Add 'mru/' from commit '2899885c4220560df4f60e4c052a6ab9773a0386'

git-subtree-dir: mru
git-subtree-mainline: cf2b016433
git-subtree-split: 2899885c42

mru/timestamps.go

@@ -0,0 +1,101 @@
+package mru
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"sort"
+)
+
+// timestamps contains datastructures for maintaining a list of keys sortable
+// by timestamp.
+
+type timestamp struct {
+	t int64
+	k string
+}
+
+type timestamps struct {
+	ts  []timestamp
+	cap int
+}
+
+func newTimestamps(icap int) *timestamps {
+	return &timestamps{
+		ts:  make([]timestamp, 0, icap),
+		cap: icap,
+	}
+}
+
+func (ts *timestamps) K(i int) string {
+	return ts.ts[i].k
+}
+
+func (ts *timestamps) T(i int) int64 {
+	return ts.ts[i].t
+}
+
+func (ts *timestamps) Len() int {
+	return len(ts.ts)
+}
+
+func (ts *timestamps) Less(i, j int) bool {
+	return ts.ts[i].t < ts.ts[j].t
+}
+
+func (ts *timestamps) Swap(i, j int) {
+	ts.ts[i], ts.ts[j] = ts.ts[j], ts.ts[i]
+}
+
+func (ts *timestamps) Find(k string) (int, bool) {
+	for i := range len(ts.ts) {
+		if ts.ts[i].k == k {
+			return i, true
+		}
+	}
+	return -1, false
+}
+
+func (ts *timestamps) Update(k string, t int64) bool {
+	i, ok := ts.Find(k)
+	if !ok {
+		ts.ts = append(ts.ts, timestamp{t, k})
+		sort.Sort(ts)
+		return false
+	}
+
+	ts.ts[i].t = t
+	sort.Sort(ts)
+	return true
+}
+
+func (ts *timestamps) ConsistencyCheck() error {
+	if !sort.IsSorted(ts) {
+		return errors.New("mru: timestamps are not sorted")
+	}
+
+	keys := map[string]bool{}
+	for i := range ts.ts {
+		if keys[ts.ts[i].k] {
+			return fmt.Errorf("duplicate key %s detected", ts.ts[i].k)
+		}
+		keys[ts.ts[i].k] = true
+	}
+
+	if len(keys) != len(ts.ts) {
+		return fmt.Errorf("mru: timestamp contains %d duplicate keys",
+			len(ts.ts)-len(keys))
+	}
+
+	return nil
+}
+
+func (ts *timestamps) Delete(i int) {
+	ts.ts = append(ts.ts[:i], ts.ts[i+1:]...)
+}
+
+func (ts *timestamps) Dump(w io.Writer) {
+	for i := range ts.ts {
+		fmt.Fprintf(w, "%d: %s, %d\n", i, ts.K(i), ts.T(i))
+	}
+}