Make sure MIDI mapping extrapolation doesn't give out-of-range values.

diff --git a/midi_mapping_dialog.cpp b/midi_mapping_dialog.cpp
index 6d2159d8a079dfb0d2e49f630895d36587f6f6d8..84a24982beffd60d1a856d79634b579fb9d3be63 100644 (file)
--- a/midi_mapping_dialog.cpp
+++ b/midi_mapping_dialog.cpp
@@ -400,22 +400,29 @@ pair<int, int> MIDIMappingDialog::guess_offset(unsigned bus_idx, MIDIMappingDial
        // See if we can find a consistent offset.
        bool found_offset = false;
        int offset = 0;
+       int minimum_allowed_offset = numeric_limits<int>::min();
+       int maximum_allowed_offset = numeric_limits<int>::max();
        for (const auto &field_number_and_spinner : spinners[bus_idx]) {
                int field_number = field_number_and_spinner.first;
                QSpinBox *spinner = field_number_and_spinner.second.spinner;
                SpinnerGroup this_spinner_group = field_number_and_spinner.second.group;
+               assert(spinners[source_bus_idx].count(field_number));
+               QSpinBox *source_spinner = spinners[source_bus_idx][field_number].spinner;
+               assert(spinners[source_bus_idx][field_number].group == this_spinner_group);
 
-               if (spinner->value() == 0) {
-                       continue;
-               }
                if (spinner_group != SpinnerGroup::ALL_GROUPS &&
                    spinner_group != this_spinner_group) {
                        continue;
                }
-
-               assert(spinners[source_bus_idx].count(field_number));
-               QSpinBox *source_spinner = spinners[source_bus_idx][field_number].spinner;
-               assert(spinners[source_bus_idx][field_number].group == this_spinner_group);
+               if (spinner->value() == 0) {
+                       if (source_spinner->value() != 0) {
+                               // If the source value is e.g. 3, offset can't be less than -2 or larger than 124.
+                               // Otherwise, we'd extrapolate values outside [1..127].
+                               minimum_allowed_offset = max(minimum_allowed_offset, 1 - source_spinner->value());
+                               maximum_allowed_offset = min(maximum_allowed_offset, 127 - source_spinner->value());
+                       }
+                       continue;
+               }
                if (source_spinner->value() == 0) {
                        // The bus has a controller set that the source bus doesn't set.
                        return not_found;
@@ -435,6 +442,10 @@ pair<int, int> MIDIMappingDialog::guess_offset(unsigned bus_idx, MIDIMappingDial
                assert(false);
                return not_found;
        }
+
+       if (offset < minimum_allowed_offset || offset > maximum_allowed_offset) {
+               return not_found;
+       }
        return make_pair(source_bus_idx, offset);
 }