fletcher checksum function for OSPF LSA checksum.
refer to RFC1008.
Signed-off-by: Wataru ISHIDA <[email protected]>
---
ryu/lib/packet/packet_utils.py | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/ryu/lib/packet/packet_utils.py b/ryu/lib/packet/packet_utils.py
index 9331472..ad5ef66 100644
--- a/ryu/lib/packet/packet_utils.py
+++ b/ryu/lib/packet/packet_utils.py
@@ -97,3 +97,38 @@ def checksum_ip(ipvx, length, payload):
buf = header + payload
return checksum(buf)
+
+_MODX = 4102
+def fletcher_checksum(data, offset):
+ """
+ Fletcher Checksum -- Refer to RFC1008
+
+ calling with offset == _FLETCHER_CHECKSUM_VALIDATE will validate the
+ checksum without modifying the buffer; a valid checksum returns 0.
+ """
+ c0 = 0
+ c1 = 0
+ pos = 0
+ length = len(data)
+ data = bytearray(data)
+ data[offset:offset+2] = [0]*2
+
+ while pos < length:
+ tlen = min(length - pos, _MODX)
+ for d in data[pos:pos+tlen]:
+ c0 += d
+ c1 += c0
+ c0 %= 255
+ c1 %= 255
+ pos += tlen
+
+ x = ((length - offset - 1) * c0 - c1) % 255
+ if x <= 0:
+ x += 255
+ y = 510 - c0 - x
+ if y > 255:
+ y -= 255
+
+ data[offset] = x
+ data[offset+1] = y
+ return (x << 8) | (y & 0xff)
--
1.8.1.2
------------------------------------------------------------------------------
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