Works! (#161)

* use log1p when appropriate
* Fix left bitshift

src/Probability/Distribution/Continuous/StudentT.php

@@ -80,7 +80,7 @@ public function pdf(float $t): float
 	        $l_x2n = log(1 + $x2n) / 2;
 	        $u = $ν * $l_x2n;
         } else {
-	        $l_x2n = log($x2n + 1) / 2;
+	        $l_x2n = log1p($x2n) / 2;
 	        $u = -1* self::bd0($ν / 2, ($ν + $t**2) / 2) + $t**2 / 2;
         }
 
@@ -237,7 +237,7 @@ static function bd0(float $x, float $np)
 	        for ($j = 1; $j < 1000; $j++) {
 	            $ej *= $v;
 	            $stemp = $s;
-	            $s += $ej / (($j *= 2) + 1); // Does $j get doubled here?
+	            $s += $ej / (($j * 2) + 1);
 	            if ($s == $stemp) {
                     return $s;
 	            }
@@ -271,7 +271,7 @@ static function stirlerr (float $n)
 	        0.03316287351993628748511048, /* 2.5 */
 	        0.02767792568499833914878929, /* 3.0 */
 	        0.02374616365629749597132920, /* 3.5 */
-	        0.02079067210376509311152277, /* 4.0 */
+            0.02079067210376509311152277, /* 4.0 */
             0.01848845053267318523077934, /* 4.5 */
             0.01664469118982119216319487, /* 5.0 */
 	        0.01513497322191737887351255, /* 5.5 */