4.2 distribution

[unix-history] / usr / src / sys / vax / vax / in_cksum.c

diff --git a/usr/src/sys/vax/vax/in_cksum.c b/usr/src/sys/vax/vax/in_cksum.c
index ecc7f14..168baa3 100644 (file)
--- a/usr/src/sys/vax/vax/in_cksum.c
+++ b/usr/src/sys/vax/vax/in_cksum.c
@@ -1,34 +1,38 @@
-/* in_cksum.c 1.6 81/10/28 */
+/*     in_cksum.c      6.1     83/07/29        */

 
 

-#include <sys/types.h>
-#include "../bbnnet/net.h"
-#include "../bbnnet/mbuf.h"
-#include "../bbnnet/count.h"
+#include "../h/types.h"
+#include "../h/mbuf.h"
+#include "../netinet/in.h"
+#include "../netinet/in_systm.h"

 
 /*
 
 /*

- * Network primitives; this file varies per-cpu,
- * and the code here is for VAX only.
+ * 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.

  */
 
  */
 

-/*
- * Checksum routine for TCP/IP headers.  This
- * is very heavily used in the network
- * code and should be rewritten for each CPU
- * to be as fast as possible.
- */
-cksum(m, len)
+in_cksum(m, len)

        register struct mbuf *m;
        register int len;
 {
        register struct mbuf *m;
        register int len;
 {

-       register long *l;               /* known to be r9 */
-       register int sum = 0;           /* known to be r8 */
-       register u_short *w;            /* known to be r7 */
+       register u_short *w;            /* on vax, known to be r9 */
+       register int sum = 0;           /* on vax, known to be r8 */

        register int mlen = 0;
        register int mlen = 0;

-COUNT(CKSUM);

 
        for (;;) {
 
        for (;;) {

-               w = (u_short *)((int)m + m->m_off);
+               /*
+                * Each trip around loop adds in
+                * word from one mbuf segment.
+                */
+               w = mtod(m, u_short *);

                if (mlen == -1) {
                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;
                        sum += *(u_char *)w << 8;
                        w = (u_short *)((char *)w + 1);
                        mlen = m->m_len - 1;


@@ -39,10 +43,34 @@ COUNT(CKSUM);
                if (len < mlen)
                        mlen = len;
                len -= mlen;
                if (len < mlen)
                        mlen = len;
                len -= mlen;

-               l = (long *)w;
+               /*
+                * 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) {
                while ((mlen -= 32) >= 0) {

-                       asm("clrl r0");         /* clears carry */

 #undef ADD
 #undef ADD

+                       asm("clrl r0");         /* clears carry */

 #define ADD            asm("adwc (r9)+,r8;");
                        ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
                        asm("adwc $0,r8");
 #define ADD            asm("adwc (r9)+,r8;");
                        ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
                        asm("adwc $0,r8");


@@ -54,15 +82,28 @@ COUNT(CKSUM);
                        asm("adwc $0,r8");
                }
                mlen += 8;
                        asm("adwc $0,r8");
                }
                mlen += 8;

-               sum = ((sum >> 16) & 0xffff) + (sum & 0xffff);
-               w = (u_short *)l;
+               /*
+                * 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) {
                while ((mlen -= 2) >= 0) {

-                       asm("movzwl (r7)+,r0; addl2 r0,r8");
+                       asm("movzwl (r9)+,r0; addl2 r0,r8");

                }
                }

-               if (mlen == -1)
+               if (mlen == -1) {

                        sum += *(u_char *)w;
                        sum += *(u_char *)w;

+               }

                if (len == 0)
                        break;
                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");
                for (;;) {
                        if (m == 0) {
                                printf("cksum: out of data\n");


@@ -74,7 +115,12 @@ COUNT(CKSUM);
                }
        }
 done:
                }
        }
 done:

-       /* add together high and low parts of sum and carry to get cksum */
+       /*
+        * 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);
        { asm("ashl $-16,r8,r0; addw2 r0,r8; adwc $0,r8");
          asm("mcoml r8,r8; movzwl r8,r8"); }
        return (sum);