src/runtime/alg.go

// 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 (
	"internal/abi"
	"internal/byteorder"
	"internal/goarch"
	"internal/runtime/maps"
	"internal/runtime/sys"
	"unsafe"
)

const (
	// We use 32-bit hash on Wasm, see hash32.go.
	hashSize = (1-goarch.IsWasm)*goarch.PtrSize + goarch.IsWasm*4
	c0       = uintptr((8-hashSize)/4*2860486313 + (hashSize-4)/4*33054211828000289)
	c1       = uintptr((8-hashSize)/4*3267000013 + (hashSize-4)/4*23344194077549503)
)

func trimHash(h uintptr) uintptr {
	if goarch.IsWasm != 0 {
		// On Wasm, we use 32-bit hash, despite that uintptr is 64-bit.
		// memhash* always returns a uintptr with high 32-bit being 0
		// (see hash32.go). We trim the hash in other places where we
		// compute the hash manually, e.g. in interhash.
		return uintptr(uint32(h))
	}
	return h
}

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 memhash128(p unsafe.Pointer, h uintptr) uintptr {
	return memhash(p, h, 16)
}

//go:nosplit
func memhash_varlen(p unsafe.Pointer, h uintptr) uintptr {
	ptr := sys.GetClosurePtr()
	size := *(*uintptr)(unsafe.Pointer(ptr + unsafe.Sizeof(h)))
	return memhash(p, h, size)
}

// This is simple wrappers.
// It's better to use maps.MemHash functions directly,
// but we have reflection code that still calls hashing from runtime via LookupRuntime,
// so we have to try to minimize overhead of an extra call.
// For this add nosplit for performance

// memhash should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/aacfactory/fns
//   - github.com/dgraph-io/ristretto
//   - github.com/minio/simdjson-go
//   - github.com/nbd-wtf/go-nostr
//   - github.com/outcaste-io/ristretto
//   - github.com/puzpuzpuz/xsync/v2
//   - github.com/puzpuzpuz/xsync/v3
//   - github.com/authzed/spicedb
//   - github.com/pingcap/badger
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:nosplit
//go:linkname memhash
func memhash(p unsafe.Pointer, h, s uintptr) uintptr {
	return maps.MemHash(p, h, s)
}

//go:nosplit
func memhash64(p unsafe.Pointer, seed uintptr) uintptr {
	return maps.MemHash64(readUnaligned64(p), seed)
}

//go:nosplit
func memhash32(p unsafe.Pointer, seed uintptr) uintptr {
	return maps.MemHash32(readUnaligned32(p), seed)
}

// strhash should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/aristanetworks/goarista
//   - github.com/bytedance/sonic
//   - github.com/bytedance/go-tagexpr/v2
//   - github.com/cloudwego/dynamicgo
//   - github.com/v2fly/v2ray-core/v5
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:nosplit
//go:linkname strhash
func strhash(p unsafe.Pointer, h uintptr) uintptr {
	return maps.StrHash(*(*string)(p), h)
}

// 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 trimHash(c1 * (c0 ^ h)) // +0, -0
	case f != f:
		return trimHash(c1 * (c0 ^ h ^ uintptr(rand()))) // 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 trimHash(c1 * (c0 ^ h)) // +0, -0
	case f != f:
		return trimHash(c1 * (c0 ^ h ^ uintptr(rand()))) // 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
	if t.Equal == nil {
		// Check hashability here. We could do this check inside
		// typehash, but we want to report the topmost type in
		// the error text (e.g. in a struct with a field of slice type
		// we want to report the struct, not the slice).
		panic(errorString("hash of unhashable type " + toRType(t).string()))
	}
	if t.IsDirectIface() {
		return trimHash(c1 * typehash(t, unsafe.Pointer(&a.data), h^c0))
	} else {
		return trimHash(c1 * typehash(t, a.data, h^c0))
	}
}

// nilinterhash should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/anacrolix/stm
//   - github.com/aristanetworks/goarista
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname nilinterhash
func nilinterhash(p unsafe.Pointer, h uintptr) uintptr {
	a := (*eface)(p)
	t := a._type
	if t == nil {
		return h
	}
	if t.Equal == nil {
		// See comment in interhash above.
		panic(errorString("hash of unhashable type " + toRType(t).string()))
	}
	if t.IsDirectIface() {
		return trimHash(c1 * typehash(t, unsafe.Pointer(&a.data), h^c0))
	} else {
		return trimHash(c1 * typehash(t, a.data, h^c0))
	}
}

// typehash computes the hash of the object of type t at address p.
// h is the seed.
// This function is seldom used. Most maps use for hashing either
// fixed functions (e.g. f32hash) or compiler-generated functions
// (e.g. for a type like struct { x, y string }). This implementation
// is slower but more general and is used for hashing interface types
// (called from interhash or nilinterhash, above) or for hashing in
// maps generated by reflect.MapOf (reflect_typehash, below).
//
// typehash should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/puzpuzpuz/xsync/v2
//   - github.com/puzpuzpuz/xsync/v3
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname typehash
func typehash(t *_type, p unsafe.Pointer, h uintptr) uintptr {
	if t.TFlag&abi.TFlagRegularMemory != 0 {
		// Handle ptr sizes specially, see issue 37086.
		switch t.Size_ {
		case 4:
			return memhash32(p, h)
		case 8:
			return memhash64(p, h)
		default:
			return memhash(p, h, t.Size_)
		}
	}
	switch t.Kind() {
	case abi.Float32:
		return f32hash(p, h)
	case abi.Float64:
		return f64hash(p, h)
	case abi.Complex64:
		return c64hash(p, h)
	case abi.Complex128:
		return c128hash(p, h)
	case abi.String:
		return strhash(p, h)
	case abi.Interface:
		i := (*interfacetype)(unsafe.Pointer(t))
		if len(i.Methods) == 0 {
			return nilinterhash(p, h)
		}
		return interhash(p, h)
	case abi.Array:
		a := (*arraytype)(unsafe.Pointer(t))
		for i := uintptr(0); i < a.Len; i++ {
			h = typehash(a.Elem, add(p, i*a.Elem.Size_), h)
		}
		return h
	case abi.Struct:
		s := (*structtype)(unsafe.Pointer(t))
		for _, f := range s.Fields {
			if f.Name.IsBlank() {
				continue
			}
			h = typehash(f.Typ, add(p, f.Offset), h)
		}
		return h
	default:
		// Should never happen, as typehash should only be called
		// with comparable types.
		panic(errorString("hash of unhashable type " + toRType(t).string()))
	}
}

//go:linkname reflect_typehash reflect.typehash
func reflect_typehash(t *_type, p unsafe.Pointer, h uintptr) uintptr {
	return typehash(t, p, h)
}

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 {
	x := *(*iface)(p)
	y := *(*iface)(q)
	return x.tab == y.tab && ifaceeq(x.tab, x.data, y.data)
}
func nilinterequal(p, q unsafe.Pointer) bool {
	x := *(*eface)(p)
	y := *(*eface)(q)
	return x._type == y._type && efaceeq(x._type, x.data, y.data)
}
func efaceeq(t *_type, x, y unsafe.Pointer) bool {
	if t == nil {
		return true
	}
	eq := t.Equal
	if eq == nil {
		panic(errorString("comparing uncomparable type " + toRType(t).string()))
	}
	if t.IsDirectIface() {
		// Direct interface types are ptr, chan, map, func, and single-element structs/arrays thereof.
		// Maps and funcs are not comparable, so they can't reach here.
		// Ptrs, chans, and single-element items can be compared directly using ==.
		return x == y
	}
	return eq(x, y)
}
func ifaceeq(tab *itab, x, y unsafe.Pointer) bool {
	if tab == nil {
		return true
	}
	t := tab.Type
	eq := t.Equal
	if eq == nil {
		panic(errorString("comparing uncomparable type " + toRType(t).string()))
	}
	if t.IsDirectIface() {
		// See comment in efaceeq.
		return x == y
	}
	return eq(x, y)
}

// Testing adapters for hash quality tests (see hash_test.go)
//
// stringHash should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/k14s/starlark-go
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname stringHash
func stringHash(s string, seed uintptr) uintptr {
	return strhash(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 memhash32(noescape(unsafe.Pointer(&i)), seed)
}

func int64Hash(i uint64, seed uintptr) uintptr {
	return memhash64(noescape(unsafe.Pointer(&i)), seed)
}

func efaceHash(i any, seed uintptr) uintptr {
	return nilinterhash(noescape(unsafe.Pointer(&i)), seed)
}

func ifaceHash(i interface {
	F()
}, seed uintptr) uintptr {
	return interhash(noescape(unsafe.Pointer(&i)), seed)
}

func readUnaligned32(p unsafe.Pointer) uint32 {
	q := (*[4]byte)(p)
	if goarch.BigEndian {
		return byteorder.BEUint32(q[:])
	}
	return byteorder.LEUint32(q[:])
}

func readUnaligned64(p unsafe.Pointer) uint64 {
	q := (*[8]byte)(p)
	if goarch.BigEndian {
		return byteorder.BEUint64(q[:])
	}
	return byteorder.LEUint64(q[:])
}