alg.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  package runtime
     6  
     7  import (
     8  	"internal/abi"
     9  	"internal/byteorder"
    10  	"internal/goarch"
    11  	"internal/runtime/maps"
    12  	"internal/runtime/sys"
    13  	"unsafe"
    14  )
    15  
    16  const (
    17  	// We use 32-bit hash on Wasm, see hash32.go.
    18  	hashSize = (1-goarch.IsWasm)*goarch.PtrSize + goarch.IsWasm*4
    19  	c0       = uintptr((8-hashSize)/4*2860486313 + (hashSize-4)/4*33054211828000289)
    20  	c1       = uintptr((8-hashSize)/4*3267000013 + (hashSize-4)/4*23344194077549503)
    21  )
    22  
    23  func trimHash(h uintptr) uintptr {
    24  	if goarch.IsWasm != 0 {
    25  		// On Wasm, we use 32-bit hash, despite that uintptr is 64-bit.
    26  		// memhash* always returns a uintptr with high 32-bit being 0
    27  		// (see hash32.go). We trim the hash in other places where we
    28  		// compute the hash manually, e.g. in interhash.
    29  		return uintptr(uint32(h))
    30  	}
    31  	return h
    32  }
    33  
    34  func memhash0(p unsafe.Pointer, h uintptr) uintptr {
    35  	return h
    36  }
    37  
    38  func memhash8(p unsafe.Pointer, h uintptr) uintptr {
    39  	return memhash(p, h, 1)
    40  }
    41  
    42  func memhash16(p unsafe.Pointer, h uintptr) uintptr {
    43  	return memhash(p, h, 2)
    44  }
    45  
    46  func memhash128(p unsafe.Pointer, h uintptr) uintptr {
    47  	return memhash(p, h, 16)
    48  }
    49  
    50  //go:nosplit
    51  func memhash_varlen(p unsafe.Pointer, h uintptr) uintptr {
    52  	ptr := sys.GetClosurePtr()
    53  	size := *(*uintptr)(unsafe.Pointer(ptr + unsafe.Sizeof(h)))
    54  	return memhash(p, h, size)
    55  }
    56  
    57  // This is simple wrappers.
    58  // It's better to use maps.MemHash functions directly,
    59  // but we have reflection code that still calls hashing from runtime via LookupRuntime,
    60  // so we have to try to minimize overhead of an extra call.
    61  // For this add nosplit for performance
    62  
    63  // memhash should be an internal detail,
    64  // but widely used packages access it using linkname.
    65  // Notable members of the hall of shame include:
    66  //   - github.com/aacfactory/fns
    67  //   - github.com/dgraph-io/ristretto
    68  //   - github.com/minio/simdjson-go
    69  //   - github.com/nbd-wtf/go-nostr
    70  //   - github.com/outcaste-io/ristretto
    71  //   - github.com/puzpuzpuz/xsync/v2
    72  //   - github.com/puzpuzpuz/xsync/v3
    73  //   - github.com/authzed/spicedb
    74  //   - github.com/pingcap/badger
    75  //
    76  // Do not remove or change the type signature.
    77  // See go.dev/issue/67401.
    78  //
    79  //go:nosplit
    80  //go:linkname memhash
    81  func memhash(p unsafe.Pointer, h, s uintptr) uintptr {
    82  	return maps.MemHash(p, h, s)
    83  }
    84  
    85  //go:nosplit
    86  func memhash64(p unsafe.Pointer, seed uintptr) uintptr {
    87  	return maps.MemHash64(p, seed)
    88  }
    89  
    90  //go:nosplit
    91  func memhash32(p unsafe.Pointer, seed uintptr) uintptr {
    92  	return maps.MemHash32(p, seed)
    93  }
    94  
    95  // strhash should be an internal detail,
    96  // but widely used packages access it using linkname.
    97  // Notable members of the hall of shame include:
    98  //   - github.com/aristanetworks/goarista
    99  //   - github.com/bytedance/sonic
   100  //   - github.com/bytedance/go-tagexpr/v2
   101  //   - github.com/cloudwego/dynamicgo
   102  //   - github.com/v2fly/v2ray-core/v5
   103  //
   104  // Do not remove or change the type signature.
   105  // See go.dev/issue/67401.
   106  //
   107  //go:linkname strhash
   108  func strhash(p unsafe.Pointer, h uintptr) uintptr {
   109  	return maps.StrHash(p, h)
   110  }
   111  
   112  // NOTE: Because NaN != NaN, a map can contain any
   113  // number of (mostly useless) entries keyed with NaNs.
   114  // To avoid long hash chains, we assign a random number
   115  // as the hash value for a NaN.
   116  
   117  func f32hash(p unsafe.Pointer, h uintptr) uintptr {
   118  	f := *(*float32)(p)
   119  	switch {
   120  	case f == 0:
   121  		return trimHash(c1 * (c0 ^ h)) // +0, -0
   122  	case f != f:
   123  		return trimHash(c1 * (c0 ^ h ^ uintptr(rand()))) // any kind of NaN
   124  	default:
   125  		return memhash(p, h, 4)
   126  	}
   127  }
   128  
   129  func f64hash(p unsafe.Pointer, h uintptr) uintptr {
   130  	f := *(*float64)(p)
   131  	switch {
   132  	case f == 0:
   133  		return trimHash(c1 * (c0 ^ h)) // +0, -0
   134  	case f != f:
   135  		return trimHash(c1 * (c0 ^ h ^ uintptr(rand()))) // any kind of NaN
   136  	default:
   137  		return memhash(p, h, 8)
   138  	}
   139  }
   140  
   141  func c64hash(p unsafe.Pointer, h uintptr) uintptr {
   142  	x := (*[2]float32)(p)
   143  	return f32hash(unsafe.Pointer(&x[1]), f32hash(unsafe.Pointer(&x[0]), h))
   144  }
   145  
   146  func c128hash(p unsafe.Pointer, h uintptr) uintptr {
   147  	x := (*[2]float64)(p)
   148  	return f64hash(unsafe.Pointer(&x[1]), f64hash(unsafe.Pointer(&x[0]), h))
   149  }
   150  
   151  func interhash(p unsafe.Pointer, h uintptr) uintptr {
   152  	a := (*iface)(p)
   153  	tab := a.tab
   154  	if tab == nil {
   155  		return h
   156  	}
   157  	t := tab.Type
   158  	if t.Equal == nil {
   159  		// Check hashability here. We could do this check inside
   160  		// typehash, but we want to report the topmost type in
   161  		// the error text (e.g. in a struct with a field of slice type
   162  		// we want to report the struct, not the slice).
   163  		panic(errorString("hash of unhashable type " + toRType(t).string()))
   164  	}
   165  	if t.IsDirectIface() {
   166  		return trimHash(c1 * typehash(t, unsafe.Pointer(&a.data), h^c0))
   167  	} else {
   168  		return trimHash(c1 * typehash(t, a.data, h^c0))
   169  	}
   170  }
   171  
   172  // nilinterhash should be an internal detail,
   173  // but widely used packages access it using linkname.
   174  // Notable members of the hall of shame include:
   175  //   - github.com/anacrolix/stm
   176  //   - github.com/aristanetworks/goarista
   177  //
   178  // Do not remove or change the type signature.
   179  // See go.dev/issue/67401.
   180  //
   181  //go:linkname nilinterhash
   182  func nilinterhash(p unsafe.Pointer, h uintptr) uintptr {
   183  	a := (*eface)(p)
   184  	t := a._type
   185  	if t == nil {
   186  		return h
   187  	}
   188  	if t.Equal == nil {
   189  		// See comment in interhash above.
   190  		panic(errorString("hash of unhashable type " + toRType(t).string()))
   191  	}
   192  	if t.IsDirectIface() {
   193  		return trimHash(c1 * typehash(t, unsafe.Pointer(&a.data), h^c0))
   194  	} else {
   195  		return trimHash(c1 * typehash(t, a.data, h^c0))
   196  	}
   197  }
   198  
   199  // typehash computes the hash of the object of type t at address p.
   200  // h is the seed.
   201  // This function is seldom used. Most maps use for hashing either
   202  // fixed functions (e.g. f32hash) or compiler-generated functions
   203  // (e.g. for a type like struct { x, y string }). This implementation
   204  // is slower but more general and is used for hashing interface types
   205  // (called from interhash or nilinterhash, above) or for hashing in
   206  // maps generated by reflect.MapOf (reflect_typehash, below).
   207  //
   208  // typehash should be an internal detail,
   209  // but widely used packages access it using linkname.
   210  // Notable members of the hall of shame include:
   211  //   - github.com/puzpuzpuz/xsync/v2
   212  //   - github.com/puzpuzpuz/xsync/v3
   213  //
   214  // Do not remove or change the type signature.
   215  // See go.dev/issue/67401.
   216  //
   217  //go:linkname typehash
   218  func typehash(t *_type, p unsafe.Pointer, h uintptr) uintptr {
   219  	if t.TFlag&abi.TFlagRegularMemory != 0 {
   220  		// Handle ptr sizes specially, see issue 37086.
   221  		switch t.Size_ {
   222  		case 4:
   223  			return memhash32(p, h)
   224  		case 8:
   225  			return memhash64(p, h)
   226  		default:
   227  			return memhash(p, h, t.Size_)
   228  		}
   229  	}
   230  	switch t.Kind() {
   231  	case abi.Float32:
   232  		return f32hash(p, h)
   233  	case abi.Float64:
   234  		return f64hash(p, h)
   235  	case abi.Complex64:
   236  		return c64hash(p, h)
   237  	case abi.Complex128:
   238  		return c128hash(p, h)
   239  	case abi.String:
   240  		return strhash(p, h)
   241  	case abi.Interface:
   242  		i := (*interfacetype)(unsafe.Pointer(t))
   243  		if len(i.Methods) == 0 {
   244  			return nilinterhash(p, h)
   245  		}
   246  		return interhash(p, h)
   247  	case abi.Array:
   248  		a := (*arraytype)(unsafe.Pointer(t))
   249  		for i := uintptr(0); i < a.Len; i++ {
   250  			h = typehash(a.Elem, add(p, i*a.Elem.Size_), h)
   251  		}
   252  		return h
   253  	case abi.Struct:
   254  		s := (*structtype)(unsafe.Pointer(t))
   255  		for _, f := range s.Fields {
   256  			if f.Name.IsBlank() {
   257  				continue
   258  			}
   259  			h = typehash(f.Typ, add(p, f.Offset), h)
   260  		}
   261  		return h
   262  	default:
   263  		// Should never happen, as typehash should only be called
   264  		// with comparable types.
   265  		panic(errorString("hash of unhashable type " + toRType(t).string()))
   266  	}
   267  }
   268  
   269  //go:linkname reflect_typehash reflect.typehash
   270  func reflect_typehash(t *_type, p unsafe.Pointer, h uintptr) uintptr {
   271  	return typehash(t, p, h)
   272  }
   273  
   274  func memequal0(p, q unsafe.Pointer) bool {
   275  	return true
   276  }
   277  func memequal8(p, q unsafe.Pointer) bool {
   278  	return *(*int8)(p) == *(*int8)(q)
   279  }
   280  func memequal16(p, q unsafe.Pointer) bool {
   281  	return *(*int16)(p) == *(*int16)(q)
   282  }
   283  func memequal32(p, q unsafe.Pointer) bool {
   284  	return *(*int32)(p) == *(*int32)(q)
   285  }
   286  func memequal64(p, q unsafe.Pointer) bool {
   287  	return *(*int64)(p) == *(*int64)(q)
   288  }
   289  func memequal128(p, q unsafe.Pointer) bool {
   290  	return *(*[2]int64)(p) == *(*[2]int64)(q)
   291  }
   292  func f32equal(p, q unsafe.Pointer) bool {
   293  	return *(*float32)(p) == *(*float32)(q)
   294  }
   295  func f64equal(p, q unsafe.Pointer) bool {
   296  	return *(*float64)(p) == *(*float64)(q)
   297  }
   298  func c64equal(p, q unsafe.Pointer) bool {
   299  	return *(*complex64)(p) == *(*complex64)(q)
   300  }
   301  func c128equal(p, q unsafe.Pointer) bool {
   302  	return *(*complex128)(p) == *(*complex128)(q)
   303  }
   304  func strequal(p, q unsafe.Pointer) bool {
   305  	return *(*string)(p) == *(*string)(q)
   306  }
   307  func interequal(p, q unsafe.Pointer) bool {
   308  	x := *(*iface)(p)
   309  	y := *(*iface)(q)
   310  	return x.tab == y.tab && ifaceeq(x.tab, x.data, y.data)
   311  }
   312  func nilinterequal(p, q unsafe.Pointer) bool {
   313  	x := *(*eface)(p)
   314  	y := *(*eface)(q)
   315  	return x._type == y._type && efaceeq(x._type, x.data, y.data)
   316  }
   317  func efaceeq(t *_type, x, y unsafe.Pointer) bool {
   318  	if t == nil {
   319  		return true
   320  	}
   321  	eq := t.Equal
   322  	if eq == nil {
   323  		panic(errorString("comparing uncomparable type " + toRType(t).string()))
   324  	}
   325  	if t.IsDirectIface() {
   326  		// Direct interface types are ptr, chan, map, func, and single-element structs/arrays thereof.
   327  		// Maps and funcs are not comparable, so they can't reach here.
   328  		// Ptrs, chans, and single-element items can be compared directly using ==.
   329  		return x == y
   330  	}
   331  	return eq(x, y)
   332  }
   333  func ifaceeq(tab *itab, x, y unsafe.Pointer) bool {
   334  	if tab == nil {
   335  		return true
   336  	}
   337  	t := tab.Type
   338  	eq := t.Equal
   339  	if eq == nil {
   340  		panic(errorString("comparing uncomparable type " + toRType(t).string()))
   341  	}
   342  	if t.IsDirectIface() {
   343  		// See comment in efaceeq.
   344  		return x == y
   345  	}
   346  	return eq(x, y)
   347  }
   348  
   349  // Testing adapters for hash quality tests (see hash_test.go)
   350  //
   351  // stringHash should be an internal detail,
   352  // but widely used packages access it using linkname.
   353  // Notable members of the hall of shame include:
   354  //   - github.com/k14s/starlark-go
   355  //
   356  // Do not remove or change the type signature.
   357  // See go.dev/issue/67401.
   358  //
   359  //go:linkname stringHash
   360  func stringHash(s string, seed uintptr) uintptr {
   361  	return strhash(noescape(unsafe.Pointer(&s)), seed)
   362  }
   363  
   364  func bytesHash(b []byte, seed uintptr) uintptr {
   365  	s := (*slice)(unsafe.Pointer(&b))
   366  	return memhash(s.array, seed, uintptr(s.len))
   367  }
   368  
   369  func int32Hash(i uint32, seed uintptr) uintptr {
   370  	return memhash32(noescape(unsafe.Pointer(&i)), seed)
   371  }
   372  
   373  func int64Hash(i uint64, seed uintptr) uintptr {
   374  	return memhash64(noescape(unsafe.Pointer(&i)), seed)
   375  }
   376  
   377  func efaceHash(i any, seed uintptr) uintptr {
   378  	return nilinterhash(noescape(unsafe.Pointer(&i)), seed)
   379  }
   380  
   381  func ifaceHash(i interface {
   382  	F()
   383  }, seed uintptr) uintptr {
   384  	return interhash(noescape(unsafe.Pointer(&i)), seed)
   385  }
   386  
   387  func readUnaligned64(p unsafe.Pointer) uint64 {
   388  	q := (*[8]byte)(p)
   389  	if goarch.BigEndian {
   390  		return byteorder.BEUint64(q[:])
   391  	}
   392  	return byteorder.LEUint64(q[:])
   393  }
   394
View as plain text