github.com/SmartMeshFoundation/Spectrum@v0.0.0-20220621030607-452a266fee1e/core/bloombits/generator.go (about)

     1  // Copyright 2017 The Spectrum Authors
     2  // This file is part of the Spectrum library.
     3  //
     4  // The Spectrum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The Spectrum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the Spectrum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package bloombits
    18  
    19  import (
    20  	"errors"
    21  
    22  	"github.com/SmartMeshFoundation/Spectrum/core/types"
    23  )
    24  
    25  // errSectionOutOfBounds is returned if the user tried to add more bloom filters
    26  // to the batch than available space, or if tries to retrieve above the capacity,
    27  var errSectionOutOfBounds = errors.New("section out of bounds")
    28  
    29  // Generator takes a number of bloom filters and generates the rotated bloom bits
    30  // to be used for batched filtering.
    31  type Generator struct {
    32  	blooms   [types.BloomBitLength][]byte // Rotated blooms for per-bit matching
    33  	sections uint                         // Number of sections to batch together
    34  	nextBit  uint                         // Next bit to set when adding a bloom
    35  }
    36  
    37  // NewGenerator creates a rotated bloom generator that can iteratively fill a
    38  // batched bloom filter's bits.
    39  func NewGenerator(sections uint) (*Generator, error) {
    40  	if sections%8 != 0 {
    41  		return nil, errors.New("section count not multiple of 8")
    42  	}
    43  	b := &Generator{sections: sections}
    44  	for i := 0; i < types.BloomBitLength; i++ {
    45  		b.blooms[i] = make([]byte, sections/8)
    46  	}
    47  	return b, nil
    48  }
    49  
    50  // AddBloom takes a single bloom filter and sets the corresponding bit column
    51  // in memory accordingly.
    52  func (b *Generator) AddBloom(index uint, bloom types.Bloom) error {
    53  	// Make sure we're not adding more bloom filters than our capacity
    54  	if b.nextBit >= b.sections {
    55  		return errSectionOutOfBounds
    56  	}
    57  	if b.nextBit != index {
    58  		return errors.New("bloom filter with unexpected index")
    59  	}
    60  	// Rotate the bloom and insert into our collection
    61  	byteIndex := b.nextBit / 8
    62  	bitMask := byte(1) << byte(7-b.nextBit%8)
    63  
    64  	for i := 0; i < types.BloomBitLength; i++ {
    65  		bloomByteIndex := types.BloomByteLength - 1 - i/8
    66  		bloomBitMask := byte(1) << byte(i%8)
    67  
    68  		if (bloom[bloomByteIndex] & bloomBitMask) != 0 {
    69  			b.blooms[i][byteIndex] |= bitMask
    70  		}
    71  	}
    72  	b.nextBit++
    73  
    74  	return nil
    75  }
    76  
    77  // Bitset returns the bit vector belonging to the given bit index after all
    78  // blooms have been added.
    79  func (b *Generator) Bitset(idx uint) ([]byte, error) {
    80  	if b.nextBit != b.sections {
    81  		return nil, errors.New("bloom not fully generated yet")
    82  	}
    83  	if idx >= b.sections {
    84  		return nil, errSectionOutOfBounds
    85  	}
    86  	return b.blooms[idx], nil
    87  }