github.com/zuoyebang/bitalosdb@v1.1.1-0.20240516111551-79a8c4d8ce20/internal/bindex/bits.go (about)

     1  // Copyright 2021 The Bitalosdb author(hustxrb@163.com) and other contributors.
     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  //go:build !amd64 || nosimd
    16  
    17  package bindex
    18  
    19  import (
    20  	"math/bits"
    21  	"unsafe"
    22  )
    23  
    24  const (
    25  	groupSize       = 8
    26  	maxAvgGroupLoad = 7
    27  
    28  	loBits uint64 = 0x0101010101010101
    29  	hiBits uint64 = 0x8080808080808080
    30  )
    31  
    32  type bitset uint64
    33  
    34  func metaMatchH2(m *metadata, h h2) bitset {
    35  	return hasZeroByte(castUint64(m) ^ (loBits * uint64(h)))
    36  }
    37  
    38  func metaMatchEmpty(m *metadata) bitset {
    39  	return hasZeroByte(castUint64(m) ^ hiBits)
    40  }
    41  
    42  func nextMatch(b *bitset) uint32 {
    43  	s := uint32(bits.TrailingZeros64(uint64(*b)))
    44  	*b &= ^(1 << s) // clear bit |s|
    45  	return s >> 3   // div by 8
    46  }
    47  
    48  func hasZeroByte(x uint64) bitset {
    49  	return bitset(((x - loBits) & ^(x)) & hiBits)
    50  }
    51  
    52  func castUint64(m *metadata) uint64 {
    53  	return *(*uint64)((unsafe.Pointer)(m))
    54  }