Add BigInteger::gcd()

This computes the greatest common divisor of two large integers.
brick · Jun 11, 2015 · 4f4b953 · 4f4b953
1 parent 1f577af
commit 4f4b953
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diff --git a/src/BigInteger.php b/src/BigInteger.php
@@ -377,6 +377,30 @@ public function power($exponent)
         return new BigInteger(Calculator::get()->pow($this->value, $exponent));
     }
 
+    /**
+     * Returns the greatest common divisor of this number and the given one.
+     *
+     * The GCD is always positive.
+     *
+     * @param BigInteger|int|string $that
+     *
+     * @return BigInteger
+     */
+    public function gcd($that)
+    {
+        $that = BigInteger::of($that);
+
+        if ($that->isZero()) {
+            return $this->abs();
+        }
+
+        if ($this->isZero()) {
+            return $that->abs();
+        }
+
+        return $that->gcd($this->remainder($that));
+    }
+
     /**
      * Returns the absolute value of this number.
      *

diff --git a/tests/BigIntegerTest.php b/tests/BigIntegerTest.php
@@ -1205,6 +1205,109 @@ public function providerPowerWithInvalidExponentThrowsException()
         ];
     }
 
+    /**
+     * @dataProvider providerGcd
+     *
+     * @param string $a   The first number.
+     * @param string $b   The second number.
+     * @param string $gcd The expected GCD.
+     */
+    public function testGcd($a, $b, $gcd)
+    {
+        $a = BigInteger::of($a);
+        $b = BigInteger::of($b);
+
+        $this->assertBigIntegerEquals($gcd, $a->gcd($b));
+    }
+
+    /**
+     * @return \Generator
+     */
+    public function providerGcd()
+    {
+        $tests = [
+            ['0', '0', '0'],
+
+            ['123456789123456789123456789123456789', '0', '123456789123456789123456789123456789'],
+            ['123456789123456789123456789123456789', '1', '1'],
+            ['123456789123456789123456789123456789', '2', '1'],
+            ['123456789123456789123456789123456789', '3', '3'],
+            ['123456789123456789123456789123456789', '4', '1'],
+            ['123456789123456789123456789123456789', '5', '1'],
+            ['123456789123456789123456789123456789', '6', '3'],
+            ['123456789123456789123456789123456789', '7', '7'],
+            ['123456789123456789123456789123456789', '8', '1'],
+            ['123456789123456789123456789123456789', '9', '9'],
+            ['123456789123456789123456789123456789', '10', '1'],
+            ['123456789123456789123456789123456789', '11', '11'],
+            ['123456789123456789123456789123456789', '12', '3'],
+            ['123456789123456789123456789123456789', '13', '13'],
+            ['123456789123456789123456789123456789', '14', '7'],
+            ['123456789123456789123456789123456789', '15', '3'],
+            ['123456789123456789123456789123456789', '16', '1'],
+            ['123456789123456789123456789123456789', '17', '1'],
+            ['123456789123456789123456789123456789', '18', '9'],
+            ['123456789123456789123456789123456789', '19', '19'],
+            ['123456789123456789123456789123456789', '20', '1'],
+            ['123456789123456789123456789123456789', '100', '1'],
+            ['123456789123456789123456789123456789', '101', '101'],
+            ['123456789123456789123456789123456789', '102', '3'],
+            ['123456789123456789123456789123456789', '103', '1'],
+            ['123456789123456789123456789123456789', '104', '13'],
+            ['123456789123456789123456789123456789', '105', '21'],
+            ['123456789123456789123456789123456789', '985', '1'],
+            ['123456789123456789123456789123456789', '986', '1'],
+            ['123456789123456789123456789123456789', '987', '21'],
+            ['123456789123456789123456789123456789', '988', '247'],
+            ['123456789123456789123456789123456789', '989', '1'],
+            ['123456789123456789123456789123456789', '990', '99'],
+            ['123456789123456789123456789123456789', '10010', '1001'],
+            ['123456789123456789123456789123456789', '10017', '63'],
+            ['123456789123456789123456789123456789', '10089', '171'],
+            ['123456789123456789123456789123456789', '10098', '99'],
+            ['123456789123456789123456789123456789', '100035', '2223'],
+            ['123456789123456789123456789123456789', '1000065', '627'],
+            ['123456789123456789123456789123456789', '10000068', '39'],
+            ['123456789123456789123456789123456789', '10001222', '7777'],
+            ['123456789123456789123456789123456789', '10001277', '24453'],
+            ['123456789123456789123456789123456789', '100005258', '157737'],
+            ['123456789123456789123456789123456789', '100010001', '2702973'],
+            ['123456789123456789123456789123456789', '100148202', '50074101'],
+            ['123456789123456789123456789123456789', '100478469', '14354067'],
+            ['123456789123456789123456789123456789', '123456789140121129', '8249681517'],
+            ['123456789123456789123456789123456789', '123456789150891631', '1385459521'],
+            ['123456789123456789123456789123456789', '123456789192058322', '6928754833'],
+            ['123456789123456789123456789123456789', '123456789202361433', '1992342261'],
+            ['123456789123456789123456789123456789', '999456789162772941', '20786264499'],
+            ['123456789123456789123456789123456789', '999456789176548074', '2345678991'],
+            ['123456789123456789123456789123456789', '999456789188938248', '2372170689'],
+
+            ['88888777776666655555444443333322222111110000099999', '100000000011886128', '8252579097'],
+            ['88888777776666655555444443333322222111110000099999', '100000000013330403', '1162443303'],
+            ['88888777776666655555444443333322222111110000099999', '100000000020221920', '2470053077'],
+            ['88888777776666655555444443333322222111110000099999', '100000000031937250', '3970893353'],
+            ['88888777776666655555444443333322222111110000099999', '100000000043341848', '1102420413'],
+            ['88888777776666655555444443333322222111110000099999', '100000000047565681', '1212240071'],
+            ['88888777776666655555444443333322222111110000099999', '100000000065586124', '1172302873'],
+            ['88888777776666655555444443333322222111110000099999', '100000000068684846', '1051734417'],
+            ['88888777776666655555444443333322222111110000099999', '100000000068736887', '2423071539'],
+        ];
+
+        foreach ($tests as list ($a, $b, $gcd)) {
+            yield [$a, $b, $gcd];
+            yield [$b, $a, $gcd];
+
+            yield [$a, "-$b", $gcd];
+            yield [$b, "-$a", $gcd];
+
+            yield ["-$a", $b, $gcd];
+            yield ["-$b", $a, $gcd];
+
+            yield ["-$a", "-$b", $gcd];
+            yield ["-$b", "-$a", $gcd];
+        }
+    }
+
     /**
      * @dataProvider providerAbs
      *