hash64.go

Documentation: runtime

     1  // Copyright 2014 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  // Hashing algorithm inspired by
     6  //   xxhash: https://code.google.com/p/xxhash/
     7  // cityhash: https://code.google.com/p/cityhash/
     8  
     9  // +build amd64 amd64p32 arm64 mips64 mips64le ppc64 ppc64le s390x
    10  
    11  package runtime
    12  
    13  import "unsafe"
    14  
    15  const (
    16  	// Constants for multiplication: four random odd 64-bit numbers.
    17  	m1 = 16877499708836156737
    18  	m2 = 2820277070424839065
    19  	m3 = 9497967016996688599
    20  	m4 = 15839092249703872147
    21  )
    22  
    23  func memhash(p unsafe.Pointer, seed, s uintptr) uintptr {
    24  	if GOARCH == "amd64" && GOOS != "nacl" && useAeshash {
    25  		return aeshash(p, seed, s)
    26  	}
    27  	h := uint64(seed + s*hashkey[0])
    28  tail:
    29  	switch {
    30  	case s == 0:
    31  	case s < 4:
    32  		h ^= uint64(*(*byte)(p))
    33  		h ^= uint64(*(*byte)(add(p, s>>1))) << 8
    34  		h ^= uint64(*(*byte)(add(p, s-1))) << 16
    35  		h = rotl_31(h*m1) * m2
    36  	case s <= 8:
    37  		h ^= uint64(readUnaligned32(p))
    38  		h ^= uint64(readUnaligned32(add(p, s-4))) << 32
    39  		h = rotl_31(h*m1) * m2
    40  	case s <= 16:
    41  		h ^= readUnaligned64(p)
    42  		h = rotl_31(h*m1) * m2
    43  		h ^= readUnaligned64(add(p, s-8))
    44  		h = rotl_31(h*m1) * m2
    45  	case s <= 32:
    46  		h ^= readUnaligned64(p)
    47  		h = rotl_31(h*m1) * m2
    48  		h ^= readUnaligned64(add(p, 8))
    49  		h = rotl_31(h*m1) * m2
    50  		h ^= readUnaligned64(add(p, s-16))
    51  		h = rotl_31(h*m1) * m2
    52  		h ^= readUnaligned64(add(p, s-8))
    53  		h = rotl_31(h*m1) * m2
    54  	default:
    55  		v1 := h
    56  		v2 := uint64(seed * hashkey[1])
    57  		v3 := uint64(seed * hashkey[2])
    58  		v4 := uint64(seed * hashkey[3])
    59  		for s >= 32 {
    60  			v1 ^= readUnaligned64(p)
    61  			v1 = rotl_31(v1*m1) * m2
    62  			p = add(p, 8)
    63  			v2 ^= readUnaligned64(p)
    64  			v2 = rotl_31(v2*m2) * m3
    65  			p = add(p, 8)
    66  			v3 ^= readUnaligned64(p)
    67  			v3 = rotl_31(v3*m3) * m4
    68  			p = add(p, 8)
    69  			v4 ^= readUnaligned64(p)
    70  			v4 = rotl_31(v4*m4) * m1
    71  			p = add(p, 8)
    72  			s -= 32
    73  		}
    74  		h = v1 ^ v2 ^ v3 ^ v4
    75  		goto tail
    76  	}
    77  
    78  	h ^= h >> 29
    79  	h *= m3
    80  	h ^= h >> 32
    81  	return uintptr(h)
    82  }
    83  
    84  func memhash32(p unsafe.Pointer, seed uintptr) uintptr {
    85  	h := uint64(seed + 4*hashkey[0])
    86  	v := uint64(readUnaligned32(p))
    87  	h ^= v
    88  	h ^= v << 32
    89  	h = rotl_31(h*m1) * m2
    90  	h ^= h >> 29
    91  	h *= m3
    92  	h ^= h >> 32
    93  	return uintptr(h)
    94  }
    95  
    96  func memhash64(p unsafe.Pointer, seed uintptr) uintptr {
    97  	h := uint64(seed + 8*hashkey[0])
    98  	h ^= uint64(readUnaligned32(p)) | uint64(readUnaligned32(add(p, 4)))<<32
    99  	h = rotl_31(h*m1) * m2
   100  	h ^= h >> 29
   101  	h *= m3
   102  	h ^= h >> 32
   103  	return uintptr(h)
   104  }
   105  
   106  // Note: in order to get the compiler to issue rotl instructions, we
   107  // need to constant fold the shift amount by hand.
   108  // TODO: convince the compiler to issue rotl instructions after inlining.
   109  func rotl_31(x uint64) uint64 {
   110  	return (x << 31) | (x >> (64 - 31))
   111  }
   112
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