github.com/spaolacci/murmur3@v1.1.0/murmur.go (about)

     1  // Copyright 2013, Sébastien Paolacci. 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  /*
     6  Package murmur3 implements Austin Appleby's non-cryptographic MurmurHash3.
     7  
     8   Reference implementation:
     9      http://code.google.com/p/smhasher/wiki/MurmurHash3
    10  
    11   History, characteristics and (legacy) perfs:
    12      https://sites.google.com/site/murmurhash/
    13      https://sites.google.com/site/murmurhash/statistics
    14  */
    15  package murmur3
    16  
    17  type bmixer interface {
    18  	bmix(p []byte) (tail []byte)
    19  	Size() (n int)
    20  	reset()
    21  }
    22  
    23  type digest struct {
    24  	clen int      // Digested input cumulative length.
    25  	tail []byte   // 0 to Size()-1 bytes view of `buf'.
    26  	buf  [16]byte // Expected (but not required) to be Size() large.
    27  	seed uint32   // Seed for initializing the hash.
    28  	bmixer
    29  }
    30  
    31  func (d *digest) BlockSize() int { return 1 }
    32  
    33  func (d *digest) Write(p []byte) (n int, err error) {
    34  	n = len(p)
    35  	d.clen += n
    36  
    37  	if len(d.tail) > 0 {
    38  		// Stick back pending bytes.
    39  		nfree := d.Size() - len(d.tail) // nfree ∈ [1, d.Size()-1].
    40  		if nfree < len(p) {
    41  			// One full block can be formed.
    42  			block := append(d.tail, p[:nfree]...)
    43  			p = p[nfree:]
    44  			_ = d.bmix(block) // No tail.
    45  		} else {
    46  			// Tail's buf is large enough to prevent reallocs.
    47  			p = append(d.tail, p...)
    48  		}
    49  	}
    50  
    51  	d.tail = d.bmix(p)
    52  
    53  	// Keep own copy of the 0 to Size()-1 pending bytes.
    54  	nn := copy(d.buf[:], d.tail)
    55  	d.tail = d.buf[:nn]
    56  
    57  	return n, nil
    58  }
    59  
    60  func (d *digest) Reset() {
    61  	d.clen = 0
    62  	d.tail = nil
    63  	d.bmixer.reset()
    64  }