Fix on the tan function when the value is undefined like for tan(pi/2)

Author: codisart

src/Decimal.php

@@ -742,9 +742,16 @@ public function cos($scale = null) {
      * @return Decimal tan($this)
      */
     public function tan($scale = null) {
-        return $this->sin($scale + 2)
-            ->div($this->cos($scale + 2))
-            ->floor($scale);
+	    $cos = $this->cos($scale + 2);
+	    if ($cos->isZero()) {
+	        throw new \DomainException(
+	            "The tangent of this 'angle' is undefined."
+	        );
+	    }
+
+	    return $this->sin($scale + 2)
+	        ->div($cos)
+	        ->floor($scale);
     }
 
     public function hasSameSign(Decimal $b) {

tests/Decimal/DecimalTanTest.php

@@ -1,6 +1,7 @@
 <?php
 
 use Litipk\BigNumbers\Decimal as Decimal;
+use \Litipk\BigNumbers\DecimalConstants as DecimalConstants;
 
 /**
  * @group tan
@@ -26,4 +27,19 @@ public function testSimple($nr, $answer, $digits)
         $tanX = $x->tan($digits);
         $this->assertTrue(Decimal::fromString($answer)->equals($tanX));
     }
+    
+    public function testTanPiTwoDiv()
+    {    	
+        $PI  = DecimalConstants::PI();
+        $two = Decimal::fromInteger(2);
+        $PiDividedByTwo = $PI->div($two);
+
+        $catched = false;
+        try {
+            $PiDividedByTwo->tan();
+        } catch (\DomainException $e) {
+            $catched = true;
+        }
+        $this->assertTrue($catched);
+    }
 }