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undo 1's complement of the checksum, add / subtract and then redo

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This commit is contained in:
Nico Schottelius 2019-07-17 15:17:06 +02:00
parent b4882159f1
commit 4286ad0832
1 changed files with 8 additions and 18 deletions
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26
p4src/actions_delta_checksum.p4
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@ -12,7 +12,6 @@ action v4sum() {
tmp = tmp + (bit<16>) hdr.ipv4.totalLen -20; // 16 bit
tmp = tmp + (bit<16>) hdr.ipv4.protocol; // 8 bit
tmp = ~tmp;
meta.v4sum = tmp;
}
@ -40,7 +39,6 @@ action v6sum() {
tmp = tmp + (bit<16>) hdr.ipv6.payload_length; // 16 bit
tmp = tmp + (bit<16>) hdr.ipv6.next_header; // 8 bit
tmp = ~tmp;
meta.v6sum = tmp;
}
@ -53,29 +51,21 @@ action delta_prepare()
action delta_udp_from_v4_to_v6()
{
delta_prepare();
hdr.udp.checksum = hdr.udp.checksum + meta.v6sum;
/* prevent negative wrap around that loses 1 */
if(meta.v4sum > hdr.udp.checksum) {
bit<16> tmp = 0xffff - meta.v4sum;
hdr.udp.checksum = hdr.udp.checksum + tmp;
} else {
hdr.udp.checksum = hdr.udp.checksum - meta.v4sum;
}
bit<16> tmp = ~hdr.udp.checksum;
tmp = tmp + meta.v6sum;
tmp = tmp - meta.v4sum;
hdr.udp.checksum = ~tmp;
}
action delta_tcp_from_v4_to_v6()
{
delta_prepare();
hdr.tcp.checksum = hdr.tcp.checksum + meta.v6sum;
/* prevent negative wrap around that loses 1 */
if(meta.v4sum > hdr.tcp.checksum) {
bit<16> tmp = 0xffff - meta.v4sum;
hdr.tcp.checksum = hdr.tcp.checksum + tmp;
} else {
hdr.tcp.checksum = hdr.tcp.checksum - meta.v4sum;
}
bit<16> tmp = ~hdr.tcp.checksum;
tmp = tmp + meta.v6sum;
tmp = tmp - meta.v4sum;
hdr.tcp.checksum = ~tmp;
}
action delta_ipv4_from_v6_to_v4()