Roy Crihfield
6bb6d4e27f
* pull changes from geth fork * update deps * remove unused: StartPath, SubtrieIteratorFactory * change module name
143 lines
4.2 KiB
Go
143 lines
4.2 KiB
Go
//
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// Copyright © 2020 Vulcanize, Inc
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Affero General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Affero General Public License for more details.
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//
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// You should have received a copy of the GNU Affero General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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package iterator
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import (
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"bytes"
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"math/bits"
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"github.com/ethereum/go-ethereum/trie"
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)
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// PrefixBoundIterator is a NodeIterator constrained by a lower & upper bound (as hex path prefixes)
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type PrefixBoundIterator struct {
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trie.NodeIterator
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EndPath []byte
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}
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// IteratorConstructor is a constructor returning a NodeIterator, which is used to decouple this
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// code from the trie implementation.
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type IteratorConstructor = func(startKey []byte) trie.NodeIterator
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func (it *PrefixBoundIterator) Next(descend bool) bool {
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if it.EndPath == nil {
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return it.NodeIterator.Next(descend)
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}
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if !it.NodeIterator.Next(descend) {
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return false
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}
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// stop if underlying iterator went past upper bound
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cmp := bytes.Compare(it.Path(), it.EndPath)
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return cmp <= 0
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}
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// NewPrefixBoundIterator returns an iterator with an upper bound value (hex path prefix)
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func NewPrefixBoundIterator(it trie.NodeIterator, to []byte) *PrefixBoundIterator {
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return &PrefixBoundIterator{NodeIterator: it, EndPath: to}
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}
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// generates nibble slice prefixes at uniform intervals
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type prefixGenerator struct {
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current []byte
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step byte
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stepIndex uint
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}
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func newPrefixGenerator(nbins uint) prefixGenerator {
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if bits.OnesCount(nbins) != 1 {
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panic("nbins must be a power of 2")
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}
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// determine step dist. and path index at which to step
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var step byte
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var stepIndex uint
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for ; nbins != 0; stepIndex++ {
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divisor := byte(nbins & 0xF)
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if divisor != 0 {
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step = 0x10 / divisor
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}
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nbins = nbins >> 4
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}
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return prefixGenerator{
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current: make([]byte, stepIndex),
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step: step,
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stepIndex: stepIndex - 1,
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}
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}
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func (gen *prefixGenerator) Value() []byte {
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return gen.current
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}
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func (gen *prefixGenerator) HasNext() bool {
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return gen.current[0] < 0x10
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}
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func (gen *prefixGenerator) Next() {
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// increment the cursor, and handle overflow
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gen.current[gen.stepIndex] += gen.step
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overflow := false
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for ix := 0; ix < len(gen.current); ix++ {
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rix := len(gen.current) - 1 - ix // index in prefix is reverse
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if overflow { // apply overflow
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gen.current[rix]++
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overflow = false
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}
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// detect overflow at this index
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if rix != 0 && gen.current[rix] > 0xf {
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gen.current[rix] = 0
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overflow = true
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}
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}
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}
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// MakePaths generates paths that cut trie domain into `nbins` uniform conterminous bins (w/ opt. prefix)
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// eg. MakePaths([], 2) => [[0] [8]]
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// MakePaths([4], 32) => [[4 0 0] [4 0 8] [4 1 0]... [4 f 8]]
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func MakePaths(prefix []byte, nbins uint) [][]byte {
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var res [][]byte
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for it := newPrefixGenerator(nbins); it.HasNext(); it.Next() {
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next := make([]byte, len(prefix))
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copy(next, prefix)
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next = append(next, it.Value()...)
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res = append(res, next)
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}
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return res
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}
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func eachPrefixRange(prefix []byte, nbins uint, callback func([]byte, []byte)) {
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prefixes := MakePaths(prefix, nbins)
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prefixes = append(prefixes, nil) // include tail
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prefixes[0] = nil // set bin 0 left bound to nil to include root
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for i := 0; i < len(prefixes)-1; i++ {
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key := prefixes[i]
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if len(key)%2 != 0 { // zero-pad for odd-length keys
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key = append(key, 0)
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}
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callback(key, prefixes[i+1])
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}
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}
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// SubtrieIterators cuts a trie by path prefix, returning `nbins` iterators covering its subtries
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func SubtrieIterators(makeIterator IteratorConstructor, nbins uint) []trie.NodeIterator {
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var iters []trie.NodeIterator
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eachPrefixRange(nil, nbins, func(from []byte, to []byte) {
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it := makeIterator(HexToKeyBytes(from))
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iters = append(iters, NewPrefixBoundIterator(it, to))
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})
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return iters
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}
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