	reg[j] = MODNN(reg[j] + j);
-	q ^= ALPHA_TO[reg[j]];
-      }
-    }
-    if (q != 0)
-      continue; /* Not a root */
-    /* store root (index-form) and error location number */
-#if DEBUG>=2
-    printf("count %d root %d loc %d\n",count,i,k);
-#endif
-    root[count] = i;
-    loc[count] = k;
-    /* If we've already found max possible roots,
-     * abort the search to save time
-     */
-    if(++count == deg_lambda)
-      break;
-  }
-  if (deg_lambda != count) {
-    /*
-     * deg(lambda) unequal to number of roots => uncorrectable
-     * error detected
-     */
-    count = -1;
-    goto finish;
-  }
-  /*
-   * Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo
-   * x**NROOTS). in index form. Also find deg(omega).
-   */
-  deg_omega = deg_lambda-1;
-  for (i = 0; i <= deg_omega;i++){
-    tmp = 0;
-    for(j=i;j >= 0; j--){
-      if ((s[i - j] != A0) && (lambda[j] != A0))
-	tmp ^= ALPHA_TO[MODNN(s[i - j] + lambda[j])];
-    }
-    omega[i] = INDEX_OF[tmp];
-  }
-
-  /*
-   * Compute error values in poly-form. num1 = omega(inv(X(l))), num2 =
-   * inv(X(l))**(FCR-1) and den = lambda_pr(inv(X(l))) all in poly-form
-   */
-  for (j = count-1; j >=0; j--) {
-    num1 = 0;
-    for (i = deg_omega; i >= 0; i--) {
-      if (omega[i] != A0)
-	num1  ^= ALPHA_TO[MODNN(omega[i] + i * root[j])];
-    }
-    num2 = ALPHA_TO[MODNN(root[j] * (FCR - 1) + NN)];
-    den = 0;
-    
-    /* lambda[i+1] for i even is the formal derivative lambda_pr of lambda[i] */
-    for (i = MIN(deg_lambda,NROOTS-1) & ~1; i >= 0; i -=2) {
-      if(lambda[i+1] != A0)
-	den ^= ALPHA_TO[MODNN(lambda[i+1] + i * root[j])];
-    }
-#if DEBUG >= 1
-    if (den == 0) {
-      printf("\n ERROR: denominator = 0\n");
-      count = -1;
-      goto finish;
-    }
-#endif
-    /* Apply error to data */
-    if (num1 != 0 && loc[j] >= PAD) {
-      data[loc[j]-PAD] ^= ALPHA_TO[MODNN(INDEX_OF[num1] + INDEX_OF[num2] + NN - INDEX_OF[den])];
-    }
-  }
- finish:
-  if(eras_pos != NULL){
-    for(i=0;i<count;i++)
-      eras_pos[i] = loc[i];
-  }
-  retval = count;
-}
-- 
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