X-Git-Url: https://git.sur5r.net/?p=iec16022;a=blobdiff_plain;f=reedsol.c;h=a828783dd63afb2e623ed5a594fab1c2b4ecd1dd;hp=13f71bba9cb4c158d245a7fb92c9b391a6abf66c;hb=HEAD;hpb=81dd1b1b5dfd4246f61ec1ccda6a297bc398673c diff --git a/reedsol.c b/reedsol.c index 13f71bb..a828783 100644 --- a/reedsol.c +++ b/reedsol.c @@ -1,4 +1,4 @@ -/** +/** * * This is a simple Reed-Solomon encoder * (C) Cliff Hones 2004 @@ -17,8 +17,7 @@ * along with this program; if not, write to the Free Software * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA * - */ - + */ // It is not written with high efficiency in mind, so is probably // not suitable for real-time encoding. The aim was to keep it @@ -39,17 +38,15 @@ // malloc/free can be avoided by using static arrays of a suitable // size. -#include // only needed for debug (main) -#include // only needed for malloc/free +#include // only needed for debug (main) +#include // only needed for malloc/free static int gfpoly; -static int symsize; // in bits -static int logmod; // 2**symsize - 1 +static int symsize; // in bits +static int logmod; // 2**symsize - 1 static int rlen; -static int *log = NULL, - *alog = NULL, - *rspoly = NULL; +static int *log = NULL, *alog = NULL, *rspoly = NULL; // rs_init_gf(poly) initialises the parameters for the Galois Field. // The symbol size is determined from the highest bit set in poly @@ -61,42 +58,37 @@ static int *log = NULL, // polynomial. e.g. for ECC200 (8-bit symbols) the polynomial is // a**8 + a**5 + a**3 + a**2 + 1, which translates to 0x12d. -void rs_init_gf (int poly) +void rs_init_gf(int poly) { - int m, - b, - p, - v; - - // Return storage from previous setup - if (log) - { - free (log); - free (alog); - free (rspoly); - rspoly = NULL; - } - // Find the top bit, and hence the symbol size - for (b = 1, m = 0; b <= poly; b <<= 1) - m++; - b >>= 1; - m--; - gfpoly = poly; - symsize = m; - - // Calculate the log/alog tables - logmod = (1 << m) - 1; - log = (int *) malloc (sizeof (int) * (logmod + 1)); - alog = (int *) malloc (sizeof (int) * logmod); - - for (p = 1, v = 0; v < logmod; v++) - { - alog[v] = p; - log[p] = v; - p <<= 1; - if (p & b) - p ^= poly; - } + int m, b, p, v; + + // Return storage from previous setup + if (log) { + free(log); + free(alog); + free(rspoly); + rspoly = NULL; + } + // Find the top bit, and hence the symbol size + for (b = 1, m = 0; b <= poly; b <<= 1) + m++; + b >>= 1; + m--; + gfpoly = poly; + symsize = m; + + // Calculate the log/alog tables + logmod = (1 << m) - 1; + log = (int *)malloc(sizeof(int) * (logmod + 1)); + alog = (int *)malloc(sizeof(int) * logmod); + + for (p = 1, v = 0; v < logmod; v++) { + alog[v] = p; + log[p] = v; + p <<= 1; + if (p & b) + p ^= poly; + } } // rs_init_code(nsym, index) initialises the Reed-Solomon encoder @@ -106,78 +98,75 @@ void rs_init_gf (int poly) // (x + 2**i)*(x + 2**(i+1))*... [nsym terms] // For ECC200, index is 1. -void rs_init_code (int nsym, int index) +void rs_init_code(int nsym, int index) { - int i, - k; - - if (rspoly) - free (rspoly); - rspoly = (int *) malloc (sizeof (int) * (nsym + 1)); - - rlen = nsym; - - rspoly[0] = 1; - for (i = 1; i <= nsym; i++) - { - rspoly[i] = 1; - for (k = i - 1; k > 0; k--) - { - if (rspoly[k]) - rspoly[k] = alog[(log[rspoly[k]] + index) % logmod]; - rspoly[k] ^= rspoly[k - 1]; - } - rspoly[0] = alog[(log[rspoly[0]] + index) % logmod]; - index++; - } + int i, k; + + if (rspoly) + free(rspoly); + rspoly = (int *)malloc(sizeof(int) * (nsym + 1)); + + rlen = nsym; + + rspoly[0] = 1; + for (i = 1; i <= nsym; i++) { + rspoly[i] = 1; + for (k = i - 1; k > 0; k--) { + if (rspoly[k]) + rspoly[k] = + alog[(log[rspoly[k]] + index) % logmod]; + rspoly[k] ^= rspoly[k - 1]; + } + rspoly[0] = alog[(log[rspoly[0]] + index) % logmod]; + index++; + } } // Note that the following uses byte arrays, so is only suitable for // symbol sizes up to 8 bits. Just change the data type of data and res // to unsigned int * for larger symbols. -void rs_encode (int len, unsigned char *data, unsigned char *res) +void rs_encode(int len, unsigned char *data, unsigned char *res) { - int i, - k, - m; - for (i = 0; i < rlen; i++) - res[i] = 0; - for (i = 0; i < len; i++) - { - m = res[rlen - 1] ^ data[i]; - for (k = rlen - 1; k > 0; k--) - { - if (m && rspoly[k]) - res[k] = res[k - 1] ^ alog[(log[m] + log[rspoly[k]]) % logmod]; - else - res[k] = res[k - 1]; - } - if (m && rspoly[0]) - res[0] = alog[(log[m] + log[rspoly[0]]) % logmod]; - else - res[0] = 0; - } + int i, k, m; + for (i = 0; i < rlen; i++) + res[i] = 0; + for (i = 0; i < len; i++) { + m = res[rlen - 1] ^ data[i]; + for (k = rlen - 1; k > 0; k--) { + if (m && rspoly[k]) + res[k] = + res[k - + 1] ^ alog[(log[m] + + log[rspoly[k]]) % logmod]; + else + res[k] = res[k - 1]; + } + if (m && rspoly[0]) + res[0] = alog[(log[m] + log[rspoly[0]]) % logmod]; + else + res[0] = 0; + } } #ifndef LIB // The following tests the routines with the ISO/IEC 16022 Annexe R data -int main (void) +int reedsol_main(void) { - register int i; + register int i; - unsigned char data[9] = { 142, 164, 186 }; - unsigned char out[5]; + unsigned char data[9] = { 142, 164, 186 }; + unsigned char out[5]; - rs_init_gf (0x12d); - rs_init_code (5, 1); + rs_init_gf(0x12d); + rs_init_code(5, 1); - rs_encode (3, data, out); + rs_encode(3, data, out); - printf ("Result of Annexe R encoding:\n"); - for (i = 4; i >= 0; i--) - printf (" %d\n", out[i]); + printf("Result of Annexe R encoding:\n"); + for (i = 4; i >= 0; i--) + printf(" %d\n", out[i]); - return 0; + return 0; } #endif