syncthing/lib/protocol/vector.go
2015-09-22 21:51:05 +02:00

116 lines
2.8 KiB
Go

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