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;
+    }
+}
+