netselect (0.3.ds1-25) csum.c

--- netselect-0.3.ds1.orig/csum.c
+++ netselect-0.3.ds1/csum.c
@@ -0,0 +1,33 @@
+/*
+    Copyright (c)  2006, 2007		Dmitry Butskoy
+					<buc@citadel.stu.neva.ru>
+    License:  GPL v2 or any later
+
+    See COPYING for the status of this software.
+*/
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <netinet/in.h>
+
+
+u_int16_t in_csum (const void *ptr, size_t len) {
+	const u_int16_t *p = (const u_int16_t *) ptr;
+	size_t nw = len / 2;
+	unsigned int sum = 0;
+	u_int16_t res;
+
+	while (nw--)  sum += *p++;
+
+	if (len & 0x1)
+	    sum += htons (*((unsigned char *) p) << 8);
+
+	sum = (sum >> 16) + (sum & 0xffff);
+	sum += (sum >> 16);
+
+	res = ~sum;
+	if (!res)  res = ~0;
+
+	return res;
+}
+