alg.go

Documentation: runtime

     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  package runtime
     6  
     7  import (
     8  	"internal/abi"
     9  	"internal/cpu"
    10  	"internal/goarch"
    11  	"unsafe"
    12  )
    13  
    14  const (
    15  	c0 = uintptr((8-goarch.PtrSize)/4*2860486313 + (goarch.PtrSize-4)/4*33054211828000289)
    16  	c1 = uintptr((8-goarch.PtrSize)/4*3267000013 + (goarch.PtrSize-4)/4*23344194077549503)
    17  )
    18  
    19  func memhash0(p unsafe.Pointer, h uintptr) uintptr {
    20  	return h
    21  }
    22  
    23  func memhash8(p unsafe.Pointer, h uintptr) uintptr {
    24  	return memhash(p, h, 1)
    25  }
    26  
    27  func memhash16(p unsafe.Pointer, h uintptr) uintptr {
    28  	return memhash(p, h, 2)
    29  }
    30  
    31  func memhash128(p unsafe.Pointer, h uintptr) uintptr {
    32  	return memhash(p, h, 16)
    33  }
    34  
    35  //go:nosplit
    36  func memhash_varlen(p unsafe.Pointer, h uintptr) uintptr {
    37  	ptr := getclosureptr()
    38  	size := *(*uintptr)(unsafe.Pointer(ptr + unsafe.Sizeof(h)))
    39  	return memhash(p, h, size)
    40  }
    41  
    42  // runtime variable to check if the processor we're running on
    43  // actually supports the instructions used by the AES-based
    44  // hash implementation.
    45  var useAeshash bool
    46  
    47  // in asm_*.s
    48  func memhash(p unsafe.Pointer, h, s uintptr) uintptr
    49  func memhash32(p unsafe.Pointer, h uintptr) uintptr
    50  func memhash64(p unsafe.Pointer, h uintptr) uintptr
    51  func strhash(p unsafe.Pointer, h uintptr) uintptr
    52  
    53  func strhashFallback(a unsafe.Pointer, h uintptr) uintptr {
    54  	x := (*stringStruct)(a)
    55  	return memhashFallback(x.str, h, uintptr(x.len))
    56  }
    57  
    58  // NOTE: Because NaN != NaN, a map can contain any
    59  // number of (mostly useless) entries keyed with NaNs.
    60  // To avoid long hash chains, we assign a random number
    61  // as the hash value for a NaN.
    62  
    63  func f32hash(p unsafe.Pointer, h uintptr) uintptr {
    64  	f := *(*float32)(p)
    65  	switch {
    66  	case f == 0:
    67  		return c1 * (c0 ^ h) // +0, -0
    68  	case f != f:
    69  		return c1 * (c0 ^ h ^ uintptr(rand())) // any kind of NaN
    70  	default:
    71  		return memhash(p, h, 4)
    72  	}
    73  }
    74  
    75  func f64hash(p unsafe.Pointer, h uintptr) uintptr {
    76  	f := *(*float64)(p)
    77  	switch {
    78  	case f == 0:
    79  		return c1 * (c0 ^ h) // +0, -0
    80  	case f != f:
    81  		return c1 * (c0 ^ h ^ uintptr(rand())) // any kind of NaN
    82  	default:
    83  		return memhash(p, h, 8)
    84  	}
    85  }
    86  
    87  func c64hash(p unsafe.Pointer, h uintptr) uintptr {
    88  	x := (*[2]float32)(p)
    89  	return f32hash(unsafe.Pointer(&x[1]), f32hash(unsafe.Pointer(&x[0]), h))
    90  }
    91  
    92  func c128hash(p unsafe.Pointer, h uintptr) uintptr {
    93  	x := (*[2]float64)(p)
    94  	return f64hash(unsafe.Pointer(&x[1]), f64hash(unsafe.Pointer(&x[0]), h))
    95  }
    96  
    97  func interhash(p unsafe.Pointer, h uintptr) uintptr {
    98  	a := (*iface)(p)
    99  	tab := a.tab
   100  	if tab == nil {
   101  		return h
   102  	}
   103  	t := tab._type
   104  	if t.Equal == nil {
   105  		// Check hashability here. We could do this check inside
   106  		// typehash, but we want to report the topmost type in
   107  		// the error text (e.g. in a struct with a field of slice type
   108  		// we want to report the struct, not the slice).
   109  		panic(errorString("hash of unhashable type " + toRType(t).string()))
   110  	}
   111  	if isDirectIface(t) {
   112  		return c1 * typehash(t, unsafe.Pointer(&a.data), h^c0)
   113  	} else {
   114  		return c1 * typehash(t, a.data, h^c0)
   115  	}
   116  }
   117  
   118  func nilinterhash(p unsafe.Pointer, h uintptr) uintptr {
   119  	a := (*eface)(p)
   120  	t := a._type
   121  	if t == nil {
   122  		return h
   123  	}
   124  	if t.Equal == nil {
   125  		// See comment in interhash above.
   126  		panic(errorString("hash of unhashable type " + toRType(t).string()))
   127  	}
   128  	if isDirectIface(t) {
   129  		return c1 * typehash(t, unsafe.Pointer(&a.data), h^c0)
   130  	} else {
   131  		return c1 * typehash(t, a.data, h^c0)
   132  	}
   133  }
   134  
   135  // typehash computes the hash of the object of type t at address p.
   136  // h is the seed.
   137  // This function is seldom used. Most maps use for hashing either
   138  // fixed functions (e.g. f32hash) or compiler-generated functions
   139  // (e.g. for a type like struct { x, y string }). This implementation
   140  // is slower but more general and is used for hashing interface types
   141  // (called from interhash or nilinterhash, above) or for hashing in
   142  // maps generated by reflect.MapOf (reflect_typehash, below).
   143  // Note: this function must match the compiler generated
   144  // functions exactly. See issue 37716.
   145  func typehash(t *_type, p unsafe.Pointer, h uintptr) uintptr {
   146  	if t.TFlag&abi.TFlagRegularMemory != 0 {
   147  		// Handle ptr sizes specially, see issue 37086.
   148  		switch t.Size_ {
   149  		case 4:
   150  			return memhash32(p, h)
   151  		case 8:
   152  			return memhash64(p, h)
   153  		default:
   154  			return memhash(p, h, t.Size_)
   155  		}
   156  	}
   157  	switch t.Kind_ & kindMask {
   158  	case kindFloat32:
   159  		return f32hash(p, h)
   160  	case kindFloat64:
   161  		return f64hash(p, h)
   162  	case kindComplex64:
   163  		return c64hash(p, h)
   164  	case kindComplex128:
   165  		return c128hash(p, h)
   166  	case kindString:
   167  		return strhash(p, h)
   168  	case kindInterface:
   169  		i := (*interfacetype)(unsafe.Pointer(t))
   170  		if len(i.Methods) == 0 {
   171  			return nilinterhash(p, h)
   172  		}
   173  		return interhash(p, h)
   174  	case kindArray:
   175  		a := (*arraytype)(unsafe.Pointer(t))
   176  		for i := uintptr(0); i < a.Len; i++ {
   177  			h = typehash(a.Elem, add(p, i*a.Elem.Size_), h)
   178  		}
   179  		return h
   180  	case kindStruct:
   181  		s := (*structtype)(unsafe.Pointer(t))
   182  		for _, f := range s.Fields {
   183  			if f.Name.IsBlank() {
   184  				continue
   185  			}
   186  			h = typehash(f.Typ, add(p, f.Offset), h)
   187  		}
   188  		return h
   189  	default:
   190  		// Should never happen, as typehash should only be called
   191  		// with comparable types.
   192  		panic(errorString("hash of unhashable type " + toRType(t).string()))
   193  	}
   194  }
   195  
   196  func mapKeyError(t *maptype, p unsafe.Pointer) error {
   197  	if !t.HashMightPanic() {
   198  		return nil
   199  	}
   200  	return mapKeyError2(t.Key, p)
   201  }
   202  
   203  func mapKeyError2(t *_type, p unsafe.Pointer) error {
   204  	if t.TFlag&abi.TFlagRegularMemory != 0 {
   205  		return nil
   206  	}
   207  	switch t.Kind_ & kindMask {
   208  	case kindFloat32, kindFloat64, kindComplex64, kindComplex128, kindString:
   209  		return nil
   210  	case kindInterface:
   211  		i := (*interfacetype)(unsafe.Pointer(t))
   212  		var t *_type
   213  		var pdata *unsafe.Pointer
   214  		if len(i.Methods) == 0 {
   215  			a := (*eface)(p)
   216  			t = a._type
   217  			if t == nil {
   218  				return nil
   219  			}
   220  			pdata = &a.data
   221  		} else {
   222  			a := (*iface)(p)
   223  			if a.tab == nil {
   224  				return nil
   225  			}
   226  			t = a.tab._type
   227  			pdata = &a.data
   228  		}
   229  
   230  		if t.Equal == nil {
   231  			return errorString("hash of unhashable type " + toRType(t).string())
   232  		}
   233  
   234  		if isDirectIface(t) {
   235  			return mapKeyError2(t, unsafe.Pointer(pdata))
   236  		} else {
   237  			return mapKeyError2(t, *pdata)
   238  		}
   239  	case kindArray:
   240  		a := (*arraytype)(unsafe.Pointer(t))
   241  		for i := uintptr(0); i < a.Len; i++ {
   242  			if err := mapKeyError2(a.Elem, add(p, i*a.Elem.Size_)); err != nil {
   243  				return err
   244  			}
   245  		}
   246  		return nil
   247  	case kindStruct:
   248  		s := (*structtype)(unsafe.Pointer(t))
   249  		for _, f := range s.Fields {
   250  			if f.Name.IsBlank() {
   251  				continue
   252  			}
   253  			if err := mapKeyError2(f.Typ, add(p, f.Offset)); err != nil {
   254  				return err
   255  			}
   256  		}
   257  		return nil
   258  	default:
   259  		// Should never happen, keep this case for robustness.
   260  		return errorString("hash of unhashable type " + toRType(t).string())
   261  	}
   262  }
   263  
   264  //go:linkname reflect_typehash reflect.typehash
   265  func reflect_typehash(t *_type, p unsafe.Pointer, h uintptr) uintptr {
   266  	return typehash(t, p, h)
   267  }
   268  
   269  func memequal0(p, q unsafe.Pointer) bool {
   270  	return true
   271  }
   272  func memequal8(p, q unsafe.Pointer) bool {
   273  	return *(*int8)(p) == *(*int8)(q)
   274  }
   275  func memequal16(p, q unsafe.Pointer) bool {
   276  	return *(*int16)(p) == *(*int16)(q)
   277  }
   278  func memequal32(p, q unsafe.Pointer) bool {
   279  	return *(*int32)(p) == *(*int32)(q)
   280  }
   281  func memequal64(p, q unsafe.Pointer) bool {
   282  	return *(*int64)(p) == *(*int64)(q)
   283  }
   284  func memequal128(p, q unsafe.Pointer) bool {
   285  	return *(*[2]int64)(p) == *(*[2]int64)(q)
   286  }
   287  func f32equal(p, q unsafe.Pointer) bool {
   288  	return *(*float32)(p) == *(*float32)(q)
   289  }
   290  func f64equal(p, q unsafe.Pointer) bool {
   291  	return *(*float64)(p) == *(*float64)(q)
   292  }
   293  func c64equal(p, q unsafe.Pointer) bool {
   294  	return *(*complex64)(p) == *(*complex64)(q)
   295  }
   296  func c128equal(p, q unsafe.Pointer) bool {
   297  	return *(*complex128)(p) == *(*complex128)(q)
   298  }
   299  func strequal(p, q unsafe.Pointer) bool {
   300  	return *(*string)(p) == *(*string)(q)
   301  }
   302  func interequal(p, q unsafe.Pointer) bool {
   303  	x := *(*iface)(p)
   304  	y := *(*iface)(q)
   305  	return x.tab == y.tab && ifaceeq(x.tab, x.data, y.data)
   306  }
   307  func nilinterequal(p, q unsafe.Pointer) bool {
   308  	x := *(*eface)(p)
   309  	y := *(*eface)(q)
   310  	return x._type == y._type && efaceeq(x._type, x.data, y.data)
   311  }
   312  func efaceeq(t *_type, x, y unsafe.Pointer) bool {
   313  	if t == nil {
   314  		return true
   315  	}
   316  	eq := t.Equal
   317  	if eq == nil {
   318  		panic(errorString("comparing uncomparable type " + toRType(t).string()))
   319  	}
   320  	if isDirectIface(t) {
   321  		// Direct interface types are ptr, chan, map, func, and single-element structs/arrays thereof.
   322  		// Maps and funcs are not comparable, so they can't reach here.
   323  		// Ptrs, chans, and single-element items can be compared directly using ==.
   324  		return x == y
   325  	}
   326  	return eq(x, y)
   327  }
   328  func ifaceeq(tab *itab, x, y unsafe.Pointer) bool {
   329  	if tab == nil {
   330  		return true
   331  	}
   332  	t := tab._type
   333  	eq := t.Equal
   334  	if eq == nil {
   335  		panic(errorString("comparing uncomparable type " + toRType(t).string()))
   336  	}
   337  	if isDirectIface(t) {
   338  		// See comment in efaceeq.
   339  		return x == y
   340  	}
   341  	return eq(x, y)
   342  }
   343  
   344  // Testing adapters for hash quality tests (see hash_test.go)
   345  func stringHash(s string, seed uintptr) uintptr {
   346  	return strhash(noescape(unsafe.Pointer(&s)), seed)
   347  }
   348  
   349  func bytesHash(b []byte, seed uintptr) uintptr {
   350  	s := (*slice)(unsafe.Pointer(&b))
   351  	return memhash(s.array, seed, uintptr(s.len))
   352  }
   353  
   354  func int32Hash(i uint32, seed uintptr) uintptr {
   355  	return memhash32(noescape(unsafe.Pointer(&i)), seed)
   356  }
   357  
   358  func int64Hash(i uint64, seed uintptr) uintptr {
   359  	return memhash64(noescape(unsafe.Pointer(&i)), seed)
   360  }
   361  
   362  func efaceHash(i any, seed uintptr) uintptr {
   363  	return nilinterhash(noescape(unsafe.Pointer(&i)), seed)
   364  }
   365  
   366  func ifaceHash(i interface {
   367  	F()
   368  }, seed uintptr) uintptr {
   369  	return interhash(noescape(unsafe.Pointer(&i)), seed)
   370  }
   371  
   372  const hashRandomBytes = goarch.PtrSize / 4 * 64
   373  
   374  // used in asm_{386,amd64,arm64}.s to seed the hash function
   375  var aeskeysched [hashRandomBytes]byte
   376  
   377  // used in hash{32,64}.go to seed the hash function
   378  var hashkey [4]uintptr
   379  
   380  func alginit() {
   381  	// Install AES hash algorithms if the instructions needed are present.
   382  	if (GOARCH == "386" || GOARCH == "amd64") &&
   383  		cpu.X86.HasAES && // AESENC
   384  		cpu.X86.HasSSSE3 && // PSHUFB
   385  		cpu.X86.HasSSE41 { // PINSR{D,Q}
   386  		initAlgAES()
   387  		return
   388  	}
   389  	if GOARCH == "arm64" && cpu.ARM64.HasAES {
   390  		initAlgAES()
   391  		return
   392  	}
   393  	for i := range hashkey {
   394  		hashkey[i] = uintptr(bootstrapRand()) | 1 // make sure these numbers are odd
   395  	}
   396  }
   397  
   398  func initAlgAES() {
   399  	useAeshash = true
   400  	// Initialize with random data so hash collisions will be hard to engineer.
   401  	key := (*[hashRandomBytes / 8]uint64)(unsafe.Pointer(&aeskeysched))
   402  	for i := range key {
   403  		key[i] = bootstrapRand()
   404  	}
   405  }
   406  
   407  // Note: These routines perform the read with a native endianness.
   408  func readUnaligned32(p unsafe.Pointer) uint32 {
   409  	q := (*[4]byte)(p)
   410  	if goarch.BigEndian {
   411  		return uint32(q[3]) | uint32(q[2])<<8 | uint32(q[1])<<16 | uint32(q[0])<<24
   412  	}
   413  	return uint32(q[0]) | uint32(q[1])<<8 | uint32(q[2])<<16 | uint32(q[3])<<24
   414  }
   415  
   416  func readUnaligned64(p unsafe.Pointer) uint64 {
   417  	q := (*[8]byte)(p)
   418  	if goarch.BigEndian {
   419  		return uint64(q[7]) | uint64(q[6])<<8 | uint64(q[5])<<16 | uint64(q[4])<<24 |
   420  			uint64(q[3])<<32 | uint64(q[2])<<40 | uint64(q[1])<<48 | uint64(q[0])<<56
   421  	}
   422  	return uint64(q[0]) | uint64(q[1])<<8 | uint64(q[2])<<16 | uint64(q[3])<<24 | uint64(q[4])<<32 | uint64(q[5])<<40 | uint64(q[6])<<48 | uint64(q[7])<<56
   423  }
   424
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