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116 lines
2.8 KiB
Go
116 lines
2.8 KiB
Go
// Copyright (C) 2015 The Protocol Authors.
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package protocol
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// The Vector type represents a version vector. The zero value is a usable
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// version vector. The vector has slice semantics and some operations on it
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// are "append-like" in that they may return the same vector modified, or v
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// new allocated Vector with the modified contents.
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type Vector []Counter
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// Counter represents a single counter in the version vector.
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type Counter struct {
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ID ShortID
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Value uint64
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}
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// Update returns a Vector with the index for the specific ID incremented by
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// one. If it is possible, the vector v is updated and returned. If it is not,
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// a copy will be created, updated and returned.
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func (v Vector) Update(id ShortID) Vector {
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for i := range v {
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if v[i].ID == id {
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// Update an existing index
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v[i].Value++
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return v
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} else if v[i].ID > id {
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// Insert a new index
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nv := make(Vector, len(v)+1)
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copy(nv, v[:i])
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nv[i].ID = id
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nv[i].Value = 1
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copy(nv[i+1:], v[i:])
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return nv
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}
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}
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// Append a new index
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return append(v, Counter{id, 1})
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}
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// Merge returns the vector containing the maximum indexes from v and b. If it
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// is possible, the vector v is updated and returned. If it is not, a copy
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// will be created, updated and returned.
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func (v Vector) Merge(b Vector) Vector {
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var vi, bi int
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for bi < len(b) {
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if vi == len(v) {
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// We've reach the end of v, all that remains are appends
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return append(v, b[bi:]...)
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}
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if v[vi].ID > b[bi].ID {
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// The index from b should be inserted here
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n := make(Vector, len(v)+1)
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copy(n, v[:vi])
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n[vi] = b[bi]
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copy(n[vi+1:], v[vi:])
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v = n
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}
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if v[vi].ID == b[bi].ID {
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if val := b[bi].Value; val > v[vi].Value {
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v[vi].Value = val
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}
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}
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if bi < len(b) && v[vi].ID == b[bi].ID {
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bi++
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}
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vi++
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}
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return v
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}
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// Copy returns an identical vector that is not shared with v.
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func (v Vector) Copy() Vector {
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nv := make(Vector, len(v))
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copy(nv, v)
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return nv
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}
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// Equal returns true when the two vectors are equivalent.
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func (v Vector) Equal(b Vector) bool {
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return v.Compare(b) == Equal
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}
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// LesserEqual returns true when the two vectors are equivalent or v is Lesser
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// than b.
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func (v Vector) LesserEqual(b Vector) bool {
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comp := v.Compare(b)
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return comp == Lesser || comp == Equal
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}
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// GreaterEqual returns true when the two vectors are equivalent or v is Greater
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// than b.
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func (v Vector) GreaterEqual(b Vector) bool {
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comp := v.Compare(b)
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return comp == Greater || comp == Equal
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}
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// Concurrent returns true when the two vectors are concurrent.
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func (v Vector) Concurrent(b Vector) bool {
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comp := v.Compare(b)
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return comp == ConcurrentGreater || comp == ConcurrentLesser
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}
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// Counter returns the current value of the given counter ID.
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func (v Vector) Counter(id ShortID) uint64 {
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for _, c := range v {
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if c.ID == id {
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return c.Value
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}
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}
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return 0
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}
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