mp-equation: add pre-defined physical constants

This adds some fundamental physical constants:
- Velocity of Light "c₀", 299,792,458 m/s
- Magnetic constant, "μ₀", 1.2566370614×10⁻ N/A²
- Electric constant, "ε₀", 8.85418782×10⁻¹² s⁴A²/m³kg
- Newtonian constant of gravitation, "G",  6.67408×10⁻¹¹ m³/(s²kg)
- Planck constant, "h", 6.62607004×10⁻³⁴ m²kg/s
- Elementary charge, "ｅ", 1.6021766208(98)×10⁻¹⁹ C
- Electron mass, "mₑ", 9.10938356×10⁻³¹ kg
- Proton mass, "mₚ", 1.672621898(21)×10⁻²⁷ kg
- Avogrado constant, "Nₐ", 6.02214086×10²³ mol⁻¹

They are taken from https://en.wikipedia.org/wiki/Physical_constant#Universal_constants
To insert them one would enter the corresponding symbol or use the gui.
They are set to a MPNumber from string.

3 files changed, 148 insertions, 6 deletions

diff --git a/src/buttons-advanced.ui b/src/buttons-advanced.ui
index c668b25..df93b8d 100644
--- a/src/buttons-advanced.ui
+++ b/src/buttons-advanced.ui
@@ -766,8 +766,8 @@
             </child>
           </object>
           <packing>
-            <property name="left_attach">9</property>
-            <property name="top_attach">4</property>
+            <property name="left_attach">10</property>
+            <property name="top_attach">0</property>
           </packing>
         </child>
         <child>
@@ -861,7 +861,7 @@
             <signal name="clicked" handler="button_cb" swapped="no"/>
           </object>
           <packing>
-            <property name="left_attach">10</property>
+            <property name="left_attach">9</property>
             <property name="top_attach">4</property>
           </packing>
         </child>
@@ -949,7 +949,46 @@
           </packing>
         </child>
         <child>
-          <placeholder/>
+          <object class="GtkButton" id="calc_const_button">
+            <property name="visible">True</property>
+            <property name="can_focus">True</property>
+            <property name="receives_default">True</property>
+            <signal name="clicked" handler="const_cb" swapped="no"/>
+            <child>
+              <object class="GtkBox" id="hbox3">
+                <property name="visible">True</property>
+                <property name="can_focus">False</property>
+                <child>
+                  <object class="GtkLabel">
+                    <property name="visible">True</property>
+                    <property name="can_focus">False</property>
+                    <property name="label" translatable="yes">const</property>
+                  </object>
+                  <packing>
+                    <property name="expand">True</property>
+                    <property name="fill">True</property>
+                    <property name="position">0</property>
+                  </packing>
+                </child>
+                <child>
+                  <object class="GtkArrow" id="arrow3">
+                    <property name="visible">True</property>
+                    <property name="can_focus">False</property>
+                    <property name="arrow_type">down</property>
+                  </object>
+                  <packing>
+                    <property name="expand">False</property>
+                    <property name="fill">True</property>
+                    <property name="position">1</property>
+                  </packing>
+                </child>
+              </object>
+            </child>
+          </object>
+          <packing>
+            <property name="left_attach">10</property>
+            <property name="top_attach">4</property>
+          </packing>
         </child>
       </object>
     </child>
diff --git a/src/math-buttons.c b/src/math-buttons.c
index 50b15a7..22d8570 100644
--- a/src/math-buttons.c
+++ b/src/math-buttons.c
@@ -45,6 +45,7 @@ struct MathButtonsPrivate
     GtkWidget *shift_left_menu, *shift_right_menu;
 
     GtkWidget *function_menu;
+    GtkWidget *const_menu;
 
     GList *superscript_toggles;
     GList *subscript_toggles;
@@ -125,6 +126,9 @@ static ButtonData button_data[] = {
     {"function",           NULL, FUNCTION,
       /* Tooltip for the additional functions button */
       N_("Additional Functions")},
+    {"const",           NULL, FUNCTION,
+      /* Tooltip for the additional constant button */
+      N_("Additional constants")},
     {"x_pow_y",            "^", FUNCTION,
       /* Tooltip for the exponent button */
       N_("Exponent [^ or **]")},
@@ -1021,6 +1025,63 @@ function_cb(GtkWidget *widget, MathButtons *buttons)
     popup_button_menu(widget, GTK_MENU(buttons->priv->function_menu));  
 }
 
+static void
+insert_const_cb(GtkWidget *widget, MathButtons *buttons)
+{
+    math_equation_insert(buttons->priv->equation, g_object_get_data(G_OBJECT(widget), "const"));
+}
+
+
+void const_cb(GtkWidget *widget, MathButtons *buttons);
+G_MODULE_EXPORT
+void
+const_cb(GtkWidget *widget, MathButtons *buttons)
+{
+    if (!buttons->priv->const_menu) {
+        gint i;
+        GtkWidget *menu;
+        struct 
+        {
+            gchar *name, *constant;
+        } constants[] = 
+        {
+            { /* Tooltip for the c₀ component button */
+              N_("Velocity of Light"), "c₀" },
+            { /* Tooltip for the μ₀ component button */
+              N_("Magnetic constant"), "μ₀" },
+            { /* Tooltip for the ε₀ button */
+              N_("Electric constant"), "ε₀" },
+            { /* Tooltip for the G button */
+              N_("Newtonian constant of gravitation"), "G" },
+            { /* Tooltip for the h button */
+              N_("Planck constant"), "h" },
+            { /* Tooltip for the ｅ button */
+              N_("Elementary charge"), "ｅ" },
+            { /* Tooltip for the mₑ button */
+              N_("Electron mass"), "mₑ" },
+            { /* Tooltip for the mₚ button */
+              N_("Proton mass"), "mₚ" },
+            { /* Tooltip for the Nₐ button */
+              N_("Avogrado constant"), "Nₐ" },
+            { NULL, NULL }
+        };
+
+        menu = buttons->priv->const_menu = gtk_menu_new();
+        gtk_menu_set_reserve_toggle_size(GTK_MENU(menu), FALSE);
+
+        for (i = 0; constants[i].name != NULL; i++) {
+            GtkWidget *item;
+          
+            item = gtk_menu_item_new_with_label(_(constants[i].name));
+            g_object_set_data(G_OBJECT(item), "const", g_strdup(constants[i].constant));
+            gtk_menu_shell_append(GTK_MENU_SHELL(menu), item);
+            g_signal_connect(item, "activate", G_CALLBACK(insert_const_cb), buttons);
+            gtk_widget_show(item);
+        }
+    }
+
+    popup_button_menu(widget, GTK_MENU(buttons->priv->const_menu));  
+}
 
 void factorize_cb(GtkWidget *widget, MathButtons *buttons);
 G_MODULE_EXPORT
diff --git a/src/mp-equation.c b/src/mp-equation.c
index b80408e..fd3ea5a 100644
--- a/src/mp-equation.c
+++ b/src/mp-equation.c
@@ -18,7 +18,19 @@ static int
 variable_is_defined(ParserState *state, const char *name)
 {
     /* FIXME: Make more generic */
-    if (strcmp(name, "e") == 0 || strcmp(name, "i") == 0 || strcmp(name, "π") == 0 || strcmp(name, "pi") == 0)
+    if (strcmp(name, "e") == 0 ||
+        strcmp(name, "i") == 0 ||
+        strcmp(name, "π") == 0 ||
+        strcmp(name, "pi") == 0 ||
+        strcmp(name, "c₀") == 0 ||
+        strcmp(name, "μ₀") == 0 ||
+        strcmp(name, "ε₀") == 0 ||
+        strcmp(name, "G") == 0 ||
+        strcmp(name, "h") == 0 ||
+        strcmp(name, "ｅ") == 0 ||
+        strcmp(name, "mₑ") == 0 ||
+        strcmp(name, "mₚ") == 0 ||
+        strcmp(name, "Nₐ") == 0)
         return 1;
     if (state->options->variable_is_defined)
         return state->options->variable_is_defined(name, state->options->callback_data);
@@ -37,6 +49,24 @@ get_variable(ParserState *state, const char *name, MPNumber *z)
         mp_get_i(z);
     else if (strcmp(name, "π") == 0 || strcmp(name, "pi") == 0)
         mp_get_pi(z);
+    else if (strcmp(name, "c₀") == 0)
+        mp_set_from_string("299792458", 10, z); /* velocity of light */
+    else if (strcmp(name, "μ₀") == 0)
+        mp_set_from_string("0.0000012566370614", 10, z); /* magnetic constant */
+    else if (strcmp(name, "ε₀") == 0)
+        mp_set_from_string("0.000000000008854187817", 10, z); /* electric constant */
+    else if (strcmp(name, "G") == 0)
+        mp_set_from_string("0.0000000000667310", 10, z); /* Newtonian constant of gravitation */
+    else if (strcmp(name, "h") == 0)
+        mp_set_from_string("0.000000000000000000000000000000000662606876", 10, z); /* Planck constant */
+    else if (strcmp(name, "ｅ") == 0)
+        mp_set_from_string("0.0000000000000000001602176462", 10, z); /* elementary charge */
+    else if (strcmp(name, "mₑ") == 0)
+        mp_set_from_string("0.000000000000000000000000000000910938188", 10, z); /* electron mass */
+    else if (strcmp(name, "mₚ") == 0)
+        mp_set_from_string("0.00000000000000000000000000167262158", 10, z); /* proton mass */
+    else if (strcmp(name, "Nₐ") == 0)
+        mp_set_from_string("602214199000000000000000", 10, z); /* Avogrado constant */ 
     else if (state->options->get_variable)
         result = state->options->get_variable(name, z, state->options->callback_data);
     else
@@ -49,7 +79,19 @@ static void
 set_variable(ParserState *state, const char *name, const MPNumber *x)
 {
     // Reserved words, e, π, mod, and, or, xor, not, abs, log, ln, sqrt, int, frac, sin, cos, ...
-    if (strcmp(name, "e") == 0 || strcmp(name, "i") == 0 || strcmp(name, "π") == 0 || strcmp(name, "pi") == 0)
+    if (strcmp(name, "e") == 0 ||
+        strcmp(name, "i") == 0 ||
+        strcmp(name, "π") == 0 ||
+        strcmp(name, "pi") == 0 ||
+        strcmp(name, "c₀") == 0 ||
+        strcmp(name, "μ₀") == 0 ||
+        strcmp(name, "ε₀") == 0 ||
+        strcmp(name, "G") == 0 ||
+        strcmp(name, "h") == 0 ||
+        strcmp(name, "ｅ") == 0 ||
+        strcmp(name, "mₑ") == 0 ||
+        strcmp(name, "mₚ") == 0 ||
+        strcmp(name, "Nₐ") == 0)
         return; // FALSE
 
     if (state->options->set_variable)