[PATCH 2/9] Add functions get_relative_cwd() and is_inside_dir()

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

The function get_relative_cwd() works just as getcwd(), only that it
takes an absolute path as additional parameter, returning the prefix
of the current working directory relative to the given path.  If the
cwd is no subdirectory of the given path, it returns NULL.

is_inside_dir() is just a trivial wrapper over get_relative_cwd().

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 dir.c |   30 ++++++++++++++++++++++++++++++
 dir.h |    3 +++
 2 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/dir.c b/dir.c
index 8d8faf5..ef67d6f 100644
--- a/dir.c
+++ b/dir.c
@@ -642,3 +642,33 @@ file_exists(const char *f)
   struct stat sb;
   return stat(f, &sb) == 0;
 }
+
+char *get_relative_cwd(char *buffer, int size, const char *dir)
+{
+	char *cwd = buffer;
+
+	if (!dir)
+		return 0;
+
+	if (!getcwd(buffer, size))
+		return 0;
+
+	if (!is_absolute_path(dir))
+		dir = make_absolute_path(dir);
+
+	while (*dir && *dir == *cwd) {
+		dir++;
+		cwd++;
+	}
+	if (*dir)
+		return NULL;
+	if (*cwd == '/')
+		return cwd + 1;
+	return cwd;
+}
+
+int is_inside_dir(const char *dir)
+{
+	char buffer[PATH_MAX];
+	return get_relative_cwd(buffer, sizeof(buffer), dir) != NULL;
+}
diff --git a/dir.h b/dir.h
index ec0e8ab..f55a87b 100644
--- a/dir.h
+++ b/dir.h
@@ -61,4 +61,7 @@ extern void add_exclude(const char *string, const char *base,
 extern int file_exists(const char *);
 extern struct dir_entry *dir_add_name(struct dir_struct *dir, const char *pathname, int len);
 
+extern char *get_relative_cwd(char *buffer, int size, const char *dir);
+extern int is_inside_dir(const char *dir);
+
 #endif
-- 
1.5.3.rc3.28.g1406