github.com/dolthub/maphash@v0.1.0/runtime.go (about)

     1  // Copyright 2022 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  //
    15  // This file incorporates work covered by the following copyright and
    16  // permission notice:
    17  //
    18  // Copyright 2022 The Go Authors. All rights reserved.
    19  // Use of this source code is governed by a BSD-style
    20  // license that can be found in the LICENSE file.
    21  
    22  //go:build go1.18 || go1.19
    23  // +build go1.18 go1.19
    24  
    25  package maphash
    26  
    27  import (
    28  	"math/rand"
    29  	"unsafe"
    30  )
    31  
    32  type hashfn func(unsafe.Pointer, uintptr) uintptr
    33  
    34  func getRuntimeHasher[K comparable]() (h hashfn) {
    35  	a := any(make(map[K]struct{}))
    36  	i := (*mapiface)(unsafe.Pointer(&a))
    37  	h = i.typ.hasher
    38  	return
    39  }
    40  
    41  func newHashSeed() uintptr {
    42  	return uintptr(rand.Int())
    43  }
    44  
    45  // noescape hides a pointer from escape analysis. It is the identity function
    46  // but escape analysis doesn't think the output depends on the input.
    47  // noescape is inlined and currently compiles down to zero instructions.
    48  // USE CAREFULLY!
    49  // This was copied from the runtime (via pkg "strings"); see issues 23382 and 7921.
    50  //
    51  //go:nosplit
    52  //go:nocheckptr
    53  func noescape(p unsafe.Pointer) unsafe.Pointer {
    54  	x := uintptr(p)
    55  	return unsafe.Pointer(x ^ 0)
    56  }
    57  
    58  type mapiface struct {
    59  	typ *maptype
    60  	val *hmap
    61  }
    62  
    63  // go/src/runtime/type.go
    64  type maptype struct {
    65  	typ    _type
    66  	key    *_type
    67  	elem   *_type
    68  	bucket *_type
    69  	// function for hashing keys (ptr to key, seed) -> hash
    70  	hasher     func(unsafe.Pointer, uintptr) uintptr
    71  	keysize    uint8
    72  	elemsize   uint8
    73  	bucketsize uint16
    74  	flags      uint32
    75  }
    76  
    77  // go/src/runtime/map.go
    78  type hmap struct {
    79  	count     int
    80  	flags     uint8
    81  	B         uint8
    82  	noverflow uint16
    83  	// hash seed
    84  	hash0      uint32
    85  	buckets    unsafe.Pointer
    86  	oldbuckets unsafe.Pointer
    87  	nevacuate  uintptr
    88  	// true type is *mapextra
    89  	// but we don't need this data
    90  	extra unsafe.Pointer
    91  }
    92  
    93  // go/src/runtime/type.go
    94  type tflag uint8
    95  type nameOff int32
    96  type typeOff int32
    97  
    98  // go/src/runtime/type.go
    99  type _type struct {
   100  	size       uintptr
   101  	ptrdata    uintptr
   102  	hash       uint32
   103  	tflag      tflag
   104  	align      uint8
   105  	fieldAlign uint8
   106  	kind       uint8
   107  	equal      func(unsafe.Pointer, unsafe.Pointer) bool
   108  	gcdata     *byte
   109  	str        nameOff
   110  	ptrToThis  typeOff
   111  }