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Source file src/runtime/hash64.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	//   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	// Note: in order to get the compiler to issue rotl instructions, we
    85	// need to constant fold the shift amount by hand.
    86	// TODO: convince the compiler to issue rotl instructions after inlining.
    87	func rotl_31(x uint64) uint64 {
    88		return (x << 31) | (x >> (64 - 31))
    89	}
    90	

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