rem: memset(sum,0,csum_length);
add: memset(sum,0,MD4_SUM_LENGTH);
context: void file_checksum(char *fname,char *sum,OFF_T size){	OFF_T i;	struct map_struct *buf;	int fd;	OFF_T len = size;	char tmpchunk[CSUM_CHUNK];	struct mdfour m;		memset(sum,0,csum_length);		fd = open(fname,O_RDONLY);	if (fd == -1) return;		buf = map_file(fd,size);		mdfour_begin(&m);	for(i = 0; i + CSUM_CHUNK <= len; i += CSUM_CHUNK) {		memcpy(tmpchunk, map_ptr(buf,i,CSUM_CHUNK), CSUM_CHUNK);		mdfour_update(&m, (uchar *)tmpchunk, CSUM_CHUNK);	}	if (len - i > 0) {		memcpy(tmpchunk, map_ptr(buf,i,len-i), len-i);		mdfour_update(&m, (uchar *)tmpchunk, (len-i));	}	mdfour_result(&m, (uchar *)sum);	close(fd);	unmap_file(buf);}