rational: add missing const

Change-Id: I1b7db0f3f1bf335b63488d2d3cd6d09452b0b17f
Reviewed-by: Sebastien Blin <sebastien.blin@savoirfairelinux.com>

src/rational.h

@@ -64,16 +64,16 @@ public:
     // operators are available - see operators.hpp
 
     // Arithmetic operators
-    rational operator+ (const rational& r) {
+    rational operator+ (const rational& r) const {
         return {num_*r.den_ + r.num_*den_, den_*r.den_};
     }
-    rational operator- (const rational& r) {
+    rational operator- (const rational& r) const {
         return {num_*r.den_ - r.num_*den_, den_*r.den_};
     }
-    rational operator* (const rational& r) {
+    rational operator* (const rational& r) const {
         return {num_*r.num_, den_*r.den_};
     }
-    rational operator/ (const rational& r) {
+    rational operator/ (const rational& r) const {
         return {num_*r.den_, den_*r.num_};
     }
 
@@ -117,12 +117,18 @@ public:
         bool inv = (den_ > 0) != (r.den_ > 0);
         return inv != (num_ * r.den_ < den_ * r.num_);
     }
+    bool operator> (const rational& r) const {
+        bool inv = (den_ > 0) != (r.den_ > 0);
+        return inv != (num_ * r.den_ > den_ * r.num_);
+    }
     bool operator== (const rational& r) const { return num_ * r.den_ == den_ * r.num_; }
+    bool operator!= (const rational& r) const { return num_ * r.den_ != den_ * r.num_; }
 
     // Comparison with integers
     bool operator< (I i) const { return num_ < i * den_; }
     bool operator> (I i) const { return num_ > i * den_; }
     bool operator== (I i) const { return num_ == i * den_; }
+    bool operator!= (I i) const { return num_ != i * den_; }
 private:
     I num_ {0};
     I den_ {1};