github.com/vpnishe/netstack@v1.10.6/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  //
    20  package jenkins
    21  
    22  import (
    23  	"hash"
    24  )
    25  
    26  // Sum32 represents Jenkins's one_at_a_time hash.
    27  //
    28  // Use the Sum32 type directly (as opposed to New32 below)
    29  // to avoid allocations.
    30  type Sum32 uint32
    31  
    32  // New32 returns a new 32-bit Jenkins's one_at_a_time hash.Hash.
    33  //
    34  // Its Sum method will lay the value out in big-endian byte order.
    35  func New32() hash.Hash32 {
    36  	var s Sum32
    37  	return &s
    38  }
    39  
    40  // Reset resets the hash to its initial state.
    41  func (s *Sum32) Reset() { *s = 0 }
    42  
    43  // Sum32 returns the hash value
    44  func (s *Sum32) Sum32() uint32 {
    45  	hash := *s
    46  
    47  	hash += (hash << 3)
    48  	hash ^= hash >> 11
    49  	hash += hash << 15
    50  
    51  	return uint32(hash)
    52  }
    53  
    54  // Write adds more data to the running hash.
    55  //
    56  // It never returns an error.
    57  func (s *Sum32) Write(data []byte) (int, error) {
    58  	hash := *s
    59  	for _, b := range data {
    60  		hash += Sum32(b)
    61  		hash += hash << 10
    62  		hash ^= hash >> 6
    63  	}
    64  	*s = hash
    65  	return len(data), nil
    66  }
    67  
    68  // Size returns the number of bytes Sum will return.
    69  func (s *Sum32) Size() int { return 4 }
    70  
    71  // BlockSize returns the hash's underlying block size.
    72  func (s *Sum32) BlockSize() int { return 1 }
    73  
    74  // Sum appends the current hash to in and returns the resulting slice.
    75  //
    76  // It does not change the underlying hash state.
    77  func (s *Sum32) Sum(in []byte) []byte {
    78  	v := s.Sum32()
    79  	return append(in, byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
    80  }