Initial commit

vendor/github.com/cockroachdb/pebble/internal/keyspan/truncate.go

@@ -0,0 +1,60 @@
+// Copyright 2019 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package keyspan
+
+import "github.com/cockroachdb/pebble/internal/base"
+
+// Truncate creates a new iterator where every span in the supplied iterator is
+// truncated to be contained within the range [lower, upper). If start and end
+// are specified, filter out any spans that are completely outside those bounds.
+func Truncate(
+	cmp base.Compare, iter FragmentIterator, lower, upper []byte, start, end *base.InternalKey,
+) FragmentIterator {
+	return Filter(iter, func(in *Span, out *Span) (keep bool) {
+		out.Start, out.End = in.Start, in.End
+		out.Keys = append(out.Keys[:0], in.Keys...)
+
+		// Ignore this span if it lies completely outside [start, end].
+		//
+		// The comparison between s.End and start is by user key only, as
+		// the span is exclusive at s.End, so comparing by user keys
+		// is sufficient.
+		if start != nil && cmp(in.End, start.UserKey) <= 0 {
+			return false
+		}
+		if end != nil {
+			v := cmp(in.Start, end.UserKey)
+			switch {
+			case v > 0:
+				// Wholly outside the end bound. Skip it.
+				return false
+			case v == 0:
+				// This span begins at the same user key as `end`. Whether or
+				// not any of the keys contained within the span are relevant is
+				// dependent on Trailers. Any keys contained within the span
+				// with trailers larger than end cover the small sliver of
+				// keyspace between [k#inf, k#<end-seqnum>]. Since keys are
+				// sorted descending by Trailer within the span, we need to find
+				// the prefix of keys with larger trailers.
+				for i := range in.Keys {
+					if in.Keys[i].Trailer < end.Trailer {
+						out.Keys = out.Keys[:i]
+						break
+					}
+				}
+			default:
+				// Wholly within the end bound. Keep it.
+			}
+		}
+		// Truncate the bounds to lower and upper.
+		if cmp(in.Start, lower) < 0 {
+			out.Start = lower
+		}
+		if cmp(in.End, upper) > 0 {
+			out.End = upper
+		}
+		return !out.Empty() && cmp(out.Start, out.End) < 0
+	})
+}