Good optimisation. In C you can of course avoid the copy and move overhead of the substr buffer you use and just flip pointers between a pair of buffers to get the sliding window.
Runtime on a 1GHz laptop was 10 minutes on a 3GB test file. So the benefits of doing it in C are real but perhaps hardly worth the effort unless saving 20 minutes runtime for adding X minutes coding time makes sense.
$ cat file.c
#include <stdio.h>
#define FILENAME "c:\\test.txt"
#define CHUNK 500
int main()
{
FILE *f;
char buf1[CHUNK],buf2[CHUNK],pair[3],*fbuf,*bbuf,*swap;
int r, i;
f=fopen(FILENAME,"r");
if (!f)
return 1;
fbuf=buf1;
bbuf=buf2;
r=(int)fread( fbuf, sizeof(char), CHUNK, f );
if ( !r || r<CHUNK )
return 1;
pair[2]=0;
while ( (r=(int)fread( bbuf, sizeof(char), CHUNK, f )) ) {
for( i=0;i<r;i++ ) {
pair[0]=fbuf[i];
pair[1]=bbuf[i];
/* printf("%s\n",pair);*/
}
/* Move old back buffer pointer to front buffer ptr
* And vice versa. Net effect is to slide buffer->R
* As we will refil the back buffer with fresh data.
* Thus we simply pour data from disk to memory with
* no wasted copying effort.
*/
swap=fbuf;
fbuf=bbuf;
bbuf=swap;
}
fclose(f);
return 0;
}
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