--- /dev/null
+// Copyright 2013 The Go 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 godoc
+
+// ----------------------------------------------------------------------------
+// SpotInfo
+
+// A SpotInfo value describes a particular identifier spot in a given file;
+// It encodes three values: the SpotKind (declaration or use), a line or
+// snippet index "lori", and whether it's a line or index.
+//
+// The following encoding is used:
+//
+// bits 32 4 1 0
+// value [lori|kind|isIndex]
+//
+type SpotInfo uint32
+
+// SpotKind describes whether an identifier is declared (and what kind of
+// declaration) or used.
+type SpotKind uint32
+
+const (
+ PackageClause SpotKind = iota
+ ImportDecl
+ ConstDecl
+ TypeDecl
+ VarDecl
+ FuncDecl
+ MethodDecl
+ Use
+ nKinds
+)
+
+var (
+ // These must match the SpotKind values above.
+ name = []string{
+ "Packages",
+ "Imports",
+ "Constants",
+ "Types",
+ "Variables",
+ "Functions",
+ "Methods",
+ "Uses",
+ "Unknown",
+ }
+)
+
+func (x SpotKind) Name() string { return name[x] }
+
+func init() {
+ // sanity check: if nKinds is too large, the SpotInfo
+ // accessor functions may need to be updated
+ if nKinds > 8 {
+ panic("internal error: nKinds > 8")
+ }
+}
+
+// makeSpotInfo makes a SpotInfo.
+func makeSpotInfo(kind SpotKind, lori int, isIndex bool) SpotInfo {
+ // encode lori: bits [4..32)
+ x := SpotInfo(lori) << 4
+ if int(x>>4) != lori {
+ // lori value doesn't fit - since snippet indices are
+ // most certainly always smaller then 1<<28, this can
+ // only happen for line numbers; give it no line number (= 0)
+ x = 0
+ }
+ // encode kind: bits [1..4)
+ x |= SpotInfo(kind) << 1
+ // encode isIndex: bit 0
+ if isIndex {
+ x |= 1
+ }
+ return x
+}
+
+func (x SpotInfo) Kind() SpotKind { return SpotKind(x >> 1 & 7) }
+func (x SpotInfo) Lori() int { return int(x >> 4) }
+func (x SpotInfo) IsIndex() bool { return x&1 != 0 }