X-Git-Url: https://git.gag.com/?a=blobdiff_plain;f=gnuradio-core%2Fsrc%2Flib%2Freed-solomon%2Frs.3;fp=gnuradio-core%2Fsrc%2Flib%2Freed-solomon%2Frs.3;h=c3953ce57a108b3ce53ef2957b36e3d892cb18a1;hb=8a9ddbb0675f9bfcc6e03b457fba6c79474a3693;hp=0000000000000000000000000000000000000000;hpb=82d471b9b4a8b389b5da44b19c69c36420828382;p=debian%2Fgnuradio diff --git a/gnuradio-core/src/lib/reed-solomon/rs.3 b/gnuradio-core/src/lib/reed-solomon/rs.3 new file mode 100644 index 00000000..c3953ce5 --- /dev/null +++ b/gnuradio-core/src/lib/reed-solomon/rs.3 @@ -0,0 +1,170 @@ +.TH REED-SOLOMON 3 +.SH NAME +init_rs_int, encode_rs_int, decode_rs_int, free_rs_int, +init_rs_char, encode_rs_char, decode_rs_char, free_rs_char, +encode_rs_8, decode_rs_8, encode_rs_ccsds, decode_rs_ccsds +.SH SYNOPSIS +.nf +.ft B +#include "rs.h" + +void *init_rs_int(unsigned int symsize,unsigned int gfpoly,unsigned fcr, +unsigned prim,unsigned int nroots); +void encode_rs_int(void *rs,int *data,int *parity); +int decode_rs_int(void *rs,int *data,int *eras_pos,int no_eras); +void free_rs_int(void *rs); + +void *init_rs_char(unsigned int symsize,unsigned int gfpoly,unsigned fcr, +unsigned prim,unsigned int nroots); +void encode_rs_char(void *rs,unsigned char *data,unsigned char *parity); +int decode_rs_char(void *rs,unsigned char *data,int *eras_pos,int no_eras); +void free_rs_char(void *rs); + +void encode_rs_8(unsigned char *data,unsigned char *parity); +int decode_rs_8(unsigned char *data,int *eras_pos,int no_eras); + +void encode_rs_ccsds(unsigned char *data,unsigned char *parity); +int decode_rs_ccsds(unsigned char *data,int *eras_pos,int no_eras); + +unsigned char Taltab[256]; +unsigned char Tal1tab[256]; + +.fi + +.SH DESCRIPTION +These functions implement Reed-Solomon error control encoding and +decoding. For optimal performance in a variety of applications, three +sets of functions are supplied. To access these functions, add "-lrs" +to your linker command line. + +The functions with names ending in "_int" handle data in integer arrays, +permitting arbitrarily large codewords limited only by machine +resources. + +The functions with names ending in "_char" take unsigned char arrays and can +handle codes with symbols of 8 bits or less (i.e., with codewords of +255 symbols or less). + +\fBencode_rs_8\fR and \fBdecode_rs_8\fR implement a specific +(255,223) code with 8-bit symbols specified by the CCSDS: +a field generator of 1 + X + X^2 + X^7 + X^8 and a code +generator with first consecutive root = 112 and a primitive element of +11. These functions use the conventional +polynomial form, \fBnot\fR the dual-basis specified in +the CCSDS standard, to represent symbols. + +For full CCSDS compatibility, \fBencode_rs_ccsds\fR and +\fBdecode_rs_ccsds\fR are provided. These functions use two lookup +tables, \fBTaltab\fR to convert from conventional to dual-basis, and +\fBTal1tab\fR to perform the inverse mapping from dual-basis to +conventional form, before and after calls to \fBencode_rs_8\fR +and \fBdecode_rs_8\fR. + +The _8 and _ccsds functions do not require initialization. +To use the general purpose RS encoder or decoder (i.e., +the _char or _int versions), the user must first +call \fBinit_rs_int\fR or \fBinit_rs_char\fR as appropriate. The +arguments are as follows: + +\fBsymsize\fR gives the symbol size in bits, up to 8 for \fBinit_rs_char\fR +or 32 for \fBinit_rs_int\fR on a machine with 32-bit ints (though such a +huge code would exhaust memory limits on a 32-bit machine). The resulting +Reed-Solomon code word will have 2^\fBsymsize\fR - 1 symbols, +each containing \fBsymsize\fR bits. + +\fBgfpoly\fR gives the extended Galois field generator polynomial coefficients, +with the 0th coefficient in the low order bit. The polynomial +\fImust\fR be primitive; if not, the call will fail and NULL will be +returned. + +\fBfcr\fR gives, in index form, the first consecutive root of the +Reed Solomon code generator polynomial. + +\fBprim\fR gives, in index form, the primitive element in the Galois field +used to generate the Reed Solomon code generator polynomial. + +\fBnroots\fR gives the number of roots in the Reed Solomon code +generator polynomial. This equals the number of parity symbols +per code block. + +The resulting Reed-Solomon code has parameters (N,K), where +N = 2^\fBsymsize\fR-1 and K = N-\fBnroots\fR. + +The \fBencode_rs_char\fR and \fBencode_rs_int\fR functions accept +the pointer returned by \fBinit_rs_char\fR or +\fBinit_rs_int\fR, respectively, to +encode a block of data using the specified code. +The input data array is expected to +contain K symbols (of \fBsymsize\fR bits each, right justified +in each char or int) and \fBnroots\fR parity symbols will be placed +into the \fBparity\fR array, right justified. + +The \fBdecode_rs_char\fR and \fBdecode_rs_int\fR functions correct +the errors in a Reed-Solomon codeword up to the capability of the code. +An optional list of "erased" symbol indices may be given in the \fBeras_pos\fR +array to assist the decoder; this parameter may be NULL if no erasures +are given. The number of erased symbols must be given in the \fBno_eras\fR +parameter. + +To maximize performance, the encode and decode functions perform no +"sanity checking" of their inputs. Decoder failure may result if +\fBeras_pos\fR contains duplicate entries, and both encoder and +decoder will fail if an input symbol exceeds its allowable range. +(Symbol range overflow cannot occur with the _8 or _ccsds functions, +or with the _char functions when 8-bit symbols are specified.) + +The decoder corrects the symbols "in place", returning the number +of symbols in error. If the codeword is uncorrectable, -1 is returned +and the data block is unchanged. If \fBeras_pos\fR is non-null, it is +used to return a list of corrected symbol positions, in no particular +order. This means that the +array passed through this parameter \fImust\fR have at least \fBnroots\fR +elements to prevent a possible buffer overflow. + +The \fBfree_rs_int\fR and \fBfree_rs_char\fR functions free the internal +space allocated by the \fBinit_rs_int\fR and \fBinit_rs_char\fR functions, +respecitively. + +The functions \fBencode_rs_8\fR and \fBdecode_rs_8\fR do not have +corresponding \fBinit\fR and \fBfree\fR, nor do they take the +\fBrs\fR argument accepted by the other functions as their parameters +are statically compiled. These functions implement a code +equivalent to calling + +\fBinit_rs_char\fR(8,0x187,112,11,32); + +and using the resulting pointer with \fBencode_rs_char\fR and +\fBdecode_rs_char\fR. + +.SH RETURN VALUES +\fBinit_rs_int\fR and \fBinit_rs_char\fR return a pointer to an internal +control structure that must be passed to the corresponding encode, decode +and free functions. These functions return NULL on error. + +The decode functions return a count of corrected +symbols, or -1 if the block was uncorrectible. + +.SH AUTHOR +Phil Karn, KA9Q (karn@ka9q.net), based heavily on earlier work by Robert +Morelos-Zaragoza (rober@spectra.eng.hawaii.edu) and Hari Thirumoorthy +(harit@spectra.eng.hawaii.edu). + +.SH COPYRIGHT +Copyright 2002, Phil Karn, KA9Q. May be used under the terms of the +GNU General Public License (GPL). + +.SH SEE ALSO +CCSDS 101.0-B-5: Telemetry Channel Coding. +http://www.ccsds.org/documents/pdf/CCSDS-101.0-B-5.pdf + +.SH NOTE +CCSDS chose the "dual basis" symbol representation because it +simplified the implementation of a Reed-Solomon encoder in dedicated +hardware. However, this approach holds no advantages for a software +implementation on a general purpose computer, so use of the dual basis +is recommended only if compatibility with the CCSDS standard is needed, +e.g., to decode data from an existing spacecraft using the CCSDS +standard. If you just want a fast (255,223) RS codec without needing +to interoperate with a CCSDS standard code, use \fBencode_rs_8\fR +and \fBdecode_rs_8\fR. +