maphash: copy source from v0.1.0

contrab/maphash/README.md

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+# maphash
+
+kanged from github.com/dolthub/[email protected]

contrab/maphash/hasher.go

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+// Copyright 2022 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package maphash
+
+import "unsafe"
+
+// Hasher hashes values of type K.
+// Uses runtime AES-based hashing.
+type Hasher[K comparable] struct {
+	hash hashfn
+	seed uintptr
+}
+
+// NewHasher creates a new Hasher[K] with a random seed.
+func NewHasher[K comparable]() Hasher[K] {
+	return Hasher[K]{
+		hash: getRuntimeHasher[K](),
+		seed: newHashSeed(),
+	}
+}
+
+// NewSeed returns a copy of |h| with a new hash seed.
+func NewSeed[K comparable](h Hasher[K]) Hasher[K] {
+	return Hasher[K]{
+		hash: h.hash,
+		seed: newHashSeed(),
+	}
+}
+
+// Hash hashes |key|.
+func (h Hasher[K]) Hash(key K) uint64 {
+	// promise to the compiler that pointer
+	// |p| does not escape the stack.
+	p := noescape(unsafe.Pointer(&key))
+	return uint64(h.hash(p, h.seed))
+}

contrab/maphash/runtime.go

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+// Copyright 2022 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file incorporates work covered by the following copyright and
+// permission notice:
+//
+// Copyright 2022 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.
+
+//go:build go1.18 || go1.19
+// +build go1.18 go1.19
+
+package maphash
+
+import (
+	"math/rand"
+	"unsafe"
+)
+
+type hashfn func(unsafe.Pointer, uintptr) uintptr
+
+func getRuntimeHasher[K comparable]() (h hashfn) {
+	a := any(make(map[K]struct{}))
+	i := (*mapiface)(unsafe.Pointer(&a))
+	h = i.typ.hasher
+	return
+}
+
+func newHashSeed() uintptr {
+	return uintptr(rand.Int())
+}
+
+// noescape hides a pointer from escape analysis. It is the identity function
+// but escape analysis doesn't think the output depends on the input.
+// noescape is inlined and currently compiles down to zero instructions.
+// USE CAREFULLY!
+// This was copied from the runtime (via pkg "strings"); see issues 23382 and 7921.
+//
+//go:nosplit
+//go:nocheckptr
+func noescape(p unsafe.Pointer) unsafe.Pointer {
+	x := uintptr(p)
+	return unsafe.Pointer(x ^ 0)
+}
+
+type mapiface struct {
+	typ *maptype
+	val *hmap
+}
+
+// go/src/runtime/type.go
+type maptype struct {
+	typ    _type
+	key    *_type
+	elem   *_type
+	bucket *_type
+	// function for hashing keys (ptr to key, seed) -> hash
+	hasher     func(unsafe.Pointer, uintptr) uintptr
+	keysize    uint8
+	elemsize   uint8
+	bucketsize uint16
+	flags      uint32
+}
+
+// go/src/runtime/map.go
+type hmap struct {
+	count     int
+	flags     uint8
+	B         uint8
+	noverflow uint16
+	// hash seed
+	hash0      uint32
+	buckets    unsafe.Pointer
+	oldbuckets unsafe.Pointer
+	nevacuate  uintptr
+	// true type is *mapextra
+	// but we don't need this data
+	extra unsafe.Pointer
+}
+
+// go/src/runtime/type.go
+type tflag uint8
+type nameOff int32
+type typeOff int32
+
+// go/src/runtime/type.go
+type _type struct {
+	size       uintptr
+	ptrdata    uintptr
+	hash       uint32
+	tflag      tflag
+	align      uint8
+	fieldAlign uint8
+	kind       uint8
+	equal      func(unsafe.Pointer, unsafe.Pointer) bool
+	gcdata     *byte
+	str        nameOff
+	ptrToThis  typeOff
+}