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Annotation of 43BSDTahoe/sys/tahoe/ns_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:  *     @(#)ns_cksum.c  7.3 (Berkeley) 6/29/88
        !            18:  */
        !            19: 
        !            20: #include "types.h"
        !            21: #include "mbuf.h"
        !            22: /*
        !            23:  * Checksum routine for Network Systems Protocol Packets (Big-Endian).
        !            24:  *
        !            25:  * This routine is very heavily used in the network
        !            26:  * code and should be modified for each CPU to be as fast as possible.
        !            27:  */
        !            28: 
        !            29: #define ADDCARRY(x)  { if ((x) > 65535) (x) -= 65535; }
        !            30: #define FOLD(x) {l_util.l = (x); (x) = l_util.s[0] + l_util.s[1]; ADDCARRY(x);}
        !            31: 
        !            32: u_short
        !            33: ns_cksum(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:        register int sum2;
        !            41: 
        !            42:        union {
        !            43:                u_short s[2];
        !            44:                long    l;
        !            45:        } l_util;
        !            46: 
        !            47:        for (;m && len; m = m->m_next) {
        !            48:                if (m->m_len == 0)
        !            49:                        continue;
        !            50:                /*
        !            51:                 * Each trip around loop adds in
        !            52:                 * word from one mbuf segment.
        !            53:                 */
        !            54:                w = mtod(m, u_short *);
        !            55:                if (mlen == -1) {
        !            56:                        /*
        !            57:                         * There is a byte left from the last segment;
        !            58:                         * ones-complement add it into the checksum.
        !            59:                         */
        !            60:                        sum  += *(u_char *)w; /* Big-Endian, else << 8 */
        !            61:                        sum += sum;
        !            62:                        w = (u_short *)(1 + (char *)w);
        !            63:                        mlen = m->m_len - 1;
        !            64:                        len--;
        !            65:                        FOLD(sum);
        !            66:                } else
        !            67:                        mlen = m->m_len;
        !            68:                if (len < mlen)
        !            69:                        mlen = len;
        !            70:                len -= mlen;
        !            71:                /*
        !            72:                 * We can do a 16 bit ones complement sum using
        !            73:                 * 32 bit arithmetic registers for adding,
        !            74:                 * with carries from the low added
        !            75:                 * into the high (by normal carry-chaining)
        !            76:                 * so long as we fold back before 16 carries have occured.
        !            77:                 */
        !            78:                if (1 & (int) w)
        !            79:                        goto uuuuglyy;
        !            80: #ifndef TINY
        !            81: /* -DTINY reduces the size from 1250 to 550, but slows it down by 22% */
        !            82:                while ((mlen -= 32) >= 0) {
        !            83:                        sum += w[0]; sum += sum; sum += w[1]; sum += sum;
        !            84:                        sum += w[2]; sum += sum; sum += w[3]; sum += sum;
        !            85:                        sum += w[4]; sum += sum; sum += w[5]; sum += sum;
        !            86:                        sum += w[6]; sum += sum; sum += w[7]; sum += sum;
        !            87:                        FOLD(sum);
        !            88:                        sum += w[8]; sum += sum; sum += w[9]; sum += sum;
        !            89:                        sum += w[10]; sum += sum; sum += w[11]; sum += sum;
        !            90:                        sum += w[12]; sum += sum; sum += w[13]; sum += sum;
        !            91:                        sum += w[14]; sum += sum; sum += w[15]; sum += sum;
        !            92:                        FOLD(sum);
        !            93:                        w += 16;
        !            94:                }
        !            95:                mlen += 32;
        !            96: #endif
        !            97:                while ((mlen -= 8) >= 0) {
        !            98:                        sum += w[0]; sum += sum; sum += w[1]; sum += sum;
        !            99:                        sum += w[2]; sum += sum; sum += w[3]; sum += sum;
        !           100:                        FOLD(sum);
        !           101:                        w += 4;
        !           102:                }
        !           103:                mlen += 8;
        !           104:                while ((mlen -= 2) >= 0) {
        !           105:                        sum += *w++; sum += sum;
        !           106:                }
        !           107:                goto commoncase;
        !           108: uuuuglyy:
        !           109: /* Big-Endian; else reverse ww and vv */
        !           110: #define ww(n) (((u_char *)w)[n + n + 1])
        !           111: #define vv(n) (((u_char *)w)[n + n])
        !           112:                sum2 = 0;
        !           113: #ifndef TINY
        !           114:                while ((mlen -= 32) >= 0) {
        !           115:                    sum += ww(0); sum += sum; sum += ww(1); sum += sum;
        !           116:                    sum += ww(2); sum += sum; sum += ww(3); sum += sum;
        !           117:                    sum += ww(4); sum += sum; sum += ww(5); sum += sum;
        !           118:                    sum += ww(6); sum += sum; sum += ww(7); sum += sum;
        !           119:                    FOLD(sum);
        !           120:                    sum += ww(8); sum += sum; sum += ww(9); sum += sum;
        !           121:                    sum += ww(10); sum += sum; sum += ww(11); sum += sum;
        !           122:                    sum += ww(12); sum += sum; sum += ww(13); sum += sum;
        !           123:                    sum += ww(14); sum += sum; sum += ww(15); sum += sum;
        !           124:                    FOLD(sum);
        !           125:                    sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
        !           126:                    sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
        !           127:                    sum2 += vv(4); sum2 += sum2; sum2 += vv(5); sum2 += sum2;
        !           128:                    sum2 += vv(6); sum2 += sum2; sum2 += vv(7); sum2 += sum2;
        !           129:                    FOLD(sum2);
        !           130:                    sum2 += vv(8); sum2 += sum2; sum2 += vv(9); sum2 += sum2;
        !           131:                    sum2 += vv(10); sum2 += sum2; sum2 += vv(11); sum2 += sum2;
        !           132:                    sum2 += vv(12); sum2 += sum2; sum2 += vv(13); sum2 += sum2;
        !           133:                    sum2 += vv(14); sum2 += sum2; sum2 += vv(15); sum2 += sum2;
        !           134:                    FOLD(sum2);
        !           135:                    w += 16;
        !           136:                }
        !           137:                mlen += 32;
        !           138: #endif
        !           139:                while ((mlen -= 8) >= 0) {
        !           140:                    sum += ww(0); sum += sum; sum += ww(1); sum += sum;
        !           141:                    sum += ww(2); sum += sum; sum += ww(3); sum += sum;
        !           142:                    FOLD(sum);
        !           143:                    sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
        !           144:                    sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
        !           145:                    FOLD(sum2);
        !           146:                    w += 4;
        !           147:                }
        !           148:                mlen += 8;
        !           149:                while ((mlen -= 2) >= 0) {
        !           150:                        sum += ww(0); sum += sum;
        !           151:                        sum2 += vv(0); sum2 += sum2;
        !           152:                        w++;
        !           153:                }
        !           154:                sum += (sum2 << 8);
        !           155: commoncase:
        !           156:                if (mlen == -1) {
        !           157:                        sum += *(u_char *)w << 8; /* Big-Endian, else no << 8 */
        !           158:                }
        !           159:                FOLD(sum);
        !           160:        }
        !           161:        if (mlen == -1) {
        !           162:                /* We had an odd number of bytes to sum; assume a garbage
        !           163:                   byte of zero and clean up */
        !           164:                sum += sum;
        !           165:                FOLD(sum);
        !           166:        }
        !           167:        /*
        !           168:         * sum has already been kept to low sixteen bits.
        !           169:         * just examine result and exit.
        !           170:         */
        !           171:        if(sum==0xffff) sum = 0;
        !           172:        return (sum);
        !           173: }

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