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Annotation of 43BSDTahoe/sys/tahoe/in_cksum.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1982, 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  7.3 (Berkeley) 6/29/88
        !            18:  */
        !            19: 
        !            20: #include "types.h"
        !            21: #include "mbuf.h"
        !            22: 
        !            23: /*
        !            24:  * Checksum routine for Internet Protocol family headers (CCI 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)  { if ((x) > 65535) (x) -= 65535; }
        !            31: #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
        !            32: 
        !            33: #define ADD(n) asm("adwc n (r10),r9")
        !            34: #define MOP    asm("adwc $0,r9")
        !            35: #define BOTCH  asm("addl2 r7,r9")
        !            36: 
        !            37: in_cksum(m, len)
        !            38:        register struct mbuf *m;
        !            39:        register int len;
        !            40: {
        !            41:        register u_short *w;            /* On CCI, known to be r10 */
        !            42:        register int sum = 0;           /* On CCI, known to be r9 */
        !            43:        register int mlen = 0;
        !            44: #ifndef lint
        !            45:        register int ClearCarry = 0;    /* On CCI, known to be r7; see BOTCH */
        !            46: #endif
        !            47:        int byte_swapped = 0;
        !            48: 
        !            49:        union {
        !            50:                char    c[2];
        !            51:                u_short s;
        !            52:        } s_util;
        !            53:        union {
        !            54:                u_short s[2];
        !            55:                long    l;
        !            56:        } l_util;
        !            57: 
        !            58:        for (;m && len; m = m->m_next) {
        !            59:                if (m->m_len == 0)
        !            60:                        continue;
        !            61:                w = mtod(m, u_short *);
        !            62:                if (mlen == -1) {
        !            63:                        /*
        !            64:                         * The first byte of this mbuf is the continuation
        !            65:                         * of a word spanning between this mbuf and the
        !            66:                         * last mbuf.
        !            67:                         *
        !            68:                         * s_util.c[0] is already saved when scanning previous 
        !            69:                         * mbuf.  sum was REDUCEd when we found mlen == -1.
        !            70:                         */
        !            71:                        s_util.c[1] = *(char *)w;
        !            72:                        sum += s_util.s;
        !            73:                        w = (u_short *)((char *)w + 1);
        !            74:                        mlen = m->m_len - 1;
        !            75:                        len--;
        !            76:                } else
        !            77:                        mlen = m->m_len;
        !            78:                if (len < mlen)
        !            79:                        mlen = len;
        !            80:                len -= mlen;
        !            81:                /*
        !            82:                 * Force to long boundary so we do longword aligned
        !            83:                 * memory operations.
        !            84:                 */
        !            85:                if (3 & (int) w) {
        !            86:                        REDUCE;
        !            87:                        if ((1 & (int) w) && (mlen > 0)) {
        !            88:                                sum <<= 8;
        !            89:                                s_util.c[0] = *(char *)w;
        !            90:                                w = (u_short *)((char *)w + 1);
        !            91:                                mlen--;
        !            92:                                byte_swapped = 1;
        !            93:                        }
        !            94:                        if ((2 & (int) w) && (mlen >= 2)) {
        !            95:                                sum += *w++;
        !            96:                                mlen -= 2;
        !            97:                        }
        !            98:                }
        !            99:                /*
        !           100:                 * Do as much of the checksum as possible 32 bits at at time.
        !           101:                 * In fact, this loop is unrolled to make overhead from
        !           102:                 * branches &c small.
        !           103:                 */
        !           104:                while ((mlen -= 32) >= 0) {
        !           105:                        /*
        !           106:                         * The loop construct clears carry for us
        !           107:                         * on vaxen, however, on the CCI machine subtracting
        !           108:                         * a small postive number from a larger one doesn't.
        !           109:                         * 
        !           110:                         * Doing a bicpsw is very slow (slows down the routine
        !           111:                         * by a factor of 2); explicitly adding an immediate
        !           112:                         * 0 to a register is optimized out; so we fake out
        !           113:                         * the optimizer and add a register whose contents
        !           114:                         * is always zero.
        !           115:                         */
        !           116:                        BOTCH;
        !           117:                        ADD(0); ADD(4); ADD(8); ADD(12);
        !           118:                        ADD(16); ADD(20); ADD(24); ADD(28);
        !           119:                        MOP; w += 16;
        !           120:                }
        !           121:                mlen += 32;
        !           122:                while ((mlen -= 8) >= 0) {
        !           123:                        BOTCH;
        !           124:                        ADD(0); ADD(4);
        !           125:                        MOP;
        !           126:                        w += 4;
        !           127:                }
        !           128:                mlen += 8;
        !           129:                if (mlen == 0 && byte_swapped == 0)
        !           130:                        continue;       /* worth 1% maybe ?? */
        !           131:                REDUCE;
        !           132:                while ((mlen -= 2) >= 0) {
        !           133:                        sum += *w++;
        !           134:                }
        !           135:                if (byte_swapped) {
        !           136:                        sum <<= 8;
        !           137:                        byte_swapped = 0;
        !           138:                        if (mlen == -1) {
        !           139:                                s_util.c[1] = *(char *)w;
        !           140:                                sum += s_util.s;
        !           141:                                mlen = 0;
        !           142:                        } else
        !           143:                                mlen = -1;
        !           144:                } else if (mlen == -1)
        !           145:                        /*
        !           146:                         * This mbuf has odd number of bytes. 
        !           147:                         * There could be a word split betwen
        !           148:                         * this mbuf and the next mbuf.
        !           149:                         * Save the last byte (to prepend to next mbuf).
        !           150:                         */
        !           151:                        s_util.c[0] = *(char *)w;
        !           152:        }
        !           153:        if (len)
        !           154:                printf("cksum: out of data\n");
        !           155:        if (mlen == -1) {
        !           156:                /* The last mbuf has odd # of bytes. Follow the
        !           157:                   standard (the odd byte is shifted left by 8 bits) */
        !           158:                s_util.c[1] = 0;
        !           159:                sum += s_util.s;
        !           160:        }
        !           161:        REDUCE;
        !           162:        return (~sum & 0xffff);
        !           163: }

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