github.com/twelsh-aw/go/src@v0.0.0-20230516233729-a56fe86a7c81/hash/adler32/adler32.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package adler32 implements the Adler-32 checksum.
     6  //
     7  // It is defined in RFC 1950:
     8  //
     9  //	Adler-32 is composed of two sums accumulated per byte: s1 is
    10  //	the sum of all bytes, s2 is the sum of all s1 values. Both sums
    11  //	are done modulo 65521. s1 is initialized to 1, s2 to zero.  The
    12  //	Adler-32 checksum is stored as s2*65536 + s1 in most-
    13  //	significant-byte first (network) order.
    14  package adler32
    15  
    16  import (
    17  	"errors"
    18  	"hash"
    19  )
    20  
    21  const (
    22  	// mod is the largest prime that is less than 65536.
    23  	mod = 65521
    24  	// nmax is the largest n such that
    25  	// 255 * n * (n+1) / 2 + (n+1) * (mod-1) <= 2^32-1.
    26  	// It is mentioned in RFC 1950 (search for "5552").
    27  	nmax = 5552
    28  )
    29  
    30  // The size of an Adler-32 checksum in bytes.
    31  const Size = 4
    32  
    33  // digest represents the partial evaluation of a checksum.
    34  // The low 16 bits are s1, the high 16 bits are s2.
    35  type digest uint32
    36  
    37  func (d *digest) Reset() { *d = 1 }
    38  
    39  // New returns a new hash.Hash32 computing the Adler-32 checksum. Its
    40  // Sum method will lay the value out in big-endian byte order. The
    41  // returned Hash32 also implements encoding.BinaryMarshaler and
    42  // encoding.BinaryUnmarshaler to marshal and unmarshal the internal
    43  // state of the hash.
    44  func New() hash.Hash32 {
    45  	d := new(digest)
    46  	d.Reset()
    47  	return d
    48  }
    49  
    50  func (d *digest) Size() int { return Size }
    51  
    52  func (d *digest) BlockSize() int { return 4 }
    53  
    54  const (
    55  	magic         = "adl\x01"
    56  	marshaledSize = len(magic) + 4
    57  )
    58  
    59  func (d *digest) MarshalBinary() ([]byte, error) {
    60  	b := make([]byte, 0, marshaledSize)
    61  	b = append(b, magic...)
    62  	b = appendUint32(b, uint32(*d))
    63  	return b, nil
    64  }
    65  
    66  func (d *digest) UnmarshalBinary(b []byte) error {
    67  	if len(b) < len(magic) || string(b[:len(magic)]) != magic {
    68  		return errors.New("hash/adler32: invalid hash state identifier")
    69  	}
    70  	if len(b) != marshaledSize {
    71  		return errors.New("hash/adler32: invalid hash state size")
    72  	}
    73  	*d = digest(readUint32(b[len(magic):]))
    74  	return nil
    75  }
    76  
    77  func appendUint32(b []byte, x uint32) []byte {
    78  	a := [4]byte{
    79  		byte(x >> 24),
    80  		byte(x >> 16),
    81  		byte(x >> 8),
    82  		byte(x),
    83  	}
    84  	return append(b, a[:]...)
    85  }
    86  
    87  func readUint32(b []byte) uint32 {
    88  	_ = b[3]
    89  	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
    90  }
    91  
    92  // Add p to the running checksum d.
    93  func update(d digest, p []byte) digest {
    94  	s1, s2 := uint32(d&0xffff), uint32(d>>16)
    95  	for len(p) > 0 {
    96  		var q []byte
    97  		if len(p) > nmax {
    98  			p, q = p[:nmax], p[nmax:]
    99  		}
   100  		for len(p) >= 4 {
   101  			s1 += uint32(p[0])
   102  			s2 += s1
   103  			s1 += uint32(p[1])
   104  			s2 += s1
   105  			s1 += uint32(p[2])
   106  			s2 += s1
   107  			s1 += uint32(p[3])
   108  			s2 += s1
   109  			p = p[4:]
   110  		}
   111  		for _, x := range p {
   112  			s1 += uint32(x)
   113  			s2 += s1
   114  		}
   115  		s1 %= mod
   116  		s2 %= mod
   117  		p = q
   118  	}
   119  	return digest(s2<<16 | s1)
   120  }
   121  
   122  func (d *digest) Write(p []byte) (nn int, err error) {
   123  	*d = update(*d, p)
   124  	return len(p), nil
   125  }
   126  
   127  func (d *digest) Sum32() uint32 { return uint32(*d) }
   128  
   129  func (d *digest) Sum(in []byte) []byte {
   130  	s := uint32(*d)
   131  	return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
   132  }
   133  
   134  // Checksum returns the Adler-32 checksum of data.
   135  func Checksum(data []byte) uint32 { return uint32(update(1, data)) }