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maphash: copy source from v0.1.0
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3
contrab/maphash/README.md
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contrab/maphash/README.md
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# maphash
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kanged from github.com/dolthub/maphash@v0.1.0
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48
contrab/maphash/hasher.go
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48
contrab/maphash/hasher.go
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// Copyright 2022 Dolthub, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package maphash
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import "unsafe"
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// Hasher hashes values of type K.
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// Uses runtime AES-based hashing.
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type Hasher[K comparable] struct {
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hash hashfn
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seed uintptr
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}
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// NewHasher creates a new Hasher[K] with a random seed.
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func NewHasher[K comparable]() Hasher[K] {
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return Hasher[K]{
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hash: getRuntimeHasher[K](),
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seed: newHashSeed(),
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}
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}
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// NewSeed returns a copy of |h| with a new hash seed.
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func NewSeed[K comparable](h Hasher[K]) Hasher[K] {
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return Hasher[K]{
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hash: h.hash,
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seed: newHashSeed(),
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}
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}
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// Hash hashes |key|.
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func (h Hasher[K]) Hash(key K) uint64 {
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// promise to the compiler that pointer
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// |p| does not escape the stack.
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p := noescape(unsafe.Pointer(&key))
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return uint64(h.hash(p, h.seed))
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}
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111
contrab/maphash/runtime.go
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111
contrab/maphash/runtime.go
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// Copyright 2022 Dolthub, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// This file incorporates work covered by the following copyright and
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// permission notice:
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//
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// Copyright 2022 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build go1.18 || go1.19
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// +build go1.18 go1.19
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package maphash
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import (
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"math/rand"
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"unsafe"
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)
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type hashfn func(unsafe.Pointer, uintptr) uintptr
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func getRuntimeHasher[K comparable]() (h hashfn) {
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a := any(make(map[K]struct{}))
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i := (*mapiface)(unsafe.Pointer(&a))
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h = i.typ.hasher
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return
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}
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func newHashSeed() uintptr {
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return uintptr(rand.Int())
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}
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// noescape hides a pointer from escape analysis. It is the identity function
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// but escape analysis doesn't think the output depends on the input.
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// noescape is inlined and currently compiles down to zero instructions.
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// USE CAREFULLY!
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// This was copied from the runtime (via pkg "strings"); see issues 23382 and 7921.
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//
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//go:nosplit
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//go:nocheckptr
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func noescape(p unsafe.Pointer) unsafe.Pointer {
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x := uintptr(p)
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return unsafe.Pointer(x ^ 0)
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}
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type mapiface struct {
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typ *maptype
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val *hmap
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}
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// go/src/runtime/type.go
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type maptype struct {
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typ _type
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key *_type
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elem *_type
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bucket *_type
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// function for hashing keys (ptr to key, seed) -> hash
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hasher func(unsafe.Pointer, uintptr) uintptr
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keysize uint8
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elemsize uint8
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bucketsize uint16
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flags uint32
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}
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// go/src/runtime/map.go
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type hmap struct {
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count int
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flags uint8
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B uint8
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noverflow uint16
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// hash seed
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hash0 uint32
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buckets unsafe.Pointer
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oldbuckets unsafe.Pointer
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nevacuate uintptr
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// true type is *mapextra
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// but we don't need this data
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extra unsafe.Pointer
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}
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// go/src/runtime/type.go
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type tflag uint8
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type nameOff int32
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type typeOff int32
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// go/src/runtime/type.go
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type _type struct {
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size uintptr
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ptrdata uintptr
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hash uint32
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tflag tflag
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align uint8
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fieldAlign uint8
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kind uint8
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equal func(unsafe.Pointer, unsafe.Pointer) bool
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gcdata *byte
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str nameOff
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ptrToThis typeOff
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}
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