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

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