2 files changed, 25 insertions, 47 deletions

diff --git a/lib/libc/gen/dirname.3 b/lib/libc/gen/dirname.3
index 18405f9af6ef7..60f44e2986148 100644
--- a/lib/libc/gen/dirname.3
+++ b/lib/libc/gen/dirname.3
@@ -16,7 +16,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd August 12, 2016
+.Dd September 5, 2016
 .Dt DIRNAME 3
 .Os
 .Sh NAME
@@ -60,11 +60,6 @@ space instead.
 The advantage of the former approach is that it ensures thread-safety,
 while also placing no upper limit on the supported length of the
 pathname.
-.Pp
-The algorithm used by this implementation also discards redundant
-slashes and
-.Qq \&.
-pathname components from the pathname string.
 .Sh SEE ALSO
 .Xr basename 1 ,
 .Xr dirname 1 ,
diff --git a/lib/libc/gen/dirname.c b/lib/libc/gen/dirname.c
index 621122b90c403..ae7b928d54eb8 100644
--- a/lib/libc/gen/dirname.c
+++ b/lib/libc/gen/dirname.c
@@ -27,64 +27,47 @@
 __FBSDID("$FreeBSD$");
 
 #include <libgen.h>
-#include <stdbool.h>
 #include <string.h>
 
 char *
 (dirname)(char *path)
 {
-	const char *in, *prev, *begin, *end;
-	char *out;
-	size_t prevlen;
-	bool skipslash;
+	char *end;
 
 	/*
 	 * If path is a null pointer or points to an empty string,
 	 * dirname() shall return a pointer to the string ".".
 	 */
 	if (path == NULL || *path == '\0')
-		return ((char *)".");
+		return (__DECONST(char *, "."));
 
-	/* Retain at least one leading slash character. */
-	in = out = *path == '/' ? path + 1 : path;
+	/* Find end of last pathname component. */
+	end = path + strlen(path);
+	while (end > path + 1 && *(end - 1) == '/')
+		--end;
 
-	skipslash = true;
-	prev = ".";
-	prevlen = 1;
-	for (;;) {
-		/* Extract the next pathname component. */
-		while (*in == '/')
-			++in;
-		begin = in;
-		while (*in != '/' && *in != '\0')
-			++in;
-		end = in;
-		if (begin == end)
-			break;
-
-		/*
-		 * Copy over the previous pathname component, except if
-		 * it's dot. There is no point in retaining those.
-		 */
-		if (prevlen != 1 || *prev != '.') {
-			if (!skipslash)
-				*out++ = '/';
-			skipslash = false;
-			memmove(out, prev, prevlen);
-			out += prevlen;
-		}
-
-		/* Preserve the pathname component for the next iteration. */
-		prev = begin;
-		prevlen = end - begin;
-	}
+	/* Strip off the last pathname component. */
+	while (end > path && *(end - 1) != '/')
+		--end;
 
 	/*
 	 * If path does not contain a '/', then dirname() shall return a
 	 * pointer to the string ".".
 	 */
-	if (out == path)
-		*out++ = '.';
-	*out = '\0';
+	if (end == path) {
+		path[0] = '.';
+		path[1] = '\0';
+		return (path);
+	}
+
+	/*
+	 * Remove trailing slashes from the resulting directory name. Ensure
+	 * that at least one character remains.
+	 */
+	while (end > path + 1 && *(end - 1) == '/')
+		--end;
+
+	/* Null terminate directory name and return it. */
+	*end = '\0';
 	return (path);
 }