| /* |
| * The copyright in this software is being made available under the 2-clauses |
| * BSD License, included below. This software may be subject to other third |
| * party and contributor rights, including patent rights, and no such rights |
| * are granted under this license. |
| * |
| * Copyright (c) 2001-2003, David Janssens |
| * Copyright (c) 2002-2003, Yannick Verschueren |
| * Copyright (c) 2003-2005, Francois Devaux and Antonin Descampe |
| * Copyright (c) 2005, Herve Drolon, FreeImage Team |
| * Copyright (c) 2002-2005, Communications and remote sensing Laboratory, Universite catholique de Louvain, Belgium |
| * Copyright (c) 2005-2006, Dept. of Electronic and Information Engineering, Universita' degli Studi di Perugia, Italy |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS `AS IS' |
| * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE |
| * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| * POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| #ifdef USE_JPWL |
| |
| /** |
| @file rs.c |
| @brief Functions used to compute the Reed-Solomon parity and check of byte arrays |
| |
| */ |
| |
| /** |
| * Reed-Solomon coding and decoding |
| * Phil Karn ([email protected]) September 1996 |
| * |
| * This file is derived from the program "new_rs_erasures.c" by Robert |
| * Morelos-Zaragoza ([email protected]) and Hari Thirumoorthy |
| * ([email protected]), Aug 1995 |
| * |
| * I've made changes to improve performance, clean up the code and make it |
| * easier to follow. Data is now passed to the encoding and decoding functions |
| * through arguments rather than in global arrays. The decode function returns |
| * the number of corrected symbols, or -1 if the word is uncorrectable. |
| * |
| * This code supports a symbol size from 2 bits up to 16 bits, |
| * implying a block size of 3 2-bit symbols (6 bits) up to 65535 |
| * 16-bit symbols (1,048,560 bits). The code parameters are set in rs.h. |
| * |
| * Note that if symbols larger than 8 bits are used, the type of each |
| * data array element switches from unsigned char to unsigned int. The |
| * caller must ensure that elements larger than the symbol range are |
| * not passed to the encoder or decoder. |
| * |
| */ |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include "rs.h" |
| |
| /* This defines the type used to store an element of the Galois Field |
| * used by the code. Make sure this is something larger than a char if |
| * if anything larger than GF(256) is used. |
| * |
| * Note: unsigned char will work up to GF(256) but int seems to run |
| * faster on the Pentium. |
| */ |
| typedef int gf; |
| |
| /* KK = number of information symbols */ |
| static int KK; |
| |
| /* Primitive polynomials - see Lin & Costello, Appendix A, |
| * and Lee & Messerschmitt, p. 453. |
| */ |
| #if(MM == 2)/* Admittedly silly */ |
| int Pp[MM+1] = { 1, 1, 1 }; |
| |
| #elif(MM == 3) |
| /* 1 + x + x^3 */ |
| int Pp[MM+1] = { 1, 1, 0, 1 }; |
| |
| #elif(MM == 4) |
| /* 1 + x + x^4 */ |
| int Pp[MM+1] = { 1, 1, 0, 0, 1 }; |
| |
| #elif(MM == 5) |
| /* 1 + x^2 + x^5 */ |
| int Pp[MM+1] = { 1, 0, 1, 0, 0, 1 }; |
| |
| #elif(MM == 6) |
| /* 1 + x + x^6 */ |
| int Pp[MM+1] = { 1, 1, 0, 0, 0, 0, 1 }; |
| |
| #elif(MM == 7) |
| /* 1 + x^3 + x^7 */ |
| int Pp[MM+1] = { 1, 0, 0, 1, 0, 0, 0, 1 }; |
| |
| #elif(MM == 8) |
| /* 1+x^2+x^3+x^4+x^8 */ |
| int Pp[MM+1] = { 1, 0, 1, 1, 1, 0, 0, 0, 1 }; |
| |
| #elif(MM == 9) |
| /* 1+x^4+x^9 */ |
| int Pp[MM+1] = { 1, 0, 0, 0, 1, 0, 0, 0, 0, 1 }; |
| |
| #elif(MM == 10) |
| /* 1+x^3+x^10 */ |
| int Pp[MM+1] = { 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1 }; |
| |
| #elif(MM == 11) |
| /* 1+x^2+x^11 */ |
| int Pp[MM+1] = { 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1 }; |
| |
| #elif(MM == 12) |
| /* 1+x+x^4+x^6+x^12 */ |
| int Pp[MM+1] = { 1, 1, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1 }; |
| |
| #elif(MM == 13) |
| /* 1+x+x^3+x^4+x^13 */ |
| int Pp[MM+1] = { 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1 }; |
| |
| #elif(MM == 14) |
| /* 1+x+x^6+x^10+x^14 */ |
| int Pp[MM+1] = { 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1 }; |
| |
| #elif(MM == 15) |
| /* 1+x+x^15 */ |
| int Pp[MM+1] = { 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }; |
| |
| #elif(MM == 16) |
| /* 1+x+x^3+x^12+x^16 */ |
| int Pp[MM+1] = { 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1 }; |
| |
| #else |
| #error "MM must be in range 2-16" |
| #endif |
| |
| /* Alpha exponent for the first root of the generator polynomial */ |
| #define B0 0 /* Different from the default 1 */ |
| |
| /* index->polynomial form conversion table */ |
| gf Alpha_to[NN + 1]; |
| |
| /* Polynomial->index form conversion table */ |
| gf Index_of[NN + 1]; |
| |
| /* No legal value in index form represents zero, so |
| * we need a special value for this purpose |
| */ |
| #define A0 (NN) |
| |
| /* Generator polynomial g(x) |
| * Degree of g(x) = 2*TT |
| * has roots @**B0, @**(B0+1), ... ,@^(B0+2*TT-1) |
| */ |
| /*gf Gg[NN - KK + 1];*/ |
| gf Gg[NN - 1]; |
| |
| /* Compute x % NN, where NN is 2**MM - 1, |
| * without a slow divide |
| */ |
| static /*inline*/ gf |
| modnn(int x) |
| { |
| while (x >= NN) { |
| x -= NN; |
| x = (x >> MM) + (x & NN); |
| } |
| return x; |
| } |
| |
| /*#define min(a,b) ((a) < (b) ? (a) : (b))*/ |
| |
| #define CLEAR(a,n) {\ |
| int ci;\ |
| for(ci=(n)-1;ci >=0;ci--)\ |
| (a)[ci] = 0;\ |
| } |
| |
| #define COPY(a,b,n) {\ |
| int ci;\ |
| for(ci=(n)-1;ci >=0;ci--)\ |
| (a)[ci] = (b)[ci];\ |
| } |
| #define COPYDOWN(a,b,n) {\ |
| int ci;\ |
| for(ci=(n)-1;ci >=0;ci--)\ |
| (a)[ci] = (b)[ci];\ |
| } |
| |
| void init_rs(int k) |
| { |
| KK = k; |
| if (KK >= NN) { |
| printf("KK must be less than 2**MM - 1\n"); |
| exit(1); |
| } |
| |
| generate_gf(); |
| gen_poly(); |
| } |
| |
| /* generate GF(2**m) from the irreducible polynomial p(X) in p[0]..p[m] |
| lookup tables: index->polynomial form alpha_to[] contains j=alpha**i; |
| polynomial form -> index form index_of[j=alpha**i] = i |
| alpha=2 is the primitive element of GF(2**m) |
| HARI's COMMENT: (4/13/94) alpha_to[] can be used as follows: |
| Let @ represent the primitive element commonly called "alpha" that |
| is the root of the primitive polynomial p(x). Then in GF(2^m), for any |
| 0 <= i <= 2^m-2, |
| @^i = a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1) |
| where the binary vector (a(0),a(1),a(2),...,a(m-1)) is the representation |
| of the integer "alpha_to[i]" with a(0) being the LSB and a(m-1) the MSB. Thus for |
| example the polynomial representation of @^5 would be given by the binary |
| representation of the integer "alpha_to[5]". |
| Similarly, index_of[] can be used as follows: |
| As above, let @ represent the primitive element of GF(2^m) that is |
| the root of the primitive polynomial p(x). In order to find the power |
| of @ (alpha) that has the polynomial representation |
| a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1) |
| we consider the integer "i" whose binary representation with a(0) being LSB |
| and a(m-1) MSB is (a(0),a(1),...,a(m-1)) and locate the entry |
| "index_of[i]". Now, @^index_of[i] is that element whose polynomial |
| representation is (a(0),a(1),a(2),...,a(m-1)). |
| NOTE: |
| The element alpha_to[2^m-1] = 0 always signifying that the |
| representation of "@^infinity" = 0 is (0,0,0,...,0). |
| Similarly, the element index_of[0] = A0 always signifying |
| that the power of alpha which has the polynomial representation |
| (0,0,...,0) is "infinity". |
| |
| */ |
| |
| void |
| generate_gf(void) |
| { |
| register int i, mask; |
| |
| mask = 1; |
| Alpha_to[MM] = 0; |
| for (i = 0; i < MM; i++) { |
| Alpha_to[i] = mask; |
| Index_of[Alpha_to[i]] = i; |
| /* If Pp[i] == 1 then, term @^i occurs in poly-repr of @^MM */ |
| if (Pp[i] != 0) |
| Alpha_to[MM] ^= mask; /* Bit-wise EXOR operation */ |
| mask <<= 1; /* single left-shift */ |
| } |
| Index_of[Alpha_to[MM]] = MM; |
| /* |
| * Have obtained poly-repr of @^MM. Poly-repr of @^(i+1) is given by |
| * poly-repr of @^i shifted left one-bit and accounting for any @^MM |
| * term that may occur when poly-repr of @^i is shifted. |
| */ |
| mask >>= 1; |
| for (i = MM + 1; i < NN; i++) { |
| if (Alpha_to[i - 1] >= mask) |
| Alpha_to[i] = Alpha_to[MM] ^ ((Alpha_to[i - 1] ^ mask) << 1); |
| else |
| Alpha_to[i] = Alpha_to[i - 1] << 1; |
| Index_of[Alpha_to[i]] = i; |
| } |
| Index_of[0] = A0; |
| Alpha_to[NN] = 0; |
| } |
| |
| |
| /* |
| * Obtain the generator polynomial of the TT-error correcting, length |
| * NN=(2**MM -1) Reed Solomon code from the product of (X+@**(B0+i)), i = 0, |
| * ... ,(2*TT-1) |
| * |
| * Examples: |
| * |
| * If B0 = 1, TT = 1. deg(g(x)) = 2*TT = 2. |
| * g(x) = (x+@) (x+@**2) |
| * |
| * If B0 = 0, TT = 2. deg(g(x)) = 2*TT = 4. |
| * g(x) = (x+1) (x+@) (x+@**2) (x+@**3) |
| */ |
| void |
| gen_poly(void) |
| { |
| register int i, j; |
| |
| Gg[0] = Alpha_to[B0]; |
| Gg[1] = 1; /* g(x) = (X+@**B0) initially */ |
| for (i = 2; i <= NN - KK; i++) { |
| Gg[i] = 1; |
| /* |
| * Below multiply (Gg[0]+Gg[1]*x + ... +Gg[i]x^i) by |
| * (@**(B0+i-1) + x) |
| */ |
| for (j = i - 1; j > 0; j--) |
| if (Gg[j] != 0) |
| Gg[j] = Gg[j - 1] ^ Alpha_to[modnn((Index_of[Gg[j]]) + B0 + i - 1)]; |
| else |
| Gg[j] = Gg[j - 1]; |
| /* Gg[0] can never be zero */ |
| Gg[0] = Alpha_to[modnn((Index_of[Gg[0]]) + B0 + i - 1)]; |
| } |
| /* convert Gg[] to index form for quicker encoding */ |
| for (i = 0; i <= NN - KK; i++) |
| Gg[i] = Index_of[Gg[i]]; |
| } |
| |
| |
| /* |
| * take the string of symbols in data[i], i=0..(k-1) and encode |
| * systematically to produce NN-KK parity symbols in bb[0]..bb[NN-KK-1] data[] |
| * is input and bb[] is output in polynomial form. Encoding is done by using |
| * a feedback shift register with appropriate connections specified by the |
| * elements of Gg[], which was generated above. Codeword is c(X) = |
| * data(X)*X**(NN-KK)+ b(X) |
| */ |
| int |
| encode_rs(dtype *data, dtype *bb) |
| { |
| register int i, j; |
| gf feedback; |
| |
| CLEAR(bb,NN-KK); |
| for (i = KK - 1; i >= 0; i--) { |
| #if (MM != 8) |
| if(data[i] > NN) |
| return -1; /* Illegal symbol */ |
| #endif |
| feedback = Index_of[data[i] ^ bb[NN - KK - 1]]; |
| if (feedback != A0) { /* feedback term is non-zero */ |
| for (j = NN - KK - 1; j > 0; j--) |
| if (Gg[j] != A0) |
| bb[j] = bb[j - 1] ^ Alpha_to[modnn(Gg[j] + feedback)]; |
| else |
| bb[j] = bb[j - 1]; |
| bb[0] = Alpha_to[modnn(Gg[0] + feedback)]; |
| } else { |
| /* feedback term is zero. encoder becomes a |
| * single-byte shifter */ |
| for (j = NN - KK - 1; j > 0; j--) |
| bb[j] = bb[j - 1]; |
| bb[0] = 0; |
| } |
| } |
| return 0; |
| } |
| |
| /* |
| * Performs ERRORS+ERASURES decoding of RS codes. If decoding is successful, |
| * writes the codeword into data[] itself. Otherwise data[] is unaltered. |
| * |
| * Return number of symbols corrected, or -1 if codeword is illegal |
| * or uncorrectable. |
| * |
| * First "no_eras" erasures are declared by the calling program. Then, the |
| * maximum # of errors correctable is t_after_eras = floor((NN-KK-no_eras)/2). |
| * If the number of channel errors is not greater than "t_after_eras" the |
| * transmitted codeword will be recovered. Details of algorithm can be found |
| * in R. Blahut's "Theory ... of Error-Correcting Codes". |
| */ |
| int |
| eras_dec_rs(dtype *data, int *eras_pos, int no_eras) |
| { |
| int deg_lambda, el, deg_omega; |
| int i, j, r; |
| gf u,q,tmp,num1,num2,den,discr_r; |
| gf recd[NN]; |
| /* Err+Eras Locator poly and syndrome poly */ |
| /*gf lambda[NN-KK + 1], s[NN-KK + 1]; |
| gf b[NN-KK + 1], t[NN-KK + 1], omega[NN-KK + 1]; |
| gf root[NN-KK], reg[NN-KK + 1], loc[NN-KK];*/ |
| gf lambda[NN + 1], s[NN + 1]; |
| gf b[NN + 1], t[NN + 1], omega[NN + 1]; |
| gf root[NN], reg[NN + 1], loc[NN]; |
| int syn_error, count; |
| |
| /* data[] is in polynomial form, copy and convert to index form */ |
| for (i = NN-1; i >= 0; i--) { |
| #if (MM != 8) |
| if(data[i] > NN) |
| return -1; /* Illegal symbol */ |
| #endif |
| recd[i] = Index_of[data[i]]; |
| } |
| /* first form the syndromes; i.e., evaluate recd(x) at roots of g(x) |
| * namely @**(B0+i), i = 0, ... ,(NN-KK-1) |
| */ |
| syn_error = 0; |
| for (i = 1; i <= NN-KK; i++) { |
| tmp = 0; |
| for (j = 0; j < NN; j++) |
| if (recd[j] != A0) /* recd[j] in index form */ |
| tmp ^= Alpha_to[modnn(recd[j] + (B0+i-1)*j)]; |
| syn_error |= tmp; /* set flag if non-zero syndrome => |
| * error */ |
| /* store syndrome in index form */ |
| s[i] = Index_of[tmp]; |
| } |
| if (!syn_error) { |
| /* |
| * if syndrome is zero, data[] is a codeword and there are no |
| * errors to correct. So return data[] unmodified |
| */ |
| return 0; |
| } |
| CLEAR(&lambda[1],NN-KK); |
| lambda[0] = 1; |
| if (no_eras > 0) { |
| /* Init lambda to be the erasure locator polynomial */ |
| lambda[1] = Alpha_to[eras_pos[0]]; |
| for (i = 1; i < no_eras; i++) { |
| u = 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)]; |
| } |
| } |
| #ifdef ERASURE_DEBUG |
| /* 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; i <= NN; i++) { |
| 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) { |
| /* store root and error location |
| * number indices |
| */ |
| root[count] = i; |
| loc[count] = NN - i; |
| count++; |
| } |
| } |
| if (count != no_eras) { |
| printf("\n lambda(x) is WRONG\n"); |
| return -1; |
| } |
| #ifndef NO_PRINT |
| 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<NN-KK+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 <= NN-KK) { /* 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] != A0)) { |
| discr_r ^= Alpha_to[modnn(Index_of[lambda[i]] + s[r - i])]; |
| } |
| } |
| discr_r = Index_of[discr_r]; /* Index form */ |
| if (discr_r == A0) { |
| /* 2 lines below: B(x) <-- x*B(x) */ |
| COPYDOWN(&b[1],b,NN-KK); |
| b[0] = A0; |
| } else { |
| /* 7 lines below: T(x) <-- lambda(x) - discr_r*x*b(x) */ |
| t[0] = lambda[0]; |
| for (i = 0 ; i < NN-KK; 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 <= NN-KK; i++) |
| b[i] = (lambda[i] == 0) ? A0 : modnn(Index_of[lambda[i]] - discr_r + NN); |
| } else { |
| /* 2 lines below: B(x) <-- x*B(x) */ |
| COPYDOWN(&b[1],b,NN-KK); |
| b[0] = A0; |
| } |
| COPY(lambda,t,NN-KK+1); |
| } |
| } |
| |
| /* Convert lambda to index form and compute deg(lambda(x)) */ |
| deg_lambda = 0; |
| for(i=0; i<NN-KK+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 |
| */ |
| COPY(®[1],&lambda[1],NN-KK); |
| count = 0; /* Number of roots of lambda(x) */ |
| for (i = 1; i <= NN; i++) { |
| q = 1; |
| for (j = deg_lambda; j > 0; j--) |
| if (reg[j] != A0) { |
| reg[j] = modnn(reg[j] + j); |
| q ^= Alpha_to[reg[j]]; |
| } |
| if (!q) { |
| /* store root (index-form) and error location number */ |
| root[count] = i; |
| loc[count] = NN - i; |
| count++; |
| } |
| } |
| |
| #ifdef DEBUG |
| printf("\n Final error positions:\t"); |
| for (i = 0; i < count; i++) |
| printf("%d ", loc[i]); |
| printf("\n"); |
| #endif |
| if (deg_lambda != count) { |
| /* |
| * deg(lambda) unequal to number of roots => uncorrectable |
| * error detected |
| */ |
| return -1; |
| } |
| /* |
| * Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo |
| * x**(NN-KK)). in index form. Also find deg(omega). |
| */ |
| deg_omega = 0; |
| for (i = 0; i < NN-KK; i++) { |
| tmp = 0; |
| j = (deg_lambda < i) ? deg_lambda : i; |
| for(; j >= 0; j--) { |
| if ((s[i + 1 - j] != A0) && (lambda[j] != A0)) |
| tmp ^= Alpha_to[modnn(s[i + 1 - j] + lambda[j])]; |
| } |
| if(tmp != 0) |
| deg_omega = i; |
| omega[i] = Index_of[tmp]; |
| } |
| omega[NN-KK] = A0; |
| |
| /* |
| * Compute error values in poly-form. num1 = omega(inv(X(l))), num2 = |
| * inv(X(l))**(B0-1) 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] * (B0 - 1) + NN)]; |
| den = 0; |
| |
| /* lambda[i+1] for i even is the formal derivative lambda_pr of lambda[i] */ |
| for (i = min(deg_lambda,NN-KK-1) & ~1; i >= 0; i -=2) { |
| if(lambda[i+1] != A0) |
| den ^= Alpha_to[modnn(lambda[i+1] + i * root[j])]; |
| } |
| if (den == 0) { |
| #ifdef DEBUG |
| printf("\n ERROR: denominator = 0\n"); |
| #endif |
| return -1; |
| } |
| /* Apply error to data */ |
| if (num1 != 0) { |
| data[loc[j]] ^= Alpha_to[modnn(Index_of[num1] + Index_of[num2] + NN - Index_of[den])]; |
| } |
| } |
| return count; |
| } |
| |
| |
| #endif /* USE_JPWL */ |
