forked from rrcarlosr/Jetpack
290 lines
8.0 KiB
Cheetah
290 lines
8.0 KiB
Cheetah
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
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<book id="Reed-Solomon-Library-Guide">
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<bookinfo>
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<title>Reed-Solomon Library Programming Interface</title>
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<authorgroup>
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<author>
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<firstname>Thomas</firstname>
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<surname>Gleixner</surname>
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<affiliation>
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<address>
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<email>tglx@linutronix.de</email>
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</address>
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</affiliation>
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</author>
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</authorgroup>
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<copyright>
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<year>2004</year>
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<holder>Thomas Gleixner</holder>
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</copyright>
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<legalnotice>
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<para>
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This documentation is free software; you can redistribute
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it and/or modify it under the terms of the GNU General Public
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License version 2 as published by the Free Software Foundation.
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</para>
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<para>
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This program is distributed in the hope that it will be
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useful, but WITHOUT ANY WARRANTY; without even the implied
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warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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See the GNU General Public License for more details.
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</para>
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<para>
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You should have received a copy of the GNU General Public
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License along with this program; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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MA 02111-1307 USA
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</para>
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<para>
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For more details see the file COPYING in the source
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distribution of Linux.
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</para>
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</legalnotice>
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</bookinfo>
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<toc></toc>
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<chapter id="intro">
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<title>Introduction</title>
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<para>
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The generic Reed-Solomon Library provides encoding, decoding
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and error correction functions.
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</para>
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<para>
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Reed-Solomon codes are used in communication and storage
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applications to ensure data integrity.
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</para>
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<para>
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This documentation is provided for developers who want to utilize
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the functions provided by the library.
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</para>
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</chapter>
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<chapter id="bugs">
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<title>Known Bugs And Assumptions</title>
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<para>
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None.
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</para>
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</chapter>
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<chapter id="usage">
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<title>Usage</title>
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<para>
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This chapter provides examples of how to use the library.
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</para>
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<sect1>
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<title>Initializing</title>
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<para>
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The init function init_rs returns a pointer to an
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rs decoder structure, which holds the necessary
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information for encoding, decoding and error correction
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with the given polynomial. It either uses an existing
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matching decoder or creates a new one. On creation all
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the lookup tables for fast en/decoding are created.
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The function may take a while, so make sure not to
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call it in critical code paths.
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</para>
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<programlisting>
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/* the Reed Solomon control structure */
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static struct rs_control *rs_decoder;
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/* Symbolsize is 10 (bits)
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* Primitive polynomial is x^10+x^3+1
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* first consecutive root is 0
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* primitive element to generate roots = 1
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* generator polynomial degree (number of roots) = 6
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*/
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rs_decoder = init_rs (10, 0x409, 0, 1, 6);
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</programlisting>
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</sect1>
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<sect1>
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<title>Encoding</title>
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<para>
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The encoder calculates the Reed-Solomon code over
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the given data length and stores the result in
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the parity buffer. Note that the parity buffer must
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be initialized before calling the encoder.
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</para>
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<para>
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The expanded data can be inverted on the fly by
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providing a non-zero inversion mask. The expanded data is
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XOR'ed with the mask. This is used e.g. for FLASH
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ECC, where the all 0xFF is inverted to an all 0x00.
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The Reed-Solomon code for all 0x00 is all 0x00. The
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code is inverted before storing to FLASH so it is 0xFF
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too. This prevents that reading from an erased FLASH
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results in ECC errors.
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</para>
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<para>
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The databytes are expanded to the given symbol size
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on the fly. There is no support for encoding continuous
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bitstreams with a symbol size != 8 at the moment. If
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it is necessary it should be not a big deal to implement
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such functionality.
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</para>
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<programlisting>
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/* Parity buffer. Size = number of roots */
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uint16_t par[6];
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/* Initialize the parity buffer */
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memset(par, 0, sizeof(par));
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/* Encode 512 byte in data8. Store parity in buffer par */
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encode_rs8 (rs_decoder, data8, 512, par, 0);
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</programlisting>
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</sect1>
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<sect1>
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<title>Decoding</title>
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<para>
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The decoder calculates the syndrome over
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the given data length and the received parity symbols
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and corrects errors in the data.
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</para>
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<para>
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If a syndrome is available from a hardware decoder
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then the syndrome calculation is skipped.
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</para>
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<para>
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The correction of the data buffer can be suppressed
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by providing a correction pattern buffer and an error
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location buffer to the decoder. The decoder stores the
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calculated error location and the correction bitmask
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in the given buffers. This is useful for hardware
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decoders which use a weird bit ordering scheme.
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</para>
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<para>
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The databytes are expanded to the given symbol size
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on the fly. There is no support for decoding continuous
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bitstreams with a symbolsize != 8 at the moment. If
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it is necessary it should be not a big deal to implement
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such functionality.
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</para>
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<sect2>
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<title>
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Decoding with syndrome calculation, direct data correction
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</title>
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<programlisting>
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/* Parity buffer. Size = number of roots */
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uint16_t par[6];
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uint8_t data[512];
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int numerr;
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/* Receive data */
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.....
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/* Receive parity */
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.....
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/* Decode 512 byte in data8.*/
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numerr = decode_rs8 (rs_decoder, data8, par, 512, NULL, 0, NULL, 0, NULL);
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</programlisting>
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</sect2>
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<sect2>
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<title>
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Decoding with syndrome given by hardware decoder, direct data correction
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</title>
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<programlisting>
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/* Parity buffer. Size = number of roots */
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uint16_t par[6], syn[6];
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uint8_t data[512];
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int numerr;
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/* Receive data */
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.....
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/* Receive parity */
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.....
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/* Get syndrome from hardware decoder */
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.....
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/* Decode 512 byte in data8.*/
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numerr = decode_rs8 (rs_decoder, data8, par, 512, syn, 0, NULL, 0, NULL);
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</programlisting>
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</sect2>
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<sect2>
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<title>
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Decoding with syndrome given by hardware decoder, no direct data correction.
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</title>
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<para>
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Note: It's not necessary to give data and received parity to the decoder.
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</para>
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<programlisting>
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/* Parity buffer. Size = number of roots */
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uint16_t par[6], syn[6], corr[8];
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uint8_t data[512];
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int numerr, errpos[8];
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/* Receive data */
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.....
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/* Receive parity */
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.....
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/* Get syndrome from hardware decoder */
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.....
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/* Decode 512 byte in data8.*/
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numerr = decode_rs8 (rs_decoder, NULL, NULL, 512, syn, 0, errpos, 0, corr);
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for (i = 0; i < numerr; i++) {
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do_error_correction_in_your_buffer(errpos[i], corr[i]);
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}
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</programlisting>
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</sect2>
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</sect1>
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<sect1>
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<title>Cleanup</title>
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<para>
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The function free_rs frees the allocated resources,
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if the caller is the last user of the decoder.
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</para>
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<programlisting>
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/* Release resources */
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free_rs(rs_decoder);
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</programlisting>
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</sect1>
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</chapter>
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<chapter id="structs">
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<title>Structures</title>
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<para>
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This chapter contains the autogenerated documentation of the structures which are
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used in the Reed-Solomon Library and are relevant for a developer.
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</para>
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!Iinclude/linux/rslib.h
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</chapter>
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<chapter id="pubfunctions">
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<title>Public Functions Provided</title>
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<para>
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This chapter contains the autogenerated documentation of the Reed-Solomon functions
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which are exported.
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</para>
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!Elib/reed_solomon/reed_solomon.c
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</chapter>
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<chapter id="credits">
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<title>Credits</title>
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<para>
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The library code for encoding and decoding was written by Phil Karn.
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</para>
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<programlisting>
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Copyright 2002, Phil Karn, KA9Q
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May be used under the terms of the GNU General Public License (GPL)
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</programlisting>
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<para>
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The wrapper functions and interfaces are written by Thomas Gleixner.
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</para>
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<para>
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Many users have provided bugfixes, improvements and helping hands for testing.
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Thanks a lot.
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</para>
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<para>
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The following people have contributed to this document:
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</para>
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<para>
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Thomas Gleixner<email>tglx@linutronix.de</email>
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</para>
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</chapter>
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</book>
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