Exact division algorithm is now in BigDecimal::dividedBy()

BigRational::toBigDecimal() is now really just a proxy method to BigDecimal::dividedBy().

src/BigDecimal.php

@@ -150,7 +150,31 @@ final class BigDecimal extends BigNumber implements \Serializable
     {
         $that = BigDecimal::of($that);
 
-        $result = $this->toBigRational()->dividedBy($that->toBigRational())->toBigDecimal();
+        if ($that->value === '0') {
+            throw DivisionByZeroException::denominatorMustNotBeZero();
+        }
+
+        $this->scaleValues($this, $that, $a, $b);
+
+        $d = rtrim($b, '0');
+        $scale = strlen($b) - strlen($d);
+
+        $calculator = Calculator::get();
+
+        foreach ([5, 2] as $prime) {
+            for (;;) {
+                $lastDigit = (int) substr($d, -1);
+
+                if ($lastDigit % $prime !== 0) {
+                    break;
+                }
+
+                list ($d) = $calculator->div($d, (string) $prime);
+                $scale++;
+            }
+        }
+
+        $result = $this->dividedToScale($that, $scale)->stripTrailingZeros();
 
         if ($result->scale < $this->scale) {
             $result = $result->withScale($this->scale);

src/BigRational.php

@@ -271,37 +271,7 @@ final class BigRational extends BigNumber implements \Serializable
      */
     public function toBigDecimal()
     {
-        $simplified = $this->simplified();
-
-        $denominator = $simplified->denominator;
-
-        $counts = [
-            2 => 0,
-            5 => 0
-        ];
-
-        foreach ([2, 5] as $divisor) {
-            do {
-                list ($quotient, $remainder) = $denominator->quotientAndRemainder($divisor);
-
-                if ($remainderIsZero = $remainder->isZero()) {
-                    $denominator = $quotient;
-                    $counts[$divisor]++;
-                }
-            }
-            while ($remainderIsZero);
-        }
-
-        if (! $denominator->isEqualTo(1)) {
-            throw new RoundingNecessaryException('This rational number cannot be represented as a finite decimal number without rounding.');
-        }
-
-        $maxDecimalPlaces = max($counts[2], $counts[5]);
-
-        return $simplified->numerator
-            ->toBigDecimal()
-            ->dividedToScale($simplified->denominator, $maxDecimalPlaces)
-            ->stripTrailingZeros();
+        return $this->numerator->toBigDecimal()->dividedBy($this->denominator);
     }
 
     /**

tests/BigDecimalTest.php

@@ -3,6 +3,7 @@
 namespace Brick\Math\Tests;
 
 use Brick\Math\BigDecimal;
+use Brick\Math\Exception\DivisionByZeroException;
 use Brick\Math\RoundingMode;
 use Brick\Math\Exception\RoundingNecessaryException;
 
@@ -633,17 +634,20 @@ class BigDecimalTest extends AbstractTestCase
      *
      * @param string|number $number   The number to divide.
      * @param string|number $divisor  The divisor.
-     * @param string|null   $expected The expected result, or null if an exception is expected.
+     * @param string        $expected The expected result, or a class name if an exception is expected.
      */
     public function testDividedBy($number, $divisor, $expected)
     {
-        if ($expected === null) {
-            $this->setExpectedException(RoundingNecessaryException::class);
+        $number = BigDecimal::of($number);
+
+        if ($this->isException($expected)) {
+            $this->setExpectedException($expected);
         }
 
-        $actual = BigDecimal::of($number)->dividedBy($divisor);
+        $actual = $number->dividedBy($divisor);
 
-        if ($expected !== null) {
+        if (! $this->isException($expected)) {
+            $this->assertInstanceOf(BigDecimal::class, $actual);
             $this->assertSame($expected, (string) $actual);
         }
     }
@@ -657,13 +661,13 @@ class BigDecimalTest extends AbstractTestCase
             [1, 1, '1'],
             ['1.0', '1.00', '1.0'],
             [1, 2, '0.5'],
-            [1, 3, null],
+            [1, 3, RoundingNecessaryException::class],
             [1, 4, '0.25'],
             [1, 5, '0.2'],
-            [1, 6, null],
-            [1, 7, null],
+            [1, 6, RoundingNecessaryException::class],
+            [1, 7, RoundingNecessaryException::class],
             [1, 8, '0.125'],
-            [1, 9, null],
+            [1, 9, RoundingNecessaryException::class],
             [1, 10, '0.1'],
             ['1.0', 2, '0.5'],
             ['1.00', 2, '0.50'],
@@ -675,6 +679,8 @@ class BigDecimalTest extends AbstractTestCase
             ['1234.5678', '4', '308.64195'],
             ['1234.5678', '8', '154.320975'],
             ['1234.5678', '6.4', '192.90121875'],
+            ['123', '0', DivisionByZeroException::class],
+            [-789, '0.0', DivisionByZeroException::class],
         ];
     }