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package tun
import "encoding/binary"
// TODO: Explore SIMD and/or other assembly optimizations.
func checksumNoFold(b []byte, initial uint64) uint64 {
ac := initial
i := 0
n := len(b)
for n >= 4 {
ac += uint64(binary.BigEndian.Uint32(b[i : i+4]))
n -= 4
i += 4
}
for n >= 2 {
ac += uint64(binary.BigEndian.Uint16(b[i : i+2]))
n -= 2
i += 2
}
if n == 1 {
ac += uint64(b[i]) << 8
}
return ac
}
func checksum(b []byte, initial uint64) uint16 {
ac := checksumNoFold(b, initial)
ac = (ac >> 16) + (ac & 0xffff)
ac = (ac >> 16) + (ac & 0xffff)
ac = (ac >> 16) + (ac & 0xffff)
ac = (ac >> 16) + (ac & 0xffff)
return uint16(ac)
}
func pseudoHeaderChecksumNoFold(protocol uint8, srcAddr, dstAddr []byte, totalLen uint16) uint64 {
sum := checksumNoFold(srcAddr, 0)
sum = checksumNoFold(dstAddr, sum)
sum = checksumNoFold([]byte{0, protocol}, sum)
tmp := make([]byte, 2)
binary.BigEndian.PutUint16(tmp, totalLen)
return checksumNoFold(tmp, sum)
}
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