...
Run Format

Source file src/runtime/hash32.go

Documentation: runtime

  // Copyright 2014 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // Hashing algorithm inspired by
  //   xxhash: https://code.google.com/p/xxhash/
  // cityhash: https://code.google.com/p/cityhash/
  
  // +build 386 arm mips mipsle
  
  package runtime
  
  import "unsafe"
  
  const (
  	// Constants for multiplication: four random odd 32-bit numbers.
  	m1 = 3168982561
  	m2 = 3339683297
  	m3 = 832293441
  	m4 = 2336365089
  )
  
  func memhash(p unsafe.Pointer, seed, s uintptr) uintptr {
  	if GOARCH == "386" && GOOS != "nacl" && useAeshash {
  		return aeshash(p, seed, s)
  	}
  	h := uint32(seed + s*hashkey[0])
  tail:
  	switch {
  	case s == 0:
  	case s < 4:
  		h ^= uint32(*(*byte)(p))
  		h ^= uint32(*(*byte)(add(p, s>>1))) << 8
  		h ^= uint32(*(*byte)(add(p, s-1))) << 16
  		h = rotl_15(h*m1) * m2
  	case s == 4:
  		h ^= readUnaligned32(p)
  		h = rotl_15(h*m1) * m2
  	case s <= 8:
  		h ^= readUnaligned32(p)
  		h = rotl_15(h*m1) * m2
  		h ^= readUnaligned32(add(p, s-4))
  		h = rotl_15(h*m1) * m2
  	case s <= 16:
  		h ^= readUnaligned32(p)
  		h = rotl_15(h*m1) * m2
  		h ^= readUnaligned32(add(p, 4))
  		h = rotl_15(h*m1) * m2
  		h ^= readUnaligned32(add(p, s-8))
  		h = rotl_15(h*m1) * m2
  		h ^= readUnaligned32(add(p, s-4))
  		h = rotl_15(h*m1) * m2
  	default:
  		v1 := h
  		v2 := uint32(seed * hashkey[1])
  		v3 := uint32(seed * hashkey[2])
  		v4 := uint32(seed * hashkey[3])
  		for s >= 16 {
  			v1 ^= readUnaligned32(p)
  			v1 = rotl_15(v1*m1) * m2
  			p = add(p, 4)
  			v2 ^= readUnaligned32(p)
  			v2 = rotl_15(v2*m2) * m3
  			p = add(p, 4)
  			v3 ^= readUnaligned32(p)
  			v3 = rotl_15(v3*m3) * m4
  			p = add(p, 4)
  			v4 ^= readUnaligned32(p)
  			v4 = rotl_15(v4*m4) * m1
  			p = add(p, 4)
  			s -= 16
  		}
  		h = v1 ^ v2 ^ v3 ^ v4
  		goto tail
  	}
  	h ^= h >> 17
  	h *= m3
  	h ^= h >> 13
  	h *= m4
  	h ^= h >> 16
  	return uintptr(h)
  }
  
  // Note: in order to get the compiler to issue rotl instructions, we
  // need to constant fold the shift amount by hand.
  // TODO: convince the compiler to issue rotl instructions after inlining.
  func rotl_15(x uint32) uint32 {
  	return (x << 15) | (x >> (32 - 15))
  }
  

View as plain text