This version avoids shifts, does as much native arithmetic as it

can, and then inner loop consequently runs 10 times faster than the straight
forward, but provably correct version.

SCCS-vsn: sys/netns/ns_cksum.c 1.2

diff --git a/usr/src/sys/netns/ns_cksum.c b/usr/src/sys/netns/ns_cksum.c
index bf612f6..46aa942 100644 (file)
--- a/usr/src/sys/netns/ns_cksum.c
+++ b/usr/src/sys/netns/ns_cksum.c
@@ -1,51 +1,168 @@
-/*     ns_cksum.c      1.1     86/01/23        */
-

 /*
 /*

- * ns_cksum.c - Xerox Internet Datagram protocol checksum
+ * Copyright (c) 1982, 1988 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted
+ * provided that this notice is preserved and that due credit is given
+ * to the University of California at Berkeley. The name of the University
+ * may not be used to endorse or promote products derived from this
+ * software without specific prior written permission. This software
+ * is provided ``as is'' without express or implied warranty.
+ *
+ *      @(#)ns_cksum.c 1.2 (Berkeley) %G%

  */
 #include "types.h"
 #include "mbuf.h"
 
 /*
  */
 #include "types.h"
 #include "mbuf.h"
 
 /*

- * Perform (slowly) the Xerox Internet checksum algorithm on a
- *     chain of mbufs.  This means we add all the 16-bits words,
- *     shifting the sum after each 16-bit add.  Ones-complement
- *     arithmetic is required, so we fold the carry bits after
- *     each 16-bit add as well.
- * If the result is the *no-checksum* value 0xffff, return zero instead.
+ * Checksum routine for Network Systems Protocol Packets.

  *
  *

- * Chris Torek <chris@maryland>
- * James O'Toole <james@maryland>
+ * This routine is very heavily used in the network
+ * code and should be modified for each CPU to be as fast as possible.

  */
  */

+
+#define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
+#define FOLD(x) {l_util.l = x; x = l_util.s[0] + l_util.s[1]; ADDCARRY(x);}
+

 u_short
 ns_cksum(m, len)
        register struct mbuf *m;
        register int len;
 {
 u_short
 ns_cksum(m, len)
        register struct mbuf *m;
        register int len;
 {

-       register int cksum = 0;
-       register int shift = 8;
-       register u_char *p;
-       register int mlen;
+       register u_short *w;
+       register int sum = 0;
+       register int mlen = 0;
+       register int sum2;
+
+       union {
+               u_short s[2];
+               long    l;
+       } l_util;

 
 

-       if (len & 1)
-               printf("ns_cksum: odd length\n");
-       while (m && len) {
-               p = mtod(m, u_char *);
-               mlen = m->m_len;
-               if ((len -= mlen) < 0)
-                       mlen += len, len = 0;
-               while (--mlen >= 0) {
-                       cksum += *p++ << shift;
-                       if ((shift = 8 - shift) != 0) {
-                               cksum <<= 1;
-                               cksum = (cksum & 0xffff) + (cksum >> 16);
-                       }
+       for (;m && len; m = m->m_next) {
+               if (m->m_len == 0)
+                       continue;
+               /*
+                * 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;
+                        * ones-complement add it into the checksum.
+                        */
+                       sum  += *(u_char *)w; /* Big-Endian, else << 8 */
+                       sum += sum;
+                       w = (u_short *)(1 + (char *)w);
+                       mlen = m->m_len - 1;
+                       len--;
+                       FOLD(sum);
+               } else
+                       mlen = m->m_len;
+               if (len < mlen)
+                       mlen = len;
+               len -= mlen;
+               /*
+                * We can do a 16 bit ones complement sum using
+                * 32 bit arithmetic registers for adding,
+                * with carries from the low added
+                * into the high (by normal carry-chaining)
+                * so long as we fold back before 16 carries have occured.
+                */
+               if (1 & (int) w)
+                       goto uuuuglyy;
+#ifndef TINY
+/* -DTINY reduces the size from 1250 to 550, but slows it down by 22% */
+               while ((mlen -= 32) >= 0) {
+                       sum += w[0]; sum += sum; sum += w[1]; sum += sum;
+                       sum += w[2]; sum += sum; sum += w[3]; sum += sum;
+                       sum += w[4]; sum += sum; sum += w[5]; sum += sum;
+                       sum += w[6]; sum += sum; sum += w[7]; sum += sum;
+                       FOLD(sum);
+                       sum += w[8]; sum += sum; sum += w[9]; sum += sum;
+                       sum += w[10]; sum += sum; sum += w[11]; sum += sum;
+                       sum += w[12]; sum += sum; sum += w[13]; sum += sum;
+                       sum += w[14]; sum += sum; sum += w[15]; sum += sum;
+                       FOLD(sum);
+                       w += 16;

                }
                }

-               m = m->m_next;
-       }
-#ifdef notdef
-       if (len)
-               printf("ns_cksum: out of data\n");
+               mlen += 32;
+#endif
+               while ((mlen -= 8) >= 0) {
+                       sum += w[0]; sum += sum; sum += w[1]; sum += sum;
+                       sum += w[2]; sum += sum; sum += w[3]; sum += sum;
+                       FOLD(sum);
+                       w += 4;
+               }
+               mlen += 8;
+               while ((mlen -= 2) >= 0) {
+                       sum += *w++; sum += sum;
+               }
+               goto commoncase;
+uuuuglyy:
+#define ww(n) (((char *)w)[n + n])
+#define vv(n) (((char *)w)[n + n + 1])
+/* Big-Endian; else reverse ww and vv */
+               sum2 = 0;
+#ifndef TINY
+               while ((mlen -= 32) >= 0) {
+                   sum += ww(0); sum += sum; sum += ww(1); sum += sum;
+                   sum += ww(2); sum += sum; sum += ww(3); sum += sum;
+                   sum += ww(4); sum += sum; sum += ww(5); sum += sum;
+                   sum += ww(6); sum += sum; sum += ww(7); sum += sum;
+                   FOLD(sum);
+                   sum += ww(8); sum += sum; sum += ww(9); sum += sum;
+                   sum += ww(10); sum += sum; sum += ww(11); sum += sum;
+                   sum += ww(12); sum += sum; sum += ww(13); sum += sum;
+                   sum += ww(14); sum += sum; sum += ww(15); sum += sum;
+                   FOLD(sum);
+                   sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
+                   sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
+                   sum2 += vv(4); sum2 += sum2; sum2 += vv(5); sum2 += sum2;
+                   sum2 += vv(6); sum2 += sum2; sum2 += vv(7); sum2 += sum2;
+                   FOLD(sum2);
+                   sum2 += vv(8); sum2 += sum2; sum2 += vv(9); sum2 += sum2;
+                   sum2 += vv(10); sum2 += sum2; sum2 += vv(11); sum2 += sum2;
+                   sum2 += vv(12); sum2 += sum2; sum2 += vv(13); sum2 += sum2;
+                   sum2 += vv(14); sum2 += sum2; sum2 += vv(15); sum2 += sum2;
+                   FOLD(sum2);
+                   w += 16;
+               }
+               mlen += 32;

 #endif
 #endif

-       return (cksum == 0xffff ? 0 : cksum);
+               while ((mlen -= 8) >= 0) {
+                   sum += ww(0); sum += sum; sum += ww(1); sum += sum;
+                   sum += ww(2); sum += sum; sum += ww(3); sum += sum;
+                   FOLD(sum);
+                   sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
+                   sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
+                   FOLD(sum2);
+                   w += 4;
+               }
+               mlen += 8;
+               while ((mlen -= 2) >= 0) {
+                       sum += ww(0); sum += sum;
+                       sum2 += vv(0); sum2 += sum2;
+                       w++;
+               }
+               sum += (sum2 << 8);
+commoncase:
+               if (mlen == -1) {
+                       sum += *(u_char *)w << 8; /* Big-Endian, else no << 8 */
+               }
+               FOLD(sum);
+       }
+       if (mlen == -1) {
+               /* We had an odd number of bytes to sum; assume a garbage
+                  byte of zero and clean up */
+               sum += sum;
+               FOLD(sum);
+       }
+       /*
+        * sum has already been kept to low sixteen bits.
+        * just examine result and exit.
+        */
+       if(sum==0xffff) sum = 0;
+       return (sum);

 }
 }