Counter expressions (#3534)

* Add peglib

* - Add expression engine
- Take an expression when setting a counter

* Shift + Click = Middleclick for counters

* minor cleanup for clangify

Signed-off-by: Zach Halpern <ZaHalpern+github@gmail.com>

* Added tip entry

common/expression.cpp

@@ -0,0 +1,108 @@
+#include "expression.h"
+#include "./lib/peglib.h"
+
+#include <QByteArray>
+#include <QString>
+#include <cmath>
+#include <functional>
+
+peg::parser math(R"(
+    EXPRESSION   <-  P0
+    P0           <-  P1 (P1_OPERATOR P1)*
+    P1           <-  P2 (P2_OPERATOR P2)*
+    P2           <-  P3 (P3_OPERATOR P3)*
+    P3           <-  NUMBER / FUNCTION / VARIABLE / '(' P0 ')'
+
+    P1_OPERATOR  <-  < [-+] >
+    P2_OPERATOR  <-  < [/*] >
+    P3_OPERATOR  <-  < '^' >
+
+    NUMBER       <-  < '-'? [0-9]+ >
+    NAME         <-  < [a-z][a-z0-9]* >
+    VARIABLE     <-  < [x] >
+    FUNCTION     <-  NAME '(' EXPRESSION ( [,\n] EXPRESSION )* ')'
+
+    %whitespace  <-  [ \t\r]*
+    )");
+
+QMap<QString, std::function<double(double)>> *default_functions = nullptr;
+
+Expression::Expression(double initial) : value(initial)
+{
+    if (default_functions == nullptr) {
+        default_functions = new QMap<QString, std::function<double(double)>>();
+        default_functions->insert("sin", [](double a) { return sin(a); });
+        default_functions->insert("cos", [](double a) { return cos(a); });
+        default_functions->insert("tan", [](double a) { return tan(a); });
+        default_functions->insert("sqrt", [](double a) { return sqrt(a); });
+        default_functions->insert("log", [](double a) { return log(a); });
+        default_functions->insert("log10", [](double a) { return log(a); });
+        default_functions->insert("trunc", [](double a) { return trunc(a); });
+        default_functions->insert("abs", [](double a) { return abs(a); });
+
+        default_functions->insert("floor", [](double a) { return floor(a); });
+        default_functions->insert("ceil", [](double a) { return ceil(a); });
+        default_functions->insert("round", [](double a) { return round(a); });
+        default_functions->insert("trunc", [](double a) { return trunc(a); });
+    }
+    fns = QMap<QString, std::function<double(double)>>(*default_functions);
+}
+
+double Expression::eval(const peg::Ast &ast)
+{
+    const auto &nodes = ast.nodes;
+    if (ast.name == "NUMBER") {
+        return stod(ast.token);
+    } else if (ast.name == "FUNCTION") {
+        QString name = QString::fromStdString(nodes[0]->token);
+        if (!fns.contains(name))
+            return 0;
+        return fns[name](eval(*nodes[1]));
+    } else if (ast.name == "VARIABLE") {
+        return value;
+    } else if (ast.name[0] == 'P') {
+        double result = eval(*nodes[0]);
+        for (int i = 1; i < nodes.size(); i += 2) {
+            double arg = eval(*nodes[i + 1]);
+            char operation = nodes[i]->token[0];
+            switch (operation) {
+                case '+':
+                    result += arg;
+                    break;
+                case '-':
+                    result -= arg;
+                    break;
+                case '*':
+                    result *= arg;
+                    break;
+                case '/':
+                    result /= arg;
+                    break;
+                case '^':
+                    result = pow(result, arg);
+                    break;
+                default:
+                    result = 0;
+                    break;
+            }
+        }
+        return result;
+    } else {
+        return -1;
+    }
+}
+
+double Expression::parse(const QString &expr)
+{
+    QByteArray ba = expr.toLocal8Bit();
+
+    math.enable_ast();
+
+    std::shared_ptr<peg::Ast> ast;
+    if (math.parse(ba.data(), ast)) {
+        ast = peg::AstOptimizer(true).optimize(ast);
+        return eval(*ast);
+    }
+
+    return 0;
+}