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sum1.c revision 1.1 
      1 /*-
      2  * Copyright (c) 1991 The Regents of the University of California.
      3  * All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  * 1. Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  * 2. Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in the
     12  *    documentation and/or other materials provided with the distribution.
     13  * 3. All advertising materials mentioning features or use of this software
     14  *    must display the following acknowledgement:
     15  *	This product includes software developed by the University of
     16  *	California, Berkeley and its contributors.
     17  * 4. Neither the name of the University nor the names of its contributors
     18  *    may be used to endorse or promote products derived from this software
     19  *    without specific prior written permission.
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     31  * SUCH DAMAGE.
     32  */
     33 
     34 #ifndef lint
     35 static char sccsid[] = "@(#)sum1.c	5.1 (Berkeley) 4/4/91";
     36 #endif /* not lint */
     37 
     38 #include <sys/types.h>
     39 #include <unistd.h>
     40 
     41 csum1(fd, cval, clen)
     42 	register int fd;
     43 	u_long *cval, *clen;
     44 {
     45 	register u_long total;
     46 	register int nr;
     47 	register u_int crc;
     48 	register u_char *p;
     49 	u_char buf[8192];
     50 
     51 	/*
     52 	 * 16-bit checksum, rotating right before each addition;
     53 	 * overflow is discarded.
     54 	 */
     55 	crc = total = 0;
     56 	while ((nr = read(fd, buf, sizeof(buf))) > 0)
     57 		for (total += nr, p = buf; nr--; ++p) {
     58 			if (crc & 1)
     59 				crc |= 0x10000;
     60 			crc = ((crc >> 1) + *p) & 0xffff;
     61 		}
     62 	if (nr < 0)
     63 		return(1);
     64 
     65 	*cval = crc;
     66 	*clen = total;
     67 	return(0);
     68 }
     69