Annotation of qemu/slirp/cksum.c, revision 1.1.1.3

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.
1.1.1.3 ! root       13:  * 3. Neither the name of the University nor the names of its contributors
1.1       root       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.
1.1.1.2   root       40:  *
1.1       root       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;
1.1.1.2   root       62: 
1.1       root       63:        if (m->m_len == 0)
                     64:           goto cont;
                     65:        w = mtod(m, u_int16_t *);
1.1.1.2   root       66: 
1.1       root       67:        mlen = m->m_len;
1.1.1.2   root       68: 
1.1       root       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:        }
1.1.1.2   root      106: 
1.1       root      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
1.1.1.2   root      116: 
1.1       root      117:                   mlen = -1;
                    118:        } else if (mlen == -1)
                    119:           s_util.c[0] = *(u_int8_t *)w;
1.1.1.2   root      120: 
1.1       root      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: }

unix.superglobalmegacorp.com