remove dependency on gmp extensions (but use them if available)

composer.json

@@ -3,8 +3,7 @@
     "description": "a generative testing library",
     "license": "BSD-3-Clause",
     "require": {
-        "php-64bit": ">=5.5.0",
-        "ext-gmp": "*"
+        "php-64bit": ">=5.5.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^4.8"

src/QCheck/Random.php

@@ -21,6 +21,7 @@ public static function rshiftu($a, $b)
         if ($b == 0) {
             return $a;
         }
+
         return ($a >> $b) & ~(1 << 63 >> ($b - 1));
     }
     public static function mask($val)
@@ -40,17 +41,57 @@ public function setSeed($seed)
     }
     protected function next($bits)
     {
-        $temp = gmp_intval(gmp_mul($this->seed, self::MULTIPLIER));
+        $temp = self::general_intval(self::general_int_mul($this->seed, self::MULTIPLIER));
         $this->seed = self::mask($temp + self::ADDEND);
+
         return self::i32(self::rshiftu($this->seed, (48 - $bits)));
     }
     public function nextDouble()
     {
         return (($this->next(26) << 27) + $this->next(27))
-            / (double)(1 << 53);
+            / (double) (1 << 53);
     }
     public function nextInt()
     {
         return $this->next(32);
     }
+
+    public function general_int_mul($a, $b) {
+      if (function_exists("gmp_mul")) return gmp_mul($a, $b);
+      return self::int_mul($a, $b);
+    }
+
+    public function general_intval($a) {
+      if (function_exists("gmp_intval")) return gmp_intval($a);
+      return intval($a);
+    }
+
+    // multiplication with only shifts and ands
+    // does Java/C/Go-like overflow
+    // http://stackoverflow.com/questions/4456442/multiplication-of-two-integers-using-bitwise-operators
+    public function int_mul($a, $b)
+    {
+        $result = 0;
+        while ($b != 0) {
+            // Iterate the loop till b==0
+        if ($b & 01) {                // is $b odd?
+          $result = self::int_add($result, $a); // int_add result
+        }
+            $a <<= 1;               // Left shifting the value contained in 'a' by 1
+                                    // multiplies a by 2 for each loop
+        $b >>= 1;                   // Right shifting the value contained in 'b' by 1.
+        }
+
+        return $result;
+    }
+
+    // addition with only shifts and ands
+    public function int_add($x, $y)
+    {
+        if ($y == 0) {
+            return $x;
+        } else {
+            return self::int_add($x ^ $y, ($x & $y) << 1);
+        }
+    }
 }