Return to in_cksum.c CVS log

Up to [CSRG BSD Unix] / 43BSDTahoe / sys / netinet

Annotation of 43BSDTahoe/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 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:  *     @(#)in_cksum.c  7.2 (Berkeley) 6/29/88
        !            18:  */
        !            19: 
        !            20: #include "../h/types.h"
        !            21: #include "../h/mbuf.h"
        !            22: 
        !            23: /*
        !            24:  * Checksum routine for Internet Protocol family headers (Portable Version).
        !            25:  *
        !            26:  * This routine is very heavily used in the network
        !            27:  * code and should be modified for each CPU to be as fast as possible.
        !            28:  */
        !            29: 
        !            30: #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
        !            31: #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
        !            32: 
        !            33: in_cksum_c(m, len)
        !            34:        register struct mbuf *m;
        !            35:        register int len;
        !            36: {
        !            37:        register u_short *w;
        !            38:        register int sum = 0;
        !            39:        register int mlen = 0;
        !            40:        int byte_swapped = 0;
        !            41: 
        !            42:        union {
        !            43:                char    c[2];
        !            44:                u_short s;
        !            45:        } s_util;
        !            46:        union {
        !            47:                u_short s[2];
        !            48:                long    l;
        !            49:        } l_util;
        !            50: 
        !            51:        for (;m && len; m = m->m_next) {
        !            52:                if (m->m_len == 0)
        !            53:                        continue;
        !            54:                w = mtod(m, u_short *);
        !            55:                if (mlen == -1) {
        !            56:                        /*
        !            57:                         * The first byte of this mbuf is the continuation
        !            58:                         * of a word spanning between this mbuf and the
        !            59:                         * last mbuf.
        !            60:                         *
        !            61:                         * s_util.c[0] is already saved when scanning previous 
        !            62:                         * mbuf.
        !            63:                         */
        !            64:                        s_util.c[1] = *(char *)w;
        !            65:                        sum += s_util.s;
        !            66:                        w = (u_short *)((char *)w + 1);
        !            67:                        mlen = m->m_len - 1;
        !            68:                        len--;
        !            69:                } else
        !            70:                        mlen = m->m_len;
        !            71:                if (len < mlen)
        !            72:                        mlen = len;
        !            73:                len -= mlen;
        !            74:                /*
        !            75:                 * Force to even boundary.
        !            76:                 */
        !            77:                if ((1 & (int) w) && (mlen > 0)) {
        !            78:                        REDUCE;
        !            79:                        sum <<= 8;
        !            80:                        s_util.c[0] = *(u_char *)w;
        !            81:                        w = (u_short *)((char *)w + 1);
        !            82:                        mlen--;
        !            83:                        byte_swapped = 1;
        !            84:                }
        !            85:                /*
        !            86:                 * Unroll the loop to make overhead from
        !            87:                 * branches &c small.
        !            88:                 */
        !            89:                while ((mlen -= 32) >= 0) {
        !            90:                        sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
        !            91:                        sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
        !            92:                        sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
        !            93:                        sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
        !            94:                        w += 16;
        !            95:                }
        !            96:                mlen += 32;
        !            97:                while ((mlen -= 8) >= 0) {
        !            98:                        sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
        !            99:                        w += 4;
        !           100:                }
        !           101:                mlen += 8;
        !           102:                if (mlen == 0 && byte_swapped == 0)
        !           103:                        continue;
        !           104:                REDUCE;
        !           105:                while ((mlen -= 2) >= 0) {
        !           106:                        sum += *w++;
        !           107:                }
        !           108:                if (byte_swapped) {
        !           109:                        REDUCE;
        !           110:                        sum <<= 8;
        !           111:                        byte_swapped = 0;
        !           112:                        if (mlen == -1) {
        !           113:                                s_util.c[1] = *(char *)w;
        !           114:                                sum += s_util.s;
        !           115:                                mlen = 0;
        !           116:                        } else
        !           117:                                mlen = -1;
        !           118:                } else if (mlen == -1)
        !           119:                        s_util.c[0] = *(char *)w;
        !           120:        }
        !           121:        if (len)
        !           122:                printf("cksum: out of data\n");
        !           123:        if (mlen == -1) {
        !           124:                /* The last mbuf has odd # of bytes. Follow the
        !           125:                   standard (the odd byte may be shifted left by 8 bits
        !           126:                   or not as determined by endian-ness of the machine) */
        !           127:                s_util.c[1] = 0;
        !           128:                sum += s_util.s;
        !           129:        }
        !           130:        REDUCE;
        !           131:        return (~sum & 0xffff);
        !           132: }

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.