added half-even rounding (#34)

* added half-even rounding

Author: aywan

src/BCMathExtended/BC.php

@@ -630,4 +630,33 @@ public static function bitXor(string $leftOperand, string $rightOperand): string
     {
         return self::bitOperatorHelper($leftOperand, $rightOperand, self::BIT_OPERATOR_XOR);
     }
+
+    public static function roundHalfEven(string $number, int $precision = 0): string
+    {
+        $number = self::convertScientificNotationToString($number);
+        if (! self::checkIsFloat($number)) {
+            return self::checkNumber($number);
+        }
+
+        $precessionPos = strpos($number, '.') + $precision + 1;
+        if (strlen($number) <= $precessionPos) {
+            return self::round($number, $precision);
+        }
+
+        if ($number[$precessionPos] !== '5') {
+            return self::round($number, $precision);
+        }
+
+        $isPrevEven = $number[$precessionPos - 1] === '.'
+            ? (int)$number[$precessionPos - 2] % 2 === 0
+            : (int)$number[$precessionPos - 1] % 2 === 0
+        ;
+        $isNegative = self::isNegative($number);
+
+        if ($isPrevEven === $isNegative) {
+            return self::roundUp($number, $precision);
+        }
+
+        return self::roundDown($number, $precision);
+    }
 }

tests/Unit/BCTest.php

@@ -284,6 +284,47 @@ public function shouldRound($expected, $number, $precision = 0): void
         self::assertSame($expected, BC::round((string)$number, $precision));
     }
 
+    public function roundHalfEvenProvider(): array
+    {
+        return [
+            ['2', '1.8'],
+            ['2', '1.5'],
+            ['1', '1.2'],
+            ['1', '0.8'],
+            ['0', '0.5'],
+            ['0', '0.2'],
+            ['-0', '-0.2'],
+            ['0', '-0.5'],
+            ['-1', '-0.8'],
+            ['-1', '-1.2'],
+            ['-2', '-1.5'],
+            ['-2', '-1.8'],
+            ['-2.35', '-2.35', 2],
+            ['-2.4', '-2.35', 1],
+            ['2.4', '2.35', 1],
+            ['0', '0.005', 2],
+            ['0.02', '0.015', 2],
+            ['0.02', '0.025', 2],
+            ['0.04', '0.035', 2],
+            ['0.04', '0.045', 2],
+            ['0.06', '0.055', 2],
+            ['0.06', '0.065', 2],
+            ['0.08', '0.075', 2],
+            ['0.08', '0.085', 2],
+        ];
+    }
+
+    /**
+     * @test
+     * @dataProvider roundHalfEvenProvider
+     * @param string $expected
+     * @param string $number
+     * @param int $precision
+     */
+    public function shouldRoundHalfEven(string $expected, string $number, int $precision = 0): void
+    {
+        self::assertSame($expected, BC::roundHalfEven($number, $precision));
+    }
 
     public function randProvider(): array
     {