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Annotation of previous_trunk/src/slirp/cksum.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1988, 1992, 1993
        !             3:  *     The Regents of the University of California.  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. Neither the name of the University nor the names of its contributors
        !            14:  *    may be used to endorse or promote products derived from this software
        !            15:  *    without specific prior written permission.
        !            16:  *
        !            17:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            18:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            19:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            20:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            21:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            22:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            23:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            24:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            25:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            26:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            27:  * SUCH DAMAGE.
        !            28:  *
        !            29:  *     @(#)in_cksum.c  8.1 (Berkeley) 6/10/93
        !            30:  * in_cksum.c,v 1.2 1994/08/02 07:48:16 davidg Exp
        !            31:  */
        !            32: 
        !            33: #include <slirp.h>
        !            34: 
        !            35: /*
        !            36:  * Checksum routine for Internet Protocol family headers (Portable Version).
        !            37:  *
        !            38:  * This routine is very heavily used in the network
        !            39:  * code and should be modified for each CPU to be as fast as possible.
        !            40:  * 
        !            41:  * XXX Since we will never span more than 1 mbuf, we can optimise this
        !            42:  */
        !            43: 
        !            44: #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
        !            45: #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
        !            46: 
        !            47: int cksum(struct mbuf *m, int len)
        !            48: {
        !            49:        register u_int16_t *w;
        !            50:        register int sum = 0;
        !            51:        register int mlen = 0;
        !            52:        int byte_swapped = 0;
        !            53: 
        !            54:        union {
        !            55:                u_int8_t        c[2];
        !            56:                u_int16_t       s;
        !            57:        } s_util;
        !            58:        union {
        !            59:                u_int16_t s[2];
        !            60:                u_int32_t l;
        !            61:        } l_util;
        !            62:        
        !            63:        if (m->m_len == 0)
        !            64:           goto cont;
        !            65:        w = mtod(m, u_int16_t *);
        !            66:        
        !            67:        mlen = m->m_len;
        !            68:        
        !            69:        if (len < mlen)
        !            70:           mlen = len;
        !            71:        len -= mlen;
        !            72:        /*
        !            73:         * Force to even boundary.
        !            74:         */
        !            75:        if ((1 & (long) w) && (mlen > 0)) {
        !            76:                REDUCE;
        !            77:                sum <<= 8;
        !            78:                s_util.c[0] = *(u_int8_t *)w;
        !            79:                w = (u_int16_t *)((int8_t *)w + 1);
        !            80:                mlen--;
        !            81:                byte_swapped = 1;
        !            82:        }
        !            83:        /*
        !            84:         * Unroll the loop to make overhead from
        !            85:         * branches &c small.
        !            86:         */
        !            87:        while ((mlen -= 32) >= 0) {
        !            88:                sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
        !            89:                sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
        !            90:                sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
        !            91:                sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
        !            92:                w += 16;
        !            93:        }
        !            94:        mlen += 32;
        !            95:        while ((mlen -= 8) >= 0) {
        !            96:                sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
        !            97:                w += 4;
        !            98:        }
        !            99:        mlen += 8;
        !           100:        if (mlen == 0 && byte_swapped == 0)
        !           101:           goto cont;
        !           102:        REDUCE;
        !           103:        while ((mlen -= 2) >= 0) {
        !           104:                sum += *w++;
        !           105:        }
        !           106:        
        !           107:        if (byte_swapped) {
        !           108:                REDUCE;
        !           109:                sum <<= 8;
        !           110:                byte_swapped = 0;
        !           111:                if (mlen == -1) {
        !           112:                        s_util.c[1] = *(u_int8_t *)w;
        !           113:                        sum += s_util.s;
        !           114:                        mlen = 0;
        !           115:                } else
        !           116:                   
        !           117:                   mlen = -1;
        !           118:        } else if (mlen == -1)
        !           119:           s_util.c[0] = *(u_int8_t *)w;
        !           120:        
        !           121: cont:
        !           122: #ifdef DEBUG
        !           123:        if (len) {
        !           124:                DEBUG_ERROR((dfd, "cksum: out of data\n"));
        !           125:                DEBUG_ERROR((dfd, " len = %d\n", len));
        !           126:        }
        !           127: #endif
        !           128:        if (mlen == -1) {
        !           129:                /* The last mbuf has odd # of bytes. Follow the
        !           130:                 standard (the odd byte may be shifted left by 8 bits
        !           131:                           or not as determined by endian-ness of the machine) */
        !           132:                s_util.c[1] = 0;
        !           133:                sum += s_util.s;
        !           134:        }
        !           135:        REDUCE;
        !           136:        return (~sum & 0xffff);
        !           137: }

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