1 files changed, 52 insertions, 0 deletions
diff --git a/src/pkg/go/doc/synopsis.go b/src/pkg/go/doc/synopsis.go
new file mode 100644
index 000000000..2192d78c0
--- /dev/null
+++ b/src/pkg/go/doc/synopsis.go
@@ -0,0 +1,52 @@
+// Copyright 2012 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 doc
+
+import "unicode"
+
+// firstSentenceLen returns the length of the first sentence in s.
+// The sentence ends after the first period followed by space and
+// not preceded by exactly one uppercase letter.
+//
+func firstSentenceLen(s string) int {
+	var ppp, pp, p rune
+	for i, q := range s {
+		if q == '\n' || q == '\r' || q == '\t' {
+			q = ' '
+		}
+		if q == ' ' && p == '.' && (!unicode.IsUpper(pp) || unicode.IsUpper(ppp)) {
+			return i
+		}
+		ppp, pp, p = pp, p, q
+	}
+	return len(s)
+}
+
+// Synopsis returns a cleaned version of the first sentence in s.
+// That sentence ends after the first period followed by space and
+// not preceded by exactly one uppercase letter. The result string
+// has no \n, \r, or \t characters and uses only single spaces between
+// words.
+//
+func Synopsis(s string) string {
+	n := firstSentenceLen(s)
+	var b []byte
+	p := byte(' ')
+	for i := 0; i < n; i++ {
+		q := s[i]
+		if q == '\n' || q == '\r' || q == '\t' {
+			q = ' '
+		}
+		if q != ' ' || p != ' ' {
+			b = append(b, q)
+			p = q
+		}
+	}
+	// remove trailing blank, if any
+	if n := len(b); n > 0 && p == ' ' {
+		b = b[0 : n-1]
+	}
+	return string(b)
+}