From e562180e6fc70e9f933b0bb081d5b69859d04327 Mon Sep 17 00:00:00 2001
From: patacongo <patacongo@42af7a65-404d-4744-a932-0658087f49c3>
Date: Mon, 16 Mar 2009 01:05:55 +0000
Subject: Better fix

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@1618 42af7a65-404d-4744-a932-0658087f49c3
---
 nuttx/net/uip/uip_icmpinput.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/nuttx/net/uip/uip_icmpinput.c b/nuttx/net/uip/uip_icmpinput.c
index f2edcbcb5..e9b7a9367 100644
--- a/nuttx/net/uip/uip_icmpinput.c
+++ b/nuttx/net/uip/uip_icmpinput.c
@@ -142,12 +142,29 @@ void uip_icmpinput(struct uip_driver_s *dev)
 
       /* Recalculate the ICMP checksum */
 
+#if 0
+      /* The slow way... sum over the ICMP message */
+
       picmp->icmpchksum = 0;
       picmp->icmpchksum = ~uip_icmpchksum(dev, (((uint16)picmp->len[0] << 8) | (uint16)picmp->len[1]) - UIP_IPH_LEN);
       if (picmp->icmpchksum == 0)
         {
           picmp->icmpchksum = 0xffff;
         }
+#else
+      /* The quick way -- Since only the type has changed, just adjust the
+       * checksum for the change of type
+       */
+
+      if( picmp->icmpchksum >= HTONS(0xffff - (ICMP_ECHO_REQUEST << 8)))
+        {
+          picmp->icmpchksum += HTONS(ICMP_ECHO_REQUEST << 8) + 1;
+        }
+      else
+        {
+          picmp->icmpchksum += HTONS(ICMP_ECHO_REQUEST << 8);
+        }
+#endif
 
       nvdbg("Outgoing ICMP packet length: %d (%d)\n",
             dev->d_len, (picmp->len[0] << 8) | picmp->len[1]);
-- 
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