Add a method to Expr.

(Split out from earlier "Eigen library integration" commit)

src/expr.cpp

@@ -430,6 +430,11 @@ bool Expr::DependsOn(hParam p) const {
 bool Expr::Tol(double a, double b) {
     return fabs(a - b) < 0.001;
 }
+
+bool Expr::IsZeroConst() const {
+    return op == Op::CONSTANT && EXACT(v == 0.0);
+}
+
 Expr *Expr::FoldConstants() {
     Expr *n = AllocExpr();
     *n = *this;

src/expr.h

@@ -73,6 +73,7 @@ public:
     void ParamsUsedList(List<hParam> *list) const;
     bool DependsOn(hParam p) const;
     static bool Tol(double a, double b);
+    bool IsZeroConst() const;
     Expr *FoldConstants();
     void Substitute(hParam oldh, hParam newh);