...
Run Format

Source file src/hash/adler32/adler32.go

Documentation: hash/adler32

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // Package adler32 implements the Adler-32 checksum.
  //
  // It is defined in RFC 1950:
  //	Adler-32 is composed of two sums accumulated per byte: s1 is
  //	the sum of all bytes, s2 is the sum of all s1 values. Both sums
  //	are done modulo 65521. s1 is initialized to 1, s2 to zero.  The
  //	Adler-32 checksum is stored as s2*65536 + s1 in most-
  //	significant-byte first (network) order.
  package adler32
  
  import (
  	"errors"
  	"hash"
  )
  
  const (
  	// mod is the largest prime that is less than 65536.
  	mod = 65521
  	// nmax is the largest n such that
  	// 255 * n * (n+1) / 2 + (n+1) * (mod-1) <= 2^32-1.
  	// It is mentioned in RFC 1950 (search for "5552").
  	nmax = 5552
  )
  
  // The size of an Adler-32 checksum in bytes.
  const Size = 4
  
  // digest represents the partial evaluation of a checksum.
  // The low 16 bits are s1, the high 16 bits are s2.
  type digest uint32
  
  func (d *digest) Reset() { *d = 1 }
  
  // New returns a new hash.Hash32 computing the Adler-32 checksum. Its
  // Sum method will lay the value out in big-endian byte order. The
  // returned Hash32 also implements encoding.BinaryMarshaler and
  // encoding.BinaryUnmarshaler to marshal and unmarshal the internal
  // state of the hash.
  func New() hash.Hash32 {
  	d := new(digest)
  	d.Reset()
  	return d
  }
  
  func (d *digest) Size() int { return Size }
  
  func (d *digest) BlockSize() int { return 4 }
  
  const (
  	magic         = "adl\x01"
  	marshaledSize = len(magic) + 4
  )
  
  func (d *digest) MarshalBinary() ([]byte, error) {
  	b := make([]byte, 0, marshaledSize)
  	b = append(b, magic...)
  	b = appendUint32(b, uint32(*d))
  	return b, nil
  }
  
  func (d *digest) UnmarshalBinary(b []byte) error {
  	if len(b) < len(magic) || string(b[:len(magic)]) != magic {
  		return errors.New("hash/adler32: invalid hash state identifier")
  	}
  	if len(b) != marshaledSize {
  		return errors.New("hash/adler32: invalid hash state size")
  	}
  	*d = digest(readUint32(b[len(magic):]))
  	return nil
  }
  
  func appendUint32(b []byte, x uint32) []byte {
  	a := [4]byte{
  		byte(x >> 24),
  		byte(x >> 16),
  		byte(x >> 8),
  		byte(x),
  	}
  	return append(b, a[:]...)
  }
  
  func readUint32(b []byte) uint32 {
  	_ = b[3]
  	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
  }
  
  // Add p to the running checksum d.
  func update(d digest, p []byte) digest {
  	s1, s2 := uint32(d&0xffff), uint32(d>>16)
  	for len(p) > 0 {
  		var q []byte
  		if len(p) > nmax {
  			p, q = p[:nmax], p[nmax:]
  		}
  		for len(p) >= 4 {
  			s1 += uint32(p[0])
  			s2 += s1
  			s1 += uint32(p[1])
  			s2 += s1
  			s1 += uint32(p[2])
  			s2 += s1
  			s1 += uint32(p[3])
  			s2 += s1
  			p = p[4:]
  		}
  		for _, x := range p {
  			s1 += uint32(x)
  			s2 += s1
  		}
  		s1 %= mod
  		s2 %= mod
  		p = q
  	}
  	return digest(s2<<16 | s1)
  }
  
  func (d *digest) Write(p []byte) (nn int, err error) {
  	*d = update(*d, p)
  	return len(p), nil
  }
  
  func (d *digest) Sum32() uint32 { return uint32(*d) }
  
  func (d *digest) Sum(in []byte) []byte {
  	s := uint32(*d)
  	return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
  }
  
  // Checksum returns the Adler-32 checksum of data.
  func Checksum(data []byte) uint32 { return uint32(update(1, data)) }
  

View as plain text