Add addHalf()/subHalf() functions

src/Carbon.php

@@ -19,14 +19,34 @@ class Carbon extends CarbonBase
             case 'half':
                 return (int) ceil($this->month / static::MONTHS_PER_HALF);
 
-	       case 'quarter_string':
-		       return sprintf('%dQ%d',$this->year,$this->quarter);
+           case 'quarter_string':
+               return sprintf('%dQ%d',$this->year,$this->quarter);
 
             default:
                 return parent::__get($name);
        }
     }
 
+    public function addHalf(): self
+    {
+        return $this->addHalves(1);
+    }
+
+    public function addHalves(int $unit): self
+    {
+        return $this->addQuarters(2*$unit);
+    }
+
+    public function subHalf(): self
+    {
+        return $this->subHalves(1);
+    }
+
+    public function subHalves(int $unit): self
+    {
+        return $this->subQuarters(2*$unit);
+    }
+
     /**
      * Modify to the first occurrence of a given day of the week
      * in the current quarter. If no dayOfWeek is provided, modify to the