Source file src/runtime/alg.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.
  
  package runtime
  
  import (
  	"runtime/internal/sys"
  	"unsafe"
  )
  
  const (
  	c0 = uintptr((8-sys.PtrSize)/4*2860486313 + (sys.PtrSize-4)/4*33054211828000289)
  	c1 = uintptr((8-sys.PtrSize)/4*3267000013 + (sys.PtrSize-4)/4*23344194077549503)
  )
  
  // type algorithms - known to compiler
  const (
  	alg_NOEQ = iota
  	alg_MEM0
  	alg_MEM8
  	alg_MEM16
  	alg_MEM32
  	alg_MEM64
  	alg_MEM128
  	alg_STRING
  	alg_INTER
  	alg_NILINTER
  	alg_FLOAT32
  	alg_FLOAT64
  	alg_CPLX64
  	alg_CPLX128
  	alg_max
  )
  
  // typeAlg is also copied/used in reflect/type.go.
  // keep them in sync.
  type typeAlg struct {
  	// function for hashing objects of this type
  	// (ptr to object, seed) -> hash
  	hash func(unsafe.Pointer, uintptr) uintptr
  	// function for comparing objects of this type
  	// (ptr to object A, ptr to object B) -> ==?
  	equal func(unsafe.Pointer, unsafe.Pointer) bool
  }
  
  func memhash0(p unsafe.Pointer, h uintptr) uintptr {
  	return h
  }
  func memhash8(p unsafe.Pointer, h uintptr) uintptr {
  	return memhash(p, h, 1)
  }
  func memhash16(p unsafe.Pointer, h uintptr) uintptr {
  	return memhash(p, h, 2)
  }
  func memhash32(p unsafe.Pointer, h uintptr) uintptr {
  	return memhash(p, h, 4)
  }
  func memhash64(p unsafe.Pointer, h uintptr) uintptr {
  	return memhash(p, h, 8)
  }
  func memhash128(p unsafe.Pointer, h uintptr) uintptr {
  	return memhash(p, h, 16)
  }
  
  // memhash_varlen is defined in assembly because it needs access
  // to the closure. It appears here to provide an argument
  // signature for the assembly routine.
  func memhash_varlen(p unsafe.Pointer, h uintptr) uintptr
  
  var algarray = [alg_max]typeAlg{
  	alg_NOEQ:     {nil, nil},
  	alg_MEM0:     {memhash0, memequal0},
  	alg_MEM8:     {memhash8, memequal8},
  	alg_MEM16:    {memhash16, memequal16},
  	alg_MEM32:    {memhash32, memequal32},
  	alg_MEM64:    {memhash64, memequal64},
  	alg_MEM128:   {memhash128, memequal128},
  	alg_STRING:   {strhash, strequal},
  	alg_INTER:    {interhash, interequal},
  	alg_NILINTER: {nilinterhash, nilinterequal},
  	alg_FLOAT32:  {f32hash, f32equal},
  	alg_FLOAT64:  {f64hash, f64equal},
  	alg_CPLX64:   {c64hash, c64equal},
  	alg_CPLX128:  {c128hash, c128equal},
  }
  
  var useAeshash bool
  
  // in asm_*.s
  func aeshash(p unsafe.Pointer, h, s uintptr) uintptr
  func aeshash32(p unsafe.Pointer, h uintptr) uintptr
  func aeshash64(p unsafe.Pointer, h uintptr) uintptr
  func aeshashstr(p unsafe.Pointer, h uintptr) uintptr
  
  func strhash(a unsafe.Pointer, h uintptr) uintptr {
  	x := (*stringStruct)(a)
  	return memhash(x.str, h, uintptr(x.len))
  }
  
  // NOTE: Because NaN != NaN, a map can contain any
  // number of (mostly useless) entries keyed with NaNs.
  // To avoid long hash chains, we assign a random number
  // as the hash value for a NaN.
  
  func f32hash(p unsafe.Pointer, h uintptr) uintptr {
  	f := *(*float32)(p)
  	switch {
  	case f == 0:
  		return c1 * (c0 ^ h) // +0, -0
  	case f != f:
  		return c1 * (c0 ^ h ^ uintptr(fastrand())) // any kind of NaN
  	default:
  		return memhash(p, h, 4)
  	}
  }
  
  func f64hash(p unsafe.Pointer, h uintptr) uintptr {
  	f := *(*float64)(p)
  	switch {
  	case f == 0:
  		return c1 * (c0 ^ h) // +0, -0
  	case f != f:
  		return c1 * (c0 ^ h ^ uintptr(fastrand())) // any kind of NaN
  	default:
  		return memhash(p, h, 8)
  	}
  }
  
  func c64hash(p unsafe.Pointer, h uintptr) uintptr {
  	x := (*[2]float32)(p)
  	return f32hash(unsafe.Pointer(&x[1]), f32hash(unsafe.Pointer(&x[0]), h))
  }
  
  func c128hash(p unsafe.Pointer, h uintptr) uintptr {
  	x := (*[2]float64)(p)
  	return f64hash(unsafe.Pointer(&x[1]), f64hash(unsafe.Pointer(&x[0]), h))
  }
  
  func interhash(p unsafe.Pointer, h uintptr) uintptr {
  	a := (*iface)(p)
  	tab := a.tab
  	if tab == nil {
  		return h
  	}
  	t := tab._type
  	fn := t.alg.hash
  	if fn == nil {
  		panic(errorString("hash of unhashable type " + t.string()))
  	}
  	if isDirectIface(t) {
  		return c1 * fn(unsafe.Pointer(&a.data), h^c0)
  	} else {
  		return c1 * fn(a.data, h^c0)
  	}
  }
  
  func nilinterhash(p unsafe.Pointer, h uintptr) uintptr {
  	a := (*eface)(p)
  	t := a._type
  	if t == nil {
  		return h
  	}
  	fn := t.alg.hash
  	if fn == nil {
  		panic(errorString("hash of unhashable type " + t.string()))
  	}
  	if isDirectIface(t) {
  		return c1 * fn(unsafe.Pointer(&a.data), h^c0)
  	} else {
  		return c1 * fn(a.data, h^c0)
  	}
  }
  
  func memequal0(p, q unsafe.Pointer) bool {
  	return true
  }
  func memequal8(p, q unsafe.Pointer) bool {
  	return *(*int8)(p) == *(*int8)(q)
  }
  func memequal16(p, q unsafe.Pointer) bool {
  	return *(*int16)(p) == *(*int16)(q)
  }
  func memequal32(p, q unsafe.Pointer) bool {
  	return *(*int32)(p) == *(*int32)(q)
  }
  func memequal64(p, q unsafe.Pointer) bool {
  	return *(*int64)(p) == *(*int64)(q)
  }
  func memequal128(p, q unsafe.Pointer) bool {
  	return *(*[2]int64)(p) == *(*[2]int64)(q)
  }
  func f32equal(p, q unsafe.Pointer) bool {
  	return *(*float32)(p) == *(*float32)(q)
  }
  func f64equal(p, q unsafe.Pointer) bool {
  	return *(*float64)(p) == *(*float64)(q)
  }
  func c64equal(p, q unsafe.Pointer) bool {
  	return *(*complex64)(p) == *(*complex64)(q)
  }
  func c128equal(p, q unsafe.Pointer) bool {
  	return *(*complex128)(p) == *(*complex128)(q)
  }
  func strequal(p, q unsafe.Pointer) bool {
  	return *(*string)(p) == *(*string)(q)
  }
  func interequal(p, q unsafe.Pointer) bool {
  	return ifaceeq(*(*iface)(p), *(*iface)(q))
  }
  func nilinterequal(p, q unsafe.Pointer) bool {
  	return efaceeq(*(*eface)(p), *(*eface)(q))
  }
  func efaceeq(x, y eface) bool {
  	t := x._type
  	if t != y._type {
  		return false
  	}
  	if t == nil {
  		return true
  	}
  	eq := t.alg.equal
  	if eq == nil {
  		panic(errorString("comparing uncomparable type " + t.string()))
  	}
  	if isDirectIface(t) {
  		return eq(noescape(unsafe.Pointer(&x.data)), noescape(unsafe.Pointer(&y.data)))
  	}
  	return eq(x.data, y.data)
  }
  func ifaceeq(x, y iface) bool {
  	xtab := x.tab
  	if xtab != y.tab {
  		return false
  	}
  	if xtab == nil {
  		return true
  	}
  	t := xtab._type
  	eq := t.alg.equal
  	if eq == nil {
  		panic(errorString("comparing uncomparable type " + t.string()))
  	}
  	if isDirectIface(t) {
  		return eq(noescape(unsafe.Pointer(&x.data)), noescape(unsafe.Pointer(&y.data)))
  	}
  	return eq(x.data, y.data)
  }
  
  // Testing adapters for hash quality tests (see hash_test.go)
  func stringHash(s string, seed uintptr) uintptr {
  	return algarray[alg_STRING].hash(noescape(unsafe.Pointer(&s)), seed)
  }
  
  func bytesHash(b []byte, seed uintptr) uintptr {
  	s := (*slice)(unsafe.Pointer(&b))
  	return memhash(s.array, seed, uintptr(s.len))
  }
  
  func int32Hash(i uint32, seed uintptr) uintptr {
  	return algarray[alg_MEM32].hash(noescape(unsafe.Pointer(&i)), seed)
  }
  
  func int64Hash(i uint64, seed uintptr) uintptr {
  	return algarray[alg_MEM64].hash(noescape(unsafe.Pointer(&i)), seed)
  }
  
  func efaceHash(i interface{}, seed uintptr) uintptr {
  	return algarray[alg_NILINTER].hash(noescape(unsafe.Pointer(&i)), seed)
  }
  
  func ifaceHash(i interface {
  	F()
  }, seed uintptr) uintptr {
  	return algarray[alg_INTER].hash(noescape(unsafe.Pointer(&i)), seed)
  }
  
  const hashRandomBytes = sys.PtrSize / 4 * 64
  
  // used in asm_{386,amd64}.s to seed the hash function
  var aeskeysched [hashRandomBytes]byte
  
  // used in hash{32,64}.go to seed the hash function
  var hashkey [4]uintptr
  
  func alginit() {
  	// Install aes hash algorithm if we have the instructions we need
  	if (GOARCH == "386" || GOARCH == "amd64") &&
  		GOOS != "nacl" &&
  		cpuid_ecx&(1<<25) != 0 && // aes (aesenc)
  		cpuid_ecx&(1<<9) != 0 && // sse3 (pshufb)
  		cpuid_ecx&(1<<19) != 0 { // sse4.1 (pinsr{d,q})
  		useAeshash = true
  		algarray[alg_MEM32].hash = aeshash32
  		algarray[alg_MEM64].hash = aeshash64
  		algarray[alg_STRING].hash = aeshashstr
  		// Initialize with random data so hash collisions will be hard to engineer.
  		getRandomData(aeskeysched[:])
  		return
  	}
  	getRandomData((*[len(hashkey) * sys.PtrSize]byte)(unsafe.Pointer(&hashkey))[:])
  	hashkey[0] |= 1 // make sure these numbers are odd
  	hashkey[1] |= 1
  	hashkey[2] |= 1
  	hashkey[3] |= 1
  }
  

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