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Annotation of 3BSD/cmd/ucbmail/hash.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Hashing routines to salt away machines seen scanning
        !             3:  * networks paths that we don't know about.
        !             4:  */
        !             5: 
        !             6: #define        XHSIZE          19              /* Size of extra hash table */
        !             7: #define        NXMID           (XHSIZE*3/4)    /* Max extra machines */
        !             8: 
        !             9: struct xtrahash {
        !            10:        char    *xh_name;               /* Name of machine */
        !            11:        short   xh_mid;                 /* Machine ID */
        !            12:        short   xh_attnet;              /* Attached networks */
        !            13: } xtrahash[XHSIZE];
        !            14: 
        !            15: struct xtrahash        *xtab[XHSIZE];          /* F: mid-->machine name */
        !            16: 
        !            17: short  midfree;                        /* Next free machine id */
        !            18: 
        !            19: /*
        !            20:  * Initialize the extra host hash table.
        !            21:  * Called by sreset.
        !            22:  */
        !            23: 
        !            24: minit()
        !            25: {
        !            26:        register struct xtrahash *xp, **tp;
        !            27:        register int i;
        !            28: 
        !            29:        midfree = 0;
        !            30:        tp = &xtab[0];
        !            31:        for (xp = &xtrahash[0]; xp < &xtrahash[XHSIZE]; xp++) {
        !            32:                xp->xh_name = NOSTR;
        !            33:                xp->xh_mid = 0;
        !            34:                xp->xh_attnet = 0;
        !            35:                *tp++ = (struct xtrahash *) 0;
        !            36:        }
        !            37: }
        !            38: 
        !            39: /*
        !            40:  * Stash a net name in the extra host hash table.
        !            41:  * If a new entry is put in the hash table, deduce what
        !            42:  * net the machine is attached to from the net character.
        !            43:  *
        !            44:  * If the machine is already known, add the given attached
        !            45:  * net to those already known.
        !            46:  */
        !            47: 
        !            48: mstash(name, attnet)
        !            49:        char name[];
        !            50: {
        !            51:        register struct xtrahash *xp;
        !            52:        struct xtrahash *xlocate();
        !            53: 
        !            54:        xp = xlocate(name);
        !            55:        if (xp == (struct xtrahash *) 0) {
        !            56:                printf("Ran out of machine id spots\n");
        !            57:                return(0);
        !            58:        }
        !            59:        if (xp->xh_name == NOSTR) {
        !            60:                if (midfree >= XHSIZE) {
        !            61:                        printf("Out of machine ids\n");
        !            62:                        return(0);
        !            63:                }
        !            64:                xtab[midfree] = xp;
        !            65:                xp->xh_name = savestr(name);
        !            66:                xp->xh_mid = 0200 + midfree++;
        !            67:        }
        !            68:        switch (attnet) {
        !            69:        case '!':
        !            70:        case '^':
        !            71:                xp->xh_attnet |= BN;
        !            72:                break;
        !            73: 
        !            74:        default:
        !            75:        case ':':
        !            76:                xp->xh_attnet |= SN;
        !            77:                break;
        !            78: 
        !            79:        case '@':
        !            80:                xp->xh_attnet |= AN;
        !            81:                break;
        !            82:        }
        !            83:        return(xp->xh_mid);
        !            84: }
        !            85: 
        !            86: /*
        !            87:  * Search for the given name in the hash table
        !            88:  * and return the pointer to it if found, or to the first
        !            89:  * empty slot if not found.
        !            90:  *
        !            91:  * If no free slots can be found, return 0.
        !            92:  */
        !            93: 
        !            94: struct xtrahash *
        !            95: xlocate(name)
        !            96:        char name[];
        !            97: {
        !            98:        register int h, q, i;
        !            99:        register char *cp;
        !           100:        register struct xtrahash *xp;
        !           101: 
        !           102:        for (h = 0, cp = name; *cp; h = (h << 2) + *cp++)
        !           103:                ;
        !           104:        if (h < 0 && (h = -h) < 0)
        !           105:                h = 0;
        !           106:        h = h % XHSIZE;
        !           107:        cp = name;
        !           108:        for (i = 0, q = 0; q < XHSIZE; i++, q = i * i) {
        !           109:                xp = &xtrahash[(h + q) % XHSIZE];
        !           110:                if (xp->xh_name == NOSTR)
        !           111:                        return(xp);
        !           112:                if (strcmp(cp, xp->xh_name) == 0)
        !           113:                        return(xp);
        !           114:                if (h - q < 0)
        !           115:                        q += XHSIZE;
        !           116:                xp = &xtrahash[(h - q) % XHSIZE];
        !           117:                if (xp->xh_name == NOSTR)
        !           118:                        return(xp);
        !           119:                if (strcmp(cp, xp->xh_name) == 0)
        !           120:                        return(xp);
        !           121:        }
        !           122:        return((struct xtrahash *) 0);
        !           123: }
        !           124: 
        !           125: /*
        !           126:  * Return the name from the extra host hash table corresponding
        !           127:  * to the passed machine id.
        !           128:  */
        !           129: 
        !           130: char *
        !           131: mlook(mid)
        !           132: {
        !           133:        register int m;
        !           134: 
        !           135:        if ((mid & 0200) == 0)
        !           136:                return(NOSTR);
        !           137:        m = mid & ~0200;
        !           138:        if (m >= midfree) {
        !           139:                printf("Use made of undefined machine id\n");
        !           140:                return(NOSTR);
        !           141:        }
        !           142:        return(xtrahash[xtab[m]].xh_name);
        !           143: }

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