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  		for _, f := range s.fields {
	 182  			if f.name.isBlank() {
	 183  				continue
	 184  			}
	 185  			h = typehash(f.typ, add(p, f.offset()), h)
	 186  		}
	 187  		return h
	 188  	default:
	 189  		// Should never happen, as typehash should only be called
	 190  		// with comparable types.
	 191  		panic(errorString("hash of unhashable type " + t.string()))
	 192  	}
	 193  }
	 194  
	 195  //go:linkname reflect_typehash reflect.typehash
	 196  func reflect_typehash(t *_type, p unsafe.Pointer, h uintptr) uintptr {
	 197  	return typehash(t, p, h)
	 198  }
	 199  
	 200  func memequal0(p, q unsafe.Pointer) bool {
	 201  	return true
	 202  }
	 203  func memequal8(p, q unsafe.Pointer) bool {
	 204  	return *(*int8)(p) == *(*int8)(q)
	 205  }
	 206  func memequal16(p, q unsafe.Pointer) bool {
	 207  	return *(*int16)(p) == *(*int16)(q)
	 208  }
	 209  func memequal32(p, q unsafe.Pointer) bool {
	 210  	return *(*int32)(p) == *(*int32)(q)
	 211  }
	 212  func memequal64(p, q unsafe.Pointer) bool {
	 213  	return *(*int64)(p) == *(*int64)(q)
	 214  }
	 215  func memequal128(p, q unsafe.Pointer) bool {
	 216  	return *(*[2]int64)(p) == *(*[2]int64)(q)
	 217  }
	 218  func f32equal(p, q unsafe.Pointer) bool {
	 219  	return *(*float32)(p) == *(*float32)(q)
	 220  }
	 221  func f64equal(p, q unsafe.Pointer) bool {
	 222  	return *(*float64)(p) == *(*float64)(q)
	 223  }
	 224  func c64equal(p, q unsafe.Pointer) bool {
	 225  	return *(*complex64)(p) == *(*complex64)(q)
	 226  }
	 227  func c128equal(p, q unsafe.Pointer) bool {
	 228  	return *(*complex128)(p) == *(*complex128)(q)
	 229  }
	 230  func strequal(p, q unsafe.Pointer) bool {
	 231  	return *(*string)(p) == *(*string)(q)
	 232  }
	 233  func interequal(p, q unsafe.Pointer) bool {
	 234  	x := *(*iface)(p)
	 235  	y := *(*iface)(q)
	 236  	return x.tab == y.tab && ifaceeq(x.tab, x.data, y.data)
	 237  }
	 238  func nilinterequal(p, q unsafe.Pointer) bool {
	 239  	x := *(*eface)(p)
	 240  	y := *(*eface)(q)
	 241  	return x._type == y._type && efaceeq(x._type, x.data, y.data)
	 242  }
	 243  func efaceeq(t *_type, x, y unsafe.Pointer) bool {
	 244  	if t == nil {
	 245  		return true
	 246  	}
	 247  	eq := t.equal
	 248  	if eq == nil {
	 249  		panic(errorString("comparing uncomparable type " + t.string()))
	 250  	}
	 251  	if isDirectIface(t) {
	 252  		// Direct interface types are ptr, chan, map, func, and single-element structs/arrays thereof.
	 253  		// Maps and funcs are not comparable, so they can't reach here.
	 254  		// Ptrs, chans, and single-element items can be compared directly using ==.
	 255  		return x == y
	 256  	}
	 257  	return eq(x, y)
	 258  }
	 259  func ifaceeq(tab *itab, x, y unsafe.Pointer) bool {
	 260  	if tab == nil {
	 261  		return true
	 262  	}
	 263  	t := tab._type
	 264  	eq := t.equal
	 265  	if eq == nil {
	 266  		panic(errorString("comparing uncomparable type " + t.string()))
	 267  	}
	 268  	if isDirectIface(t) {
	 269  		// See comment in efaceeq.
	 270  		return x == y
	 271  	}
	 272  	return eq(x, y)
	 273  }
	 274  
	 275  // Testing adapters for hash quality tests (see hash_test.go)
	 276  func stringHash(s string, seed uintptr) uintptr {
	 277  	return strhash(noescape(unsafe.Pointer(&s)), seed)
	 278  }
	 279  
	 280  func bytesHash(b []byte, seed uintptr) uintptr {
	 281  	s := (*slice)(unsafe.Pointer(&b))
	 282  	return memhash(s.array, seed, uintptr(s.len))
	 283  }
	 284  
	 285  func int32Hash(i uint32, seed uintptr) uintptr {
	 286  	return memhash32(noescape(unsafe.Pointer(&i)), seed)
	 287  }
	 288  
	 289  func int64Hash(i uint64, seed uintptr) uintptr {
	 290  	return memhash64(noescape(unsafe.Pointer(&i)), seed)
	 291  }
	 292  
	 293  func efaceHash(i interface{}, seed uintptr) uintptr {
	 294  	return nilinterhash(noescape(unsafe.Pointer(&i)), seed)
	 295  }
	 296  
	 297  func ifaceHash(i interface {
	 298  	F()
	 299  }, seed uintptr) uintptr {
	 300  	return interhash(noescape(unsafe.Pointer(&i)), seed)
	 301  }
	 302  
	 303  const hashRandomBytes = sys.PtrSize / 4 * 64
	 304  
	 305  // used in asm_{386,amd64,arm64}.s to seed the hash function
	 306  var aeskeysched [hashRandomBytes]byte
	 307  
	 308  // used in hash{32,64}.go to seed the hash function
	 309  var hashkey [4]uintptr
	 310  
	 311  func alginit() {
	 312  	// Install AES hash algorithms if the instructions needed are present.
	 313  	if (GOARCH == "386" || GOARCH == "amd64") &&
	 314  		cpu.X86.HasAES && // AESENC
	 315  		cpu.X86.HasSSSE3 && // PSHUFB
	 316  		cpu.X86.HasSSE41 { // PINSR{D,Q}
	 317  		initAlgAES()
	 318  		return
	 319  	}
	 320  	if GOARCH == "arm64" && cpu.ARM64.HasAES {
	 321  		initAlgAES()
	 322  		return
	 323  	}
	 324  	getRandomData((*[len(hashkey) * sys.PtrSize]byte)(unsafe.Pointer(&hashkey))[:])
	 325  	hashkey[0] |= 1 // make sure these numbers are odd
	 326  	hashkey[1] |= 1
	 327  	hashkey[2] |= 1
	 328  	hashkey[3] |= 1
	 329  }
	 330  
	 331  func initAlgAES() {
	 332  	useAeshash = true
	 333  	// Initialize with random data so hash collisions will be hard to engineer.
	 334  	getRandomData(aeskeysched[:])
	 335  }
	 336  
	 337  // Note: These routines perform the read with a native endianness.
	 338  func readUnaligned32(p unsafe.Pointer) uint32 {
	 339  	q := (*[4]byte)(p)
	 340  	if sys.BigEndian {
	 341  		return uint32(q[3]) | uint32(q[2])<<8 | uint32(q[1])<<16 | uint32(q[0])<<24
	 342  	}
	 343  	return uint32(q[0]) | uint32(q[1])<<8 | uint32(q[2])<<16 | uint32(q[3])<<24
	 344  }
	 345  
	 346  func readUnaligned64(p unsafe.Pointer) uint64 {
	 347  	q := (*[8]byte)(p)
	 348  	if sys.BigEndian {
	 349  		return uint64(q[7]) | uint64(q[6])<<8 | uint64(q[5])<<16 | uint64(q[4])<<24 |
	 350  			uint64(q[3])<<32 | uint64(q[2])<<40 | uint64(q[1])<<48 | uint64(q[0])<<56
	 351  	}
	 352  	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
	 353  }
	 354
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