hash32.go

     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  // wyhash: https://github.com/wangyi-fudan/wyhash/blob/ceb019b530e2c1c14d70b79bfa2bc49de7d95bc1/Modern%20Non-Cryptographic%20Hash%20Function%20and%20Pseudorandom%20Number%20Generator.pdf
     7  
     8  //go:build 386 || arm || mips || mipsle
     9  
    10  package runtime
    11  
    12  import "unsafe"
    13  
    14  func memhash32Fallback(p unsafe.Pointer, seed uintptr) uintptr {
    15  	a, b := mix32(uint32(seed), uint32(4^hashkey[0]))
    16  	t := readUnaligned32(p)
    17  	a ^= t
    18  	b ^= t
    19  	a, b = mix32(a, b)
    20  	a, b = mix32(a, b)
    21  	return uintptr(a ^ b)
    22  }
    23  
    24  func memhash64Fallback(p unsafe.Pointer, seed uintptr) uintptr {
    25  	a, b := mix32(uint32(seed), uint32(8^hashkey[0]))
    26  	a ^= readUnaligned32(p)
    27  	b ^= readUnaligned32(add(p, 4))
    28  	a, b = mix32(a, b)
    29  	a, b = mix32(a, b)
    30  	return uintptr(a ^ b)
    31  }
    32  
    33  func memhashFallback(p unsafe.Pointer, seed, s uintptr) uintptr {
    34  
    35  	a, b := mix32(uint32(seed), uint32(s^hashkey[0]))
    36  	if s == 0 {
    37  		return uintptr(a ^ b)
    38  	}
    39  	for ; s > 8; s -= 8 {
    40  		a ^= readUnaligned32(p)
    41  		b ^= readUnaligned32(add(p, 4))
    42  		a, b = mix32(a, b)
    43  		p = add(p, 8)
    44  	}
    45  	if s >= 4 {
    46  		a ^= readUnaligned32(p)
    47  		b ^= readUnaligned32(add(p, s-4))
    48  	} else {
    49  		t := uint32(*(*byte)(p))
    50  		t |= uint32(*(*byte)(add(p, s>>1))) << 8
    51  		t |= uint32(*(*byte)(add(p, s-1))) << 16
    52  		b ^= t
    53  	}
    54  	a, b = mix32(a, b)
    55  	a, b = mix32(a, b)
    56  	return uintptr(a ^ b)
    57  }
    58  
    59  func mix32(a, b uint32) (uint32, uint32) {
    60  	c := uint64(a^uint32(hashkey[1])) * uint64(b^uint32(hashkey[2]))
    61  	return uint32(c), uint32(c >> 32)
    62  }
    63
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