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Annotation of 43BSDReno/sys/netinet/in_cksum.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1988 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution is only permitted until one year after the first shipment
        !             6:  * of 4.4BSD by the Regents.  Otherwise, redistribution and use in source and
        !             7:  * binary forms are permitted provided that: (1) source distributions retain
        !             8:  * this entire copyright notice and comment, and (2) distributions including
        !             9:  * binaries display the following acknowledgement:  This product includes
        !            10:  * software developed by the University of California, Berkeley and its
        !            11:  * contributors'' in the documentation or other materials provided with the
        !            12:  * distribution and in all advertising materials mentioning features or use
        !            13:  * of this software.  Neither the name of the University nor the names of
        !            14:  * its contributors may be used to endorse or promote products derived from
        !            15:  * this software without specific prior written permission.
        !            16:  * THIS SOFTWARE IS PROVIDED AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
        !            17:  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
        !            18:  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            19:  *
        !            20:  *     @(#)in_cksum.c  7.3 (Berkeley) 6/28/90
        !            21:  */
        !            22: 
        !            23: #include "../h/types.h"
        !            24: #include "../h/mbuf.h"
        !            25: 
        !            26: /*
        !            27:  * Checksum routine for Internet Protocol family headers (Portable Version).
        !            28:  *
        !            29:  * This routine is very heavily used in the network
        !            30:  * code and should be modified for each CPU to be as fast as possible.
        !            31:  */
        !            32: 
        !            33: #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
        !            34: #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
        !            35: 
        !            36: in_cksum_c(m, len)
        !            37:        register struct mbuf *m;
        !            38:        register int len;
        !            39: {
        !            40:        register u_short *w;
        !            41:        register int sum = 0;
        !            42:        register int mlen = 0;
        !            43:        int byte_swapped = 0;
        !            44: 
        !            45:        union {
        !            46:                char    c[2];
        !            47:                u_short s;
        !            48:        } s_util;
        !            49:        union {
        !            50:                u_short s[2];
        !            51:                long    l;
        !            52:        } l_util;
        !            53: 
        !            54:        for (;m && len; m = m->m_next) {
        !            55:                if (m->m_len == 0)
        !            56:                        continue;
        !            57:                w = mtod(m, u_short *);
        !            58:                if (mlen == -1) {
        !            59:                        /*
        !            60:                         * The first byte of this mbuf is the continuation
        !            61:                         * of a word spanning between this mbuf and the
        !            62:                         * last mbuf.
        !            63:                         *
        !            64:                         * s_util.c[0] is already saved when scanning previous 
        !            65:                         * mbuf.
        !            66:                         */
        !            67:                        s_util.c[1] = *(char *)w;
        !            68:                        sum += s_util.s;
        !            69:                        w = (u_short *)((char *)w + 1);
        !            70:                        mlen = m->m_len - 1;
        !            71:                        len--;
        !            72:                } else
        !            73:                        mlen = m->m_len;
        !            74:                if (len < mlen)
        !            75:                        mlen = len;
        !            76:                len -= mlen;
        !            77:                /*
        !            78:                 * Force to even boundary.
        !            79:                 */
        !            80:                if ((1 & (int) w) && (mlen > 0)) {
        !            81:                        REDUCE;
        !            82:                        sum <<= 8;
        !            83:                        s_util.c[0] = *(u_char *)w;
        !            84:                        w = (u_short *)((char *)w + 1);
        !            85:                        mlen--;
        !            86:                        byte_swapped = 1;
        !            87:                }
        !            88:                /*
        !            89:                 * Unroll the loop to make overhead from
        !            90:                 * branches &c small.
        !            91:                 */
        !            92:                while ((mlen -= 32) >= 0) {
        !            93:                        sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
        !            94:                        sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
        !            95:                        sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
        !            96:                        sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
        !            97:                        w += 16;
        !            98:                }
        !            99:                mlen += 32;
        !           100:                while ((mlen -= 8) >= 0) {
        !           101:                        sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
        !           102:                        w += 4;
        !           103:                }
        !           104:                mlen += 8;
        !           105:                if (mlen == 0 && byte_swapped == 0)
        !           106:                        continue;
        !           107:                REDUCE;
        !           108:                while ((mlen -= 2) >= 0) {
        !           109:                        sum += *w++;
        !           110:                }
        !           111:                if (byte_swapped) {
        !           112:                        REDUCE;
        !           113:                        sum <<= 8;
        !           114:                        byte_swapped = 0;
        !           115:                        if (mlen == -1) {
        !           116:                                s_util.c[1] = *(char *)w;
        !           117:                                sum += s_util.s;
        !           118:                                mlen = 0;
        !           119:                        } else
        !           120:                                mlen = -1;
        !           121:                } else if (mlen == -1)
        !           122:                        s_util.c[0] = *(char *)w;
        !           123:        }
        !           124:        if (len)
        !           125:                printf("cksum: out of data\n");
        !           126:        if (mlen == -1) {
        !           127:                /* The last mbuf has odd # of bytes. Follow the
        !           128:                   standard (the odd byte may be shifted left by 8 bits
        !           129:                   or not as determined by endian-ness of the machine) */
        !           130:                s_util.c[1] = 0;
        !           131:                sum += s_util.s;
        !           132:        }
        !           133:        REDUCE;
        !           134:        return (~sum & 0xffff);
        !           135: }

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