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akimasa/tshead.c

Last active January 26, 2016 13:55
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http://technica-blog.jp/1159 の下にあるコードをC言語で高速に？ 読み込んだファイルは頭出し後、STDOUTに出力
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tshead.c
#define _LARGEFILE_SOURCE
#define _FILE_OFFSET_BITS 64
#include <stdio.h>
#include <stdlib.h>
#ifdef _WIN32
#include <io.h>
#include <fcntl.h>
#endif
int main(int argc, char *argv[0]){
#ifdef _WIN32
setmode(fileno(stdout),O_BINARY);
setmode(fileno(stdin),O_BINARY);
#endif
FILE *fp;
unsigned char buf[188];
int pid,pmt,fore_pid;
pmt = -1;
fore_pid = 0;
if((fp = fopen(argv[1], "rb")) == NULL) {
fprintf(stderr,"file open error");
exit(EXIT_FAILURE);
}
//printf("%d,%d\n",(int)sizeof(buf[0]),(int)(sizeof(buf)/sizeof(buf[0])));
while(fread(buf, sizeof(buf[0]),sizeof(buf)/sizeof(buf[0]),fp)){
if(buf[0] != 0x47){
fprintf(stderr,"not sync\n");
fclose(fp);
exit(EXIT_FAILURE);
}
pid = (((buf[1] & 0x1f) << 8) | buf[2]);
if(pid == 0x00 && pmt == -1){
pmt = (((buf[19] & 0x1f) << 8) | buf[20]);
}
if(pmt != 0 && pid == pmt && ((buf[1]&0x40) == 0x40)){
int plen = ((buf[15]&0xf) * 16 * 16) + buf[16];
int index = 17 + plen;
int currentpid;
if(index+19 > 188){
fprintf(stderr,"index err\n");
fclose(fp);
exit(EXIT_FAILURE);
}
if(buf[index] == 0x02){
currentpid = (buf[index+1]<<8) | buf[index+2];
}
if(fore_pid != 0 && fore_pid != currentpid){
fprintf(stderr,"pid changed%d,%d\n",fore_pid,currentpid);
size_t rcount;
//unsigned char largebuf[1024*1024*1];
int largebufsize = 1024*1024*1;
unsigned char *largebuf = (unsigned char *)malloc(largebufsize);
while((rcount = fread(largebuf, 1,largebufsize,fp))){
fwrite(largebuf, 1, rcount,stdout);
}
fclose(fp);
exit(EXIT_SUCCESS);
}
fore_pid = currentpid;
}
}
printf("hoge\n");
fclose(fp);
}
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