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58 lines
2.3 KiB
58 lines
2.3 KiB
/* The guts of the Reed-Solomon encoder, meant to be #included |
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* into a function body with the following typedefs, macros and variables supplied |
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* according to the code parameters: |
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* data_t - a typedef for the data symbol |
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* data_t data[] - array of NN-NROOTS-PAD and type data_t to be encoded |
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* data_t parity[] - an array of NROOTS and type data_t to be written with parity symbols |
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* NROOTS - the number of roots in the RS code generator polynomial, |
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* which is the same as the number of parity symbols in a block. |
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Integer variable or literal. |
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* |
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* NN - the total number of symbols in a RS block. Integer variable or literal. |
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* PAD - the number of pad symbols in a block. Integer variable or literal. |
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* ALPHA_TO - The address of an array of NN elements to convert Galois field |
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* elements in index (log) form to polynomial form. Read only. |
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* INDEX_OF - The address of an array of NN elements to convert Galois field |
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* elements in polynomial form to index (log) form. Read only. |
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* MODNN - a function to reduce its argument modulo NN. May be inline or a macro. |
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* GENPOLY - an array of NROOTS+1 elements containing the generator polynomial in index form |
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* The memset() and memmove() functions are used. The appropriate header |
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* file declaring these functions (usually <string.h>) must be included by the calling |
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* program. |
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* Copyright 2004, Phil Karn, KA9Q |
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* May be used under the terms of the GNU Lesser General Public License (LGPL) |
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*/ |
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#undef A0 |
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#define A0 (NN) /* Special reserved value encoding zero in index form */ |
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{ |
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int i, j; |
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data_t feedback; |
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memset(parity,0,NROOTS*sizeof(data_t)); |
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for(i=0;i<NN-NROOTS-PAD;i++){ |
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feedback = INDEX_OF[data[i] ^ parity[0]]; |
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if(feedback != A0){ /* feedback term is non-zero */ |
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#ifdef UNNORMALIZED |
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/* This line is unnecessary when GENPOLY[NROOTS] is unity, as it must |
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* always be for the polynomials constructed by init_rs() |
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*/ |
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feedback = MODNN(NN - GENPOLY[NROOTS] + feedback); |
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#endif |
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for(j=1;j<NROOTS;j++) |
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parity[j] ^= ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS-j])]; |
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} |
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/* Shift */ |
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memmove(&parity[0],&parity[1],sizeof(data_t)*(NROOTS-1)); |
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if(feedback != A0) |
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parity[NROOTS-1] = ALPHA_TO[MODNN(feedback + GENPOLY[0])]; |
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else |
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parity[NROOTS-1] = 0; |
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} |
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}
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