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Annotation of 43BSDTahoe/etc/timed/cksum.tahoe.c, revision 1.1.1.1

1.1       root        1: /*
                      2:  * Copyright (c) 1986 Regents of the University of California.
                      3:  * All rights reserved.
                      4:  *
                      5:  * Redistribution and use in source and binary forms are permitted
                      6:  * provided that the above copyright notice and this paragraph are
                      7:  * duplicated in all such forms and that any documentation,
                      8:  * advertising materials, and other materials related to such
                      9:  * distribution and use acknowledge that the software was developed
                     10:  * by the University of California, Berkeley.  The name of the
                     11:  * University may not be used to endorse or promote products derived
                     12:  * from this software without specific prior written permission.
                     13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
                     14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
                     15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
                     16:  */
                     17: 
                     18: #ifndef lint
                     19: static char sccsid[] = "@(#)cksum.tahoe.c      2.3 (Berkeley) 6/18/88";
                     20: #endif /* not lint */
                     21: 
                     22: #include <sys/types.h>
                     23: 
                     24: /*
                     25:  * Checksum routine for Internet Protocol family headers.
                     26:  *
                     27:  * This routine is very heavily used in the network
                     28:  * code and should be modified for each CPU to be as fast as possible.
                     29:  * 
                     30:  * This implementation is TAHOE version.
                     31:  */
                     32: 
                     33: #undef ADDCARRY
                     34: #define ADDCARRY(sum) { \
                     35:        if (sum & 0xffff0000) { \
                     36:                sum &= 0xffff; \
                     37:                sum++; \
                     38:        } \
                     39: }
                     40: 
                     41: in_cksum(addr, len)
                     42:        register u_short *addr;
                     43:        register int len;
                     44: {
                     45:        union word {
                     46:                char    c[2];
                     47:                u_short s;
                     48:        } u;
                     49:        register int sum = 0;
                     50: 
                     51:        while (len > 0) {
                     52:                /*
                     53:                 * add by words.
                     54:                 */
                     55:                while ((len -= 2) >= 0) {
                     56:                        if ((int)addr & 0x1) {
                     57:                                /* word is not aligned */
                     58:                                u.c[0] = *(char *)addr;
                     59:                                u.c[1] = *((char *)addr+1);
                     60:                                sum += u.s;
                     61:                                addr++;
                     62:                        } else
                     63:                                sum += *addr++;
                     64:                        ADDCARRY(sum);
                     65:                }
                     66:                if (len == -1)
                     67:                        /*
                     68:                         * Odd number of bytes. 
                     69:                         */
                     70:                        u.c[0] = *(u_char *)addr;
                     71:        }
                     72:        if (len == -1) {
                     73:                /* The last mbuf has odd # of bytes. Follow the
                     74:                   standard (the odd byte is shifted left by 8 bits) */
                     75:                u.c[1] = 0;
                     76:                sum += u.s;
                     77:                ADDCARRY(sum);
                     78:        }
                     79:        return (~sum & 0xffff);
                     80: }

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