RS码FEC机制的实现方法（基于Luigi Rizzo的代码）
Luigi Rizzo大神在1997年写了一个基于范德蒙矩阵的FEC的纠错代码，这套代码本身开源并且在多个知名项目被使用。我基于这套fec代码，也做了一份RS纠错的例子。
Rizzo, L., "Effective Erasure Codes for Reliable Computer Communication Protocols",
ACM SIGCOMM Computer Communication Review, Vol.27, No.2, pp.24-36,April 1997.
Rizzo, L., "Reed-Solomon FEC codec (C language)",original codec: http://info.iet.unipi.it/~luigi/vdm98/vdm980702.tgz,
improved codec: http://openfec.org/,July 1998.Luigi Rizzo的代码仅包含fec.h和fec.c两个文件。
写一个包装方法rs.c和rs.h，代码如下：
rs.h的代码：
#ifndef LIB_RS_H_
#define LIB_RS_H_
#include "fec.h"
// input:
// code, generated by fec_new() function from fec.h
// data[0....k-1 ], points to original data
// size, data length
//
// output:
// data[k....n-1], points to generated redundant data
//
// info:
// the function will always succeed,except malloc fail.if malloc fail,it will call exit()
void rs_encode(void *code,char *data[],int size);
// input:
// data[0.....n-1] points to original data and redundate data,in right order
// if data[i] is missing ,set poniter data[i] to 0 (point it to null)
//
// outout:
// data[0.....k-1] will point to the recovered original data.
//
// info:
// return zero on success
// if the number of no-zero pointers is less than k,the function will fail and return non-zero
//
// advanced info:
// 1. rs_decode wont malloc memory for those zero pointers in data[0.....k-1]. instead it will re-use the memory of other non-zero pointers (and let data[0.....k-1] point to those memory).
// 2. if the input data[0.....n-1] contains x non-zero pointers,after called rs_decode,there will still be exactly x non-zero poninters in data[0.....n-1],just the order may change.
int rs_decode(void *code,char *data[],int size);
void rs_encode2(int k,int n,char *data[],int size);
int rs_decode2(int k,int n,char *data[],int size);
#endif /* LIB_RS_H_ */rs.c的代码：
#include "rs.h"
#include "stdlib.h"
#include "string.h"
#include "stdio.h"
void rs_encode(void *code,char *data[],int size)
{
int k=get_k(code);
int n=get_n(code);
printf("encode k:%d n:%d\n",k,n );
for(int i=k;imain函数的例子代码：
#include
#include "rs.h"
int main(int argc, char *argv[])
{
int i,j,k;
char arr[6][100]=
{
"aaa","bbb","ccc"
,"ddd","eee","fff"
};
char *data[6];
for(i=0;i<6;i++)
{
data[i]=arr[i];
}
for(i=0;i<6;i++)
{
printf("before rs encode: <%s>\n",data[i]);
}
//6 strings protect 5 strings.
rs_encode2(5,6,data,3);
for(i=0;i<6;i++)
{
printf("after rs encode: <%s>\n",data[i]);
}
//simulate lost data.
data[0]=0; // 0 is NULL.
//data[1]=0;
//data[2]=0;
int ret=rs_decode2(5,6,data,3);
for(i=0;i<6;i++)
{
printf("after rs decode: <%s>\n",data[i]);
}
return 0;
} 在main函数生成了6个字符串，通过rs_encode2将前5个字符串保护起来，第6个字符串用来存冗余数据。
data[0]=0模拟了丢失数据，然后通过rs_decode2来恢复数据。
输出如下：
before rs encode:
before rs encode:
before rs encode:
before rs encode:
before rs encode:
before rs encode:
encode k:5 n:6
after rs encode:
after rs encode:
after rs encode:
after rs encode:
after rs encode:
after rs encode: <���>
decode k:5 n:6
after rs decode:
after rs decode:
after rs decode:
after rs decode:
after rs decode:
after rs decode: <(null)>
可见aaa,bbb,ccc,ddd,eee得到了恢复，在《我的下载资源》中有完整代码