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Annotation of 43BSDReno/sys/vax/ns_cksum.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1985, 1986 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:  *     @(#)ns_cksum.c  7.5 (Berkeley) 6/28/90
        !            21:  */
        !            22: 
        !            23: #include "param.h"
        !            24: #include "mbuf.h"
        !            25: 
        !            26: 
        !            27: /*
        !            28:  * Checksum routine for Network Systems Protocol Packets (VAX Version).
        !            29:  *
        !            30:  * This routine is very heavily used in the network
        !            31:  * code and should be modified for each CPU to be as fast as possible.
        !            32:  */
        !            33: 
        !            34: u_short
        !            35: ns_cksum(m, len)
        !            36:        register struct mbuf *m;
        !            37:        register int len;
        !            38: {
        !            39:        register u_short *w;            /* on vax, known to be r9 */
        !            40:        register int sum = 0;           /* on vax, known to be r8 */
        !            41:        register int low = 0;           /* on vax, known to be r7 */
        !            42:        register int mlen = low;        /* want 0, shuts lint up about low */
        !            43: 
        !            44:        for (;;) {
        !            45:                /*
        !            46:                 * Each trip around loop adds in
        !            47:                 * word from one mbuf segment.
        !            48:                 */
        !            49:                w = mtod(m, u_short *);
        !            50:                if (mlen == -1) {
        !            51:                        /*
        !            52:                         * There is a byte left from the last segment;
        !            53:                         * add it into the checksum.  Don't have to worry
        !            54:                         * about a carry-out here because we make sure
        !            55:                         * that high part of (32 bit) sum is small below.
        !            56:                         */
        !            57:                        sum += *(u_char *)w << 8;
        !            58:                        sum += sum;
        !            59:                        w = (u_short *)((char *)w + 1);
        !            60:                        mlen = m->m_len - 1;
        !            61:                        len--;
        !            62:                } else
        !            63:                        mlen = m->m_len;
        !            64:                m = m->m_next;
        !            65:                if (len < mlen)
        !            66:                        mlen = len;
        !            67:                len -= mlen;
        !            68:                /*
        !            69:                 * Force to long boundary so we do longword aligned
        !            70:                 * memory operations.  It is too hard to do byte
        !            71:                 * adjustment, do only word adjustment.
        !            72:                 */
        !            73:                if (((int)w&0x2) && mlen >= 2) {
        !            74:                        sum += *w++;
        !            75:                        sum += sum;
        !            76:                        mlen -= 2;
        !            77:                }
        !            78:                /*
        !            79:                 *
        !            80:                 * We can do a 16 bit ones complement sum using
        !            81:                 * 32 bit arithmetic registers for adding,
        !            82:                 * with carries from the low added
        !            83:                 * into the high (by normal carry-chaining)
        !            84:                 * so long as we fold back before 16 carries have occured.
        !            85:                 *
        !            86:                 */
        !            87:                while ((mlen -= 32) >= 0) {
        !            88:                        /*asm("bicpsw $1");              clears carry */
        !            89: #undef ADD
        !            90: #define ADD asm("movw (r9)+,r7")asm("addl2 r7,r8")asm("addl2 r8,r8")
        !            91: #define FOLD { asm("ashl $-16,r8,r0")asm(" addw2 r0,r8"); \
        !            92:                  asm("adwc $0,r8")asm(" movzwl r8,r8"); }
        !            93:                        FOLD;
        !            94:                        ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
        !            95:                        FOLD;
        !            96:                        ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
        !            97:                }
        !            98:                mlen += 32;
        !            99:                while ((mlen -= 8) >= 0) {
        !           100:                        /*asm("bicpsw $1");              clears carry */
        !           101:                        FOLD;
        !           102:                        ADD; ADD; ADD; ADD;
        !           103:                }
        !           104:                mlen += 8;
        !           105:                /*
        !           106:                 * Now eliminate the possibility of carry-out's by
        !           107:                 * folding back to a 16 bit number (adding high and
        !           108:                 * low parts together.)  Then mop up trailing words
        !           109:                 * and maybe an odd byte.
        !           110:                 */
        !           111:                FOLD;
        !           112:                while ((mlen -= 2) >= 0) {
        !           113:                        ADD;
        !           114:                }
        !           115:                if (mlen == -1) {
        !           116:                        sum += *(u_char *)w;
        !           117:                }
        !           118:                if (len == 0)
        !           119:                        break;
        !           120:                /*
        !           121:                 * Locate the next block with some data.
        !           122:                 * If there is a word split across a boundary we
        !           123:                 * will wrap to the top with mlen == -1 and
        !           124:                 * then add it in shifted appropriately.
        !           125:                 */
        !           126:                for (;;) {
        !           127:                        if (m == 0) {
        !           128:                                printf("idpcksum: out of data\n");
        !           129:                                goto done;
        !           130:                        }
        !           131:                        if (m->m_len)
        !           132:                                break;
        !           133:                        m = m->m_next;
        !           134:                }
        !           135:        }
        !           136: done:
        !           137:        /*
        !           138:         * Add together high and low parts of sum
        !           139:         * and carry to get cksum.
        !           140:         * Have to be careful to not drop the last
        !           141:         * carry here.
        !           142:         */
        !           143:        FOLD;
        !           144:        
        !           145:        if(sum==0xffff) sum = 0;
        !           146:        return (sum);
        !           147: }

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