Index: trunk/scconfig/Rev.h
===================================================================
--- trunk/scconfig/Rev.h	(revision 6720)
+++ trunk/scconfig/Rev.h	(revision 6721)
@@ -1 +1 @@
-static const int myrev = 6681;
+static const int myrev = 6720;
Index: trunk/scconfig/Rev.tab
===================================================================
--- trunk/scconfig/Rev.tab	(revision 6720)
+++ trunk/scconfig/Rev.tab	(revision 6721)
@@ -1,4 +1,4 @@
-6681	configure	new libcschem source file for project support
+6720	configure	new libcschem source file for project support
 6294	configure	remove excess export API
 6180	configure	move plug_io_act from lib to sch-rnd as it depends on sch-rnd assumptions on project file naming and file formats and other implementation-specific details
 6070	configure	rnd_printf support for %rc for printing 'k' coords properly
Index: trunk/src/libcschem/Makefile.in
===================================================================
--- trunk/src/libcschem/Makefile.in	(revision 6720)
+++ trunk/src/libcschem/Makefile.in	(revision 6721)
@@ -49,6 +49,7 @@
  util_grp.o
  util_lib_fs.o
  util_loclib.o
+ util_path.o
  util_parse.o
  util_project.o
  util_wirenet.o
Index: trunk/src/libcschem/util_path.c
===================================================================
--- trunk/src/libcschem/util_path.c	(nonexistent)
+++ trunk/src/libcschem/util_path.c	(revision 6721)
@@ -0,0 +1,72 @@
+/*
+ *                            COPYRIGHT
+ *
+ *  cschem - modular/flexible schematics editor - libcschem (core library)
+ *  Copyright (C) 2023 Tibor 'Igor2' Palinkas
+ *
+ *  (Supported by NLnet NGI0 Entrust in 2023)
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.*
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ *  Contact:
+ *    Project page: http://repo.hu/projects/sch-rnd
+ *    contact lead developer: http://www.repo.hu/projects/sch-rnd/contact.html
+ *    mailing list: http://www.repo.hu/projects/sch-rnd/contact.html
+ */
+
+#include "config.h"
+
+#include <stdlib.h>
+#include <assert.h>
+#include <librnd/core/compat_lrealpath.h>
+#include <librnd/core/compat_fs.h>
+#include <genvector/gds_char.h>
+
+#include "util_path.h"
+
+char *csch_relative_path_files(const char *pth, const char *relto)
+{
+	char *freeme1 = NULL, *freeme2 = NULL;
+	const char *s, *s1, *s2;
+	int offs, commsep = -1;
+	gds_t res = {0};
+	
+
+	/* make sure both inputs are full paths */
+	if (!rnd_is_path_abs(pth))
+		pth = freeme1 = rnd_lrealpath(pth);
+	if (!rnd_is_path_abs(relto))
+		relto = freeme2 = rnd_lrealpath(relto);
+
+	/* calculate common part */
+	for(offs = 0, s1 = pth, s2 = relto; *s1 == *s2; s1++, s2++, offs++)
+		if ((*s1 == '/') && (*s2 == '/'))
+			commsep = offs;
+
+	assert(commsep >= 0); /* both paths are absolute, worst case first char match */
+
+	/* add all the ../ */
+	for(s = relto+commsep+1; *s != '\0'; s++) {
+		if ((s[0] == '/') && (s[1] != '/'))
+			gds_append_str(&res, "../");
+	}
+
+	/* append partial path to dest file */
+	gds_append_str(&res, pth+commsep+1);
+
+	free(freeme1);
+	free(freeme2);
+	return res.array;
+}
Index: trunk/src/libcschem/util_path.h
===================================================================
--- trunk/src/libcschem/util_path.h	(nonexistent)
+++ trunk/src/libcschem/util_path.h	(revision 6721)
@@ -0,0 +1,7 @@
+/* Allocate a new string and store a path of pth relative to relto, assuming
+   both path and relto are files. For example if
+   path=/home/foo/bar/baz.pcb and relto=/home/foo/heh.txt, the result is
+   bar/baz.pcb; if they are swapped the result is  ../heh.txt */
+char *csch_relative_path_files(const char *pth, const char *relto);
+
+