Insert sort of binary file

bin_insert.c

void bininsert (FILE* f)
{
    if (!f) return;
    fseek(f, 0, 2);
    fpos_t i, j, n = ftell(f);
    int tmp, sd;
    for ( i = sizeof(int); i < n; i += sizeof(int) )
    {
        j = i - sizeof(int);
        fsetpos(f, &i);
        fread(&tmp, sizeof(int), 1, f);
        for ( ; j >= 0 ; j -= sizeof(int))
        {
            fsetpos(f, &j);
            fseek(f,0,1);
            fread(&sd, sizeof(int), 1,f);
            if (sd <= tmp) break;
	    fseek(f,0,1);
            fwrite(&sd,sizeof(int), 1,f);
        }
        //if ( i == ftell(f)) continue;
	fseek(f,0,1);
        if ( j < 0 ) rewind(f);
        fwrite (&tmp, sizeof(int), 1, f);
    }
}