github.com/bytedance/gopkg@v0.0.0-20240514070511-01b2cbcf35e1/collection/skipmap/util.go (about)

     1  // Copyright 2021 ByteDance 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  package skipmap
    16  
    17  import (
    18  	_ "unsafe" // for linkname
    19  
    20  	"github.com/bytedance/gopkg/internal/wyhash"
    21  	"github.com/bytedance/gopkg/lang/fastrand"
    22  )
    23  
    24  const (
    25  	maxLevel            = 16
    26  	p                   = 0.25
    27  	defaultHighestLevel = 3
    28  )
    29  
    30  func hash(s string) uint64 {
    31  	return wyhash.Sum64String(s)
    32  }
    33  
    34  //go:linkname cmpstring runtime.cmpstring
    35  func cmpstring(a, b string) int
    36  
    37  func randomLevel() int {
    38  	level := 1
    39  	for fastrand.Uint32n(1/p) == 0 {
    40  		level++
    41  	}
    42  	if level > maxLevel {
    43  		return maxLevel
    44  	}
    45  	return level
    46  }