Index: trunk/scconfig/Rev.h
===================================================================
--- trunk/scconfig/Rev.h	(revision 31763)
+++ trunk/scconfig/Rev.h	(revision 31764)
@@ -1 +1 @@
-static const int myrev = 31763;
+static const int myrev = 31764;
Index: trunk/scconfig/Rev.tab
===================================================================
--- trunk/scconfig/Rev.tab	(revision 31763)
+++ trunk/scconfig/Rev.tab	(revision 31764)
@@ -1,4 +1,4 @@
-31763	configure	new plugin: formula, for impedance calculations
+31764	configure	new plugin: formula, for impedance calculations
 31708	configure	query plugin: move the advanced search dialog from dialogs plugin to query to better access of internals
 31623	configure	query plugin: net length calculations
 31519	configure	io_tedax drc block upgrade for drc_query
Index: trunk/src_plugins/lib_formula/Plug.tmpasm
===================================================================
--- trunk/src_plugins/lib_formula/Plug.tmpasm	(revision 31763)
+++ trunk/src_plugins/lib_formula/Plug.tmpasm	(revision 31764)
@@ -2,6 +2,7 @@
 put /local/pcb/mod/OBJS [@
 	$(PLUGDIR)/lib_formula/lib_formula.o
 	$(PLUGDIR)/lib_formula/impedance.o
+	$(PLUGDIR)/lib_formula/bisect.o
 @]
 
 switch /local/pcb/lib_formula/controls
Index: trunk/src_plugins/lib_formula/bisect.c
===================================================================
--- trunk/src_plugins/lib_formula/bisect.c	(nonexistent)
+++ trunk/src_plugins/lib_formula/bisect.c	(revision 31764)
@@ -0,0 +1,98 @@
+/*
+ *                            COPYRIGHT
+ *
+ *  pcb-rnd, interactive printed circuit board design
+ *  Copyright (C) 2020 Tibor 'Igor2' Palinkas
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; 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/pcb-rnd
+ *    lead developer: http://repo.hu/projects/pcb-rnd/contact.html
+ *    mailing list: pcb-rnd (at) list.repo.hu (send "subscribe")
+ */
+
+#include "config.h"
+#include <librnd/core/actions.h>
+#include "bisect.h"
+
+#define CALL(value) \
+do { \
+	argv[specn].val.nat_double = value; \
+	ferr = rnd_actionv_(f, &r, argc-2, argv+2); \
+	if (ferr != 0) { \
+		rnd_message(RND_MSG_ERROR, "formula_bisect: '%s' returned error on value %f\n", actname, value); \
+		return -1; \
+	} \
+	fgw_arg_conv(&rnd_fgw, res, FGW_DOUBLE); \
+	if (res->type != FGW_DOUBLE) { \
+		rnd_message(RND_MSG_ERROR, "formula_bisect: '%s' returned not-a-number on value %f\n", actname, value); \
+		return -1; \
+	} \
+} while(0)
+
+const char pcb_acts_formula_bisect[] = "formula_bisect(action, res, args)";
+const char pcb_acth_formula_bisect[] = "Find the value for exactly one of the arguments that produces the expected result. One argument must be a string with type:min:max:precision, the rest of the arguments and res must be numeric.";
+fgw_error_t pcb_act_formula_bisect(fgw_arg_t *res, int argc, fgw_arg_t *argv)
+{
+	const char *actname, *spec;
+	double target, min, max, err;
+	fgw_arg_t r;
+	int n, specn = 0;
+	const fgw_func_t *f;
+	fgw_error_t ferr;
+
+	RND_ACT_CONVARG(1, FGW_KEYWORD, formula_bisect, actname = argv[1].val.str);
+	RND_ACT_CONVARG(2, FGW_KEYWORD, formula_bisect, target = argv[2].val.nat_double);
+	for(n = 3; n < argc; n++) {
+		if (((argv[n].type & FGW_STR) == FGW_STR) && (strchr(argv[n].val.str, ':') != NULL)) {
+			if (specn > 0) {
+				rnd_message(RND_MSG_ERROR, "formula_bisect: only one argument can be variable; the two are %d and %d now\n", specn, n);
+				return FGW_ERR_ARG_CONV;
+			}
+			else
+				specn = n;
+		}
+	}
+
+	if (specn < 0) {
+		rnd_message(RND_MSG_ERROR, "formula_bisect: one argument needs to be a variable specification string\n");
+		return FGW_ERR_ARG_CONV;
+	}
+
+	f = rnd_act_lookup(actname);
+	if (f == NULL) {
+		rnd_message(RND_MSG_ERROR, "formula_bisect: no such action: %s\n", actname);
+		return FGW_ERR_ARG_CONV;
+	}
+
+
+	spec = strchr(argv[specn].val.str, ':');
+	if (sscanf(spec+1, "%lf:%lf:%lf", &min, &max, &err) != 3) {
+		rnd_message(RND_MSG_ERROR, "formula_bisect: invalid range spec: '%s'\n", spec);
+		return FGW_ERR_ARG_CONV;
+	}
+
+
+	fgw_arg_free(&rnd_fgw, &argv[specn]);
+	argv[specn].type = FGW_DOUBLE;
+
+	CALL(min);
+	CALL(max);
+
+
+	return 0;
+}
+
Index: trunk/src_plugins/lib_formula/bisect.h
===================================================================
--- trunk/src_plugins/lib_formula/bisect.h	(nonexistent)
+++ trunk/src_plugins/lib_formula/bisect.h	(revision 31764)
@@ -0,0 +1,4 @@
+extern const char pcb_acts_formula_bisect[];
+extern const char pcb_acth_formula_bisect[];
+fgw_error_t pcb_act_formula_bisect(fgw_arg_t *res, int argc, fgw_arg_t *argv);
+
Index: trunk/src_plugins/lib_formula/lib_formula.c
===================================================================
--- trunk/src_plugins/lib_formula/lib_formula.c	(revision 31763)
+++ trunk/src_plugins/lib_formula/lib_formula.c	(revision 31764)
@@ -30,6 +30,7 @@
 #include <librnd/core/plugins.h>
 
 #include "impedance.h"
+#include "bisect.h"
 
 int pplg_check_ver_lib_formula(int ver_needed) { return 0; }