github.com/noisysockets/netstack@v0.6.0/pkg/tcpip/hash/jenkins/jenkins.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package jenkins implements Jenkins's one_at_a_time, non-cryptographic hash
    16  // functions created by by Bob Jenkins.
    17  //
    18  // See https://en.wikipedia.org/wiki/Jenkins_hash_function#cite_note-dobbsx-1
    19  package jenkins
    20  
    21  import (
    22  	"hash"
    23  )
    24  
    25  // Sum32 represents Jenkins's one_at_a_time hash.
    26  //
    27  // Use the Sum32 type directly (as opposed to New32 below)
    28  // to avoid allocations.
    29  type Sum32 uint32
    30  
    31  // New32 returns a new 32-bit Jenkins's one_at_a_time hash.Hash.
    32  //
    33  // Its Sum method will lay the value out in big-endian byte order.
    34  func New32() hash.Hash32 {
    35  	var s Sum32
    36  	return &s
    37  }
    38  
    39  // Reset resets the hash to its initial state.
    40  func (s *Sum32) Reset() { *s = 0 }
    41  
    42  // Sum32 returns the hash value
    43  func (s *Sum32) Sum32() uint32 {
    44  	sCopy := *s
    45  
    46  	sCopy += sCopy << 3
    47  	sCopy ^= sCopy >> 11
    48  	sCopy += sCopy << 15
    49  
    50  	return uint32(sCopy)
    51  }
    52  
    53  // Write adds more data to the running hash.
    54  //
    55  // It never returns an error.
    56  func (s *Sum32) Write(data []byte) (int, error) {
    57  	sCopy := *s
    58  	for _, b := range data {
    59  		sCopy += Sum32(b)
    60  		sCopy += sCopy << 10
    61  		sCopy ^= sCopy >> 6
    62  	}
    63  	*s = sCopy
    64  	return len(data), nil
    65  }
    66  
    67  // Size returns the number of bytes Sum will return.
    68  func (s *Sum32) Size() int { return 4 }
    69  
    70  // BlockSize returns the hash's underlying block size.
    71  func (s *Sum32) BlockSize() int { return 1 }
    72  
    73  // Sum appends the current hash to in and returns the resulting slice.
    74  //
    75  // It does not change the underlying hash state.
    76  func (s *Sum32) Sum(in []byte) []byte {
    77  	v := s.Sum32()
    78  	return append(in, byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
    79  }