text: /*
   * qrencode - QR Code encoder
   *
   * Reed solomon encoder. This code is taken from Phil Karn's libfec then
   * editted and packed into a pair of .c and .h files.
   *
   * Copyright (C) 2002, 2003, 2004, 2006 Phil Karn, KA9Q
   * (libfec is released under the GNU Lesser General Public License.)
   *
   * Copyright (C) 2006-2011 Kentaro Fukuchi <kentaro@fukuchi.org>
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
   */
  
  #if HAVE_CONFIG_H
  # include "config.h"
  #endif
  #include <stdlib.h>
  #include <string.h>
  #ifdef HAVE_LIBPTHREAD
  #  include <pthread.h>
  #endif
  
  #include "rscode.h"
  
  /* Stuff specific to the 8-bit symbol version of the general purpose RS codecs
   *
   */
  typedef unsigned char data_t;
  
  
  /**
   * Reed-Solomon codec control block
   */
  struct _RS {
  	int mm;              /* Bits per symbol */
  	int nn;              /* Symbols per block (= (1<<mm)-1) */
  	data_t *alpha_to;     /* log lookup table */
  	data_t *index_of;     /* Antilog lookup table */
  	data_t *genpoly;      /* Generator polynomial */
  	int nroots;     /* Number of generator roots = number of parity symbols */
  	int fcr;        /* First consecutive root, index form */
  	int prim;       /* Primitive element, index form */
  	int iprim;      /* prim-th root of 1, index form */
  	int pad;        /* Padding bytes in shortened block */
  	int gfpoly;
  	struct _RS *next;
  };
  
  static RS *rslist = NULL;
  #ifdef HAVE_LIBPTHREAD
  static pthread_mutex_t rslist_mutex = PTHREAD_MUTEX_INITIALIZER;
  #endif
  
  static int modnn(RS *rs, int x){
  	while (x >= rs->nn) {
  		x -= rs->nn;
  		x = (x >> rs->mm) + (x & rs->nn);
  	}
  	return x;
  }
  
  
  #define MODNN(x) modnn(rs,x)
  
  #define MM (rs->mm)
  #define NN (rs->nn)
  #define ALPHA_TO (rs->alpha_to) 
  #define INDEX_OF (rs->index_of)
  #define GENPOLY (rs->genpoly)
  #define NROOTS (rs->nroots)
  #define FCR (rs->fcr)
  #define PRIM (rs->prim)
  #define IPRIM (rs->iprim)
  #define PAD (rs->pad)
  #define A0 (NN)
  
  
  /* Initialize a Reed-Solomon codec
   * symsize = symbol size, bits
   * gfpoly = Field generator polynomial coefficients
   * fcr = first root of RS code generator polynomial, index form
   * prim = primitive element to generate polynomial roots
   * nroots = RS code generator polynomial degree (number of roots)
   * pad = padding bytes at front of shortened block
   */
  static RS *init_rs_char(int symsize, int gfpoly, int fcr, int prim, int nroots, int pad)
  {
    RS *rs;
  
  
  /* 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 > (int)(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 = (RS *)calloc(1,sizeof(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;
    rs->gfpoly = gfpoly;
  
    /* 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:;
  
    return rs;
  }
  
  RS *init_rs(int symsize, int gfpoly, int fcr, int prim, int nroots, int pad)
  {
  	RS *rs;
  
  #ifdef HAVE_LIBPTHREAD
  	pthread_mutex_lock(&rslist_mutex);
  #endif
  	for(rs = rslist; rs != NULL; rs = rs->next) {
  		if(rs->pad != pad) continue;
  		if(rs->nroots != nroots) continue;
  		if(rs->mm != symsize) continue;
  		if(rs->gfpoly != gfpoly) continue;
  		if(rs->fcr != fcr) continue;
  		if(rs->prim != prim) continue;
  
  		goto DONE;
  	}
  
  	rs = init_rs_char(symsize, gfpoly, fcr, prim, nroots, pad);
  	if(rs == NULL) goto DONE;
  	rs->next = rslist;
  	rslist = rs;
  
  DONE:
  #ifdef HAVE_LIBPTHREAD
  	pthread_mutex_unlock(&rslist_mutex);
  #endif
  	return rs;
  }
  
  
  void free_rs_char(RS *rs)
  {
  	free(rs->alpha_to);
  	free(rs->index_of);
  	free(rs->genpoly);
  	free(rs);
  }
  
  void free_rs_cache(void)
  {
  	RS *rs, *next;
  
  #ifdef HAVE_LIBPTHREAD
  	pthread_mutex_lock(&rslist_mutex);
  #endif
  	rs = rslist;
  	while(rs != NULL) {
  		next = rs->next;
  		free_rs_char(rs);
  		rs = next;
  	}
  	rslist = NULL;
  #ifdef HAVE_LIBPTHREAD
  	pthread_mutex_unlock(&rslist_mutex);
  #endif
  }
  
  /* The guts of the Reed-Solomon encoder, 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-NROOTS-PAD and type data_t to be encoded
   * data_t parity[] - an array of NROOTS and type data_t to be written with parity symbols
   * 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.
   * GENPOLY - an array of NROOTS+1 elements containing the generator polynomial in index form
  
   * The memset() and memmove() functions are used. The appropriate header
   * file declaring these functions (usually <string.h>) must be included by the calling
   * program.
  
   * Copyright 2004, Phil Karn, KA9Q
   * May be used under the terms of the GNU Lesser General Public License (LGPL)
   */
  
  #undef A0
  #define A0 (NN) /* Special reserved value encoding zero in index form */
  
  void encode_rs_char(RS *rs, const data_t *data, data_t *parity)
  {
    int i, j;
    data_t feedback;
  
    memset(parity,0,NROOTS*sizeof(data_t));
  
    for(i=0;i<NN-NROOTS-PAD;i++){
      feedback = INDEX_OF[data[i] ^ parity[0]];
      if(feedback != A0){      /* feedback term is non-zero */
  #ifdef UNNORMALIZED
        /* This line is unnecessary when GENPOLY[NROOTS] is unity, as it must
         * always be for the polynomials constructed by init_rs()
         */
        feedback = MODNN(NN - GENPOLY[NROOTS] + feedback);
  #endif
        for(j=1;j<NROOTS;j++)
  	parity[j] ^= ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS-j])];
      }
      /* Shift */
      memmove(&parity[0],&parity[1],sizeof(data_t)*(NROOTS-1));
      if(feedback != A0)
        parity[NROOTS-1] = ALPHA_TO[MODNN(feedback + GENPOLY[0])];
      else
        parity[NROOTS-1] = 0;
    }
  }
  