github.com/gidoBOSSftw5731/go/src@v0.0.0-20210226122457-d24b0edbf019/runtime/hash32.go (about)

     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  //go:build 386 || arm || mips || mipsle
    10  // +build 386 arm mips mipsle
    11  
    12  package runtime
    13  
    14  import "unsafe"
    15  
    16  const (
    17  	// Constants for multiplication: four random odd 32-bit numbers.
    18  	m1 = 3168982561
    19  	m2 = 3339683297
    20  	m3 = 832293441
    21  	m4 = 2336365089
    22  )
    23  
    24  func memhashFallback(p unsafe.Pointer, seed, s uintptr) uintptr {
    25  	h := uint32(seed + s*hashkey[0])
    26  tail:
    27  	switch {
    28  	case s == 0:
    29  	case s < 4:
    30  		h ^= uint32(*(*byte)(p))
    31  		h ^= uint32(*(*byte)(add(p, s>>1))) << 8
    32  		h ^= uint32(*(*byte)(add(p, s-1))) << 16
    33  		h = rotl_15(h*m1) * m2
    34  	case s == 4:
    35  		h ^= readUnaligned32(p)
    36  		h = rotl_15(h*m1) * m2
    37  	case s <= 8:
    38  		h ^= readUnaligned32(p)
    39  		h = rotl_15(h*m1) * m2
    40  		h ^= readUnaligned32(add(p, s-4))
    41  		h = rotl_15(h*m1) * m2
    42  	case s <= 16:
    43  		h ^= readUnaligned32(p)
    44  		h = rotl_15(h*m1) * m2
    45  		h ^= readUnaligned32(add(p, 4))
    46  		h = rotl_15(h*m1) * m2
    47  		h ^= readUnaligned32(add(p, s-8))
    48  		h = rotl_15(h*m1) * m2
    49  		h ^= readUnaligned32(add(p, s-4))
    50  		h = rotl_15(h*m1) * m2
    51  	default:
    52  		v1 := h
    53  		v2 := uint32(seed * hashkey[1])
    54  		v3 := uint32(seed * hashkey[2])
    55  		v4 := uint32(seed * hashkey[3])
    56  		for s >= 16 {
    57  			v1 ^= readUnaligned32(p)
    58  			v1 = rotl_15(v1*m1) * m2
    59  			p = add(p, 4)
    60  			v2 ^= readUnaligned32(p)
    61  			v2 = rotl_15(v2*m2) * m3
    62  			p = add(p, 4)
    63  			v3 ^= readUnaligned32(p)
    64  			v3 = rotl_15(v3*m3) * m4
    65  			p = add(p, 4)
    66  			v4 ^= readUnaligned32(p)
    67  			v4 = rotl_15(v4*m4) * m1
    68  			p = add(p, 4)
    69  			s -= 16
    70  		}
    71  		h = v1 ^ v2 ^ v3 ^ v4
    72  		goto tail
    73  	}
    74  	h ^= h >> 17
    75  	h *= m3
    76  	h ^= h >> 13
    77  	h *= m4
    78  	h ^= h >> 16
    79  	return uintptr(h)
    80  }
    81  
    82  func memhash32Fallback(p unsafe.Pointer, seed uintptr) uintptr {
    83  	h := uint32(seed + 4*hashkey[0])
    84  	h ^= readUnaligned32(p)
    85  	h = rotl_15(h*m1) * m2
    86  	h ^= h >> 17
    87  	h *= m3
    88  	h ^= h >> 13
    89  	h *= m4
    90  	h ^= h >> 16
    91  	return uintptr(h)
    92  }
    93  
    94  func memhash64Fallback(p unsafe.Pointer, seed uintptr) uintptr {
    95  	h := uint32(seed + 8*hashkey[0])
    96  	h ^= readUnaligned32(p)
    97  	h = rotl_15(h*m1) * m2
    98  	h ^= readUnaligned32(add(p, 4))
    99  	h = rotl_15(h*m1) * m2
   100  	h ^= h >> 17
   101  	h *= m3
   102  	h ^= h >> 13
   103  	h *= m4
   104  	h ^= h >> 16
   105  	return uintptr(h)
   106  }
   107  
   108  // Note: in order to get the compiler to issue rotl instructions, we
   109  // need to constant fold the shift amount by hand.
   110  // TODO: convince the compiler to issue rotl instructions after inlining.
   111  func rotl_15(x uint32) uint32 {
   112  	return (x << 15) | (x >> (32 - 15))
   113  }