1 files changed, 35 insertions, 0 deletions
diff --git a/cksum.c b/cksum.c
new file mode 100644
index 0000000..b021533
--- /dev/null
+++ b/cksum.c
@@ -0,0 +1,35 @@
+/*
+
+(C) 2009-2011 Mika Ilmaranta <ilmis@nullnet.fi>
+
+License: GPLv2
+
+*/
+
+#include "cksum.h"
+
+int in_cksum(u_short *p, int n)
+{
+	register u_short answer;
+	register long sum = 0;
+	u_short odd_byte = 0;
+
+	while(n > 1) {
+		sum += *p++;
+		n -= 2;
+	}
+
+	/* mop up an odd byte, if necessary */
+	if(n == 1){
+		*(u_char*)(&odd_byte) = *(u_char*)p;
+		sum += odd_byte;
+	}
+
+	sum = (sum >> 16) + (sum & 0xffff);	/* add hi 16 to low 16 */
+	sum += (sum >> 16);			/* add carry */
+	answer = ~sum;				/* ones-complement, truncate */
+
+	return(answer);
+}
+
+/* EOF */