Create the alias library. This is currently only used by

ppp (or will be shortly).  Natd can now be updated to use
this library rather than carrying its own version of the code.

Submitted by:	Charles Mott <cmott@srv.net>

1 files changed, 135 insertions, 0 deletions

diff --git a/lib/libalias/alias_util.c b/lib/libalias/alias_util.c
new file mode 100644
index 0000000..e5906ca
--- /dev/null
+++ b/lib/libalias/alias_util.c
@@ -0,0 +1,135 @@
+/*
+    Alias_util.h contains general utilities used by other functions
+    in the packet aliasing module.  At the moment, there are functions
+    for computing IP header and TCP packet checksums.
+
+    The checksum routines are based upon example code in a Unix networking
+    text written by Stevens (sorry, I can't remember the title -- but
+    at least this is a good author).
+
+    Initial Version:  August, 1996  (cjm)
+
+    Version 1.7:  January 9, 1997
+         Added differential checksum update function.
+*/
+
+/*
+Note: the checksum routines assume that the actual checksum word has
+been zeroed out.  If the checksum workd is filled with the proper value,
+then these routines will give a result of zero (useful for testing
+purposes);
+*/
+    
+#include <sys/types.h>
+#include <netinet/in_systm.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+
+#include "alias_local.h"
+
+u_short
+InternetChecksum(u_short *ptr, int nbytes)
+{
+    int sum, oddbyte;
+
+    sum = 0;
+    while (nbytes > 1)
+    {
+        sum += *ptr++;
+        nbytes -= 2;
+    }
+    if (nbytes == 1)
+    {
+        oddbyte = 0;
+        *((u_char *) &oddbyte) = *(u_char *) ptr;
+        sum += oddbyte;
+    }
+    sum = (sum >> 16) + (sum & 0xffff);
+    sum += (sum >> 16);
+    return(~sum);
+}
+
+u_short
+IpChecksum(struct ip *pip)
+{
+    return( InternetChecksum((u_short *) pip, (pip->ip_hl << 2)) );
+
+}
+
+u_short 
+TcpChecksum(struct ip *pip)
+{
+    u_short *ptr;
+    struct tcphdr *tc;
+    int nhdr, ntcp, nbytes;
+    int sum, oddbyte;
+
+    nhdr = pip->ip_hl << 2;
+    ntcp = ntohs(pip->ip_len) - nhdr;
+
+    tc = (struct tcphdr *) ((char *) pip + nhdr);
+    ptr = (u_short *) tc;
+    
+/* Add up TCP header and data */
+    nbytes = ntcp;
+    sum = 0;
+    while (nbytes > 1)
+    {
+        sum += *ptr++;
+        nbytes -= 2;
+    }
+    if (nbytes == 1)
+    {
+        oddbyte = 0;
+        *((u_char *) &oddbyte) = *(u_char *) ptr;
+        sum += oddbyte;
+    }
+
+/* "Pseudo-header" data */
+    ptr = (u_short *) &(pip->ip_dst);
+    sum += *ptr++;
+    sum += *ptr;
+    ptr = (u_short *) &(pip->ip_src);
+    sum += *ptr++;
+    sum += *ptr;
+    sum += htons((u_short) ntcp);
+    sum += htons((u_short) pip->ip_p);
+
+/* Roll over carry bits */
+    sum = (sum >> 16) + (sum & 0xffff);
+    sum += (sum >> 16);
+
+/* Return checksum */
+    return((u_short) ~sum);
+}
+
+
+void
+DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
+{
+    int i;
+    int accumulate;
+
+    accumulate = *cksum;
+    for (i=0; i<n; i++)
+    {
+        accumulate -= *new++;
+        accumulate += *old++;
+    }
+
+    if (accumulate < 0)
+    {
+        accumulate = -accumulate;
+        accumulate = (accumulate >> 16) + (accumulate & 0xffff);
+        accumulate += accumulate >> 16;
+        *cksum = (u_short) ~accumulate;
+    }
+    else
+    {
+        accumulate = (accumulate >> 16) + (accumulate & 0xffff);
+        accumulate += accumulate >> 16;
+        *cksum = (u_short) accumulate;
+    }
+}
+