usr/src/sys/vax/vax/in_cksum.c

/*
 * Copyright (c) 1982, 1986 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)in_cksum.c  7.6 (Berkeley) 12/16/90
 */

#include "sys/param.h"
#include "sys/mbuf.h"

/*
 * Checksum routine for Internet Protocol family headers (VAX Version).
 *
 * This routine is very heavily used in the network
 * code and should be modified for each CPU to be as fast as possible.
 */

in_cksum(m, len)
        register struct mbuf *m;
        register int len;
{
        register u_short *w;            /* on vax, known to be r9 */
        register int sum = 0;           /* on vax, known to be r8 */
        register int mlen = 0;

        for (;;) {
                /*
                 * Each trip around loop adds in
                 * word from one mbuf segment.
                 */
                w = mtod(m, u_short *);
                if (mlen == -1) {
                        /*
                         * There is a byte left from the last segment;
                         * add it into the checksum.  Don't have to worry
                         * about a carry-out here because we make sure
                         * that high part of (32 bit) sum is small below.
                         */
                        sum += *(u_char *)w << 8;
                        w = (u_short *)((char *)w + 1);
                        mlen = m->m_len - 1;
                        len--;
                } else
                        mlen = m->m_len;
                m = m->m_next;
                if (len < mlen)
                        mlen = len;
                len -= mlen;
                /*
                 * Force to long boundary so we do longword aligned
                 * memory operations.  It is too hard to do byte
                 * adjustment, do only word adjustment.
                 */
                if (((int)w&0x2) && mlen >= 2) {
                        sum += *w++;
                        mlen -= 2;
                }
                /*
                 * Do as much of the checksum as possible 32 bits at at time.
                 * In fact, this loop is unrolled to make overhead from
                 * branches &c small.
                 *
                 * We can do a 16 bit ones complement sum 32 bits at a time
                 * because the 32 bit register is acting as two 16 bit
                 * registers for adding, with carries from the low added
                 * into the high (by normal carry-chaining) and carries
                 * from the high carried into the low on the next word
                 * by use of the adwc instruction.  This lets us run
                 * this loop at almost memory speed.
                 *
                 * Here there is the danger of high order carry out, and
                 * we carefully use adwc.
                 */
                while ((mlen -= 32) >= 0) {
#undef ADD
#ifdef unneeded          /* The loop construct clears carry for us... */
                        asm("bicpsr $1");               /* clears carry */
#endif
#define ADD             asm("adwc (r9)+,r8;");
                        ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
                        asm("adwc $0,r8");
                }
                mlen += 32;
                while ((mlen -= 8) >= 0) {
#ifdef unneeded          /* The loop construct clears carry for us... */
                        asm("bicpsr $1");               /* clears carry */
#endif
                        ADD; ADD;
                        asm("adwc $0,r8");
                }
                mlen += 8;
                /*
                 * Now eliminate the possibility of carry-out's by
                 * folding back to a 16 bit number (adding high and
                 * low parts together.)  Then mop up trailing words
                 * and maybe an odd byte.
                 */
                { asm("ashl $-16,r8,r0; addw2 r0,r8");
                  asm("adwc $0,r8; movzwl r8,r8"); }
                while ((mlen -= 2) >= 0) {
                        asm("movzwl (r9)+,r0; addl2 r0,r8");
                }
                if (mlen == -1) {
                        sum += *(u_char *)w;
                }
                if (len == 0)
                        break;
                /*
                 * Locate the next block with some data.
                 * If there is a word split across a boundary we
                 * will wrap to the top with mlen == -1 and
                 * then add it in shifted appropriately.
                 */
                for (;;) {
                        if (m == 0) {
                                printf("cksum: out of data\n");
                                goto done;
                        }
                        if (m->m_len)
                                break;
                        m = m->m_next;
                }
        }
done:
        /*
         * Add together high and low parts of sum
         * and carry to get cksum.
         * Have to be careful to not drop the last
         * carry here.
         */
        { asm("ashl $-16,r8,r0; addw2 r0,r8; adwc $0,r8");
          asm("mcoml r8,r8; movzwl r8,r8"); }
        return (sum);
}