Keep big integer as integer instead of lossely casting to float

Closes #874
Fixes #1135

Author: PowerKiKi

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 - Formula Parser: Wrong line count for stuff like "MyOtherSheet!A:D" [#1215](https://github.com/PHPOffice/PhpSpreadsheet/issues/1215)
 - Call garbage collector after removing a column to prevent stale cached values
 - Trying to remove a column that doesn't exist deletes the latest column
+- Keep big integer as integer instead of lossely casting to float [#874](https://github.com/PHPOffice/PhpSpreadsheet/pull/874)
 
 ## [1.9.0] - 2019-08-17
 

src/PhpSpreadsheet/Cell/Cell.php

@@ -217,7 +217,7 @@ public function setValueExplicit($pValue, $pDataType)
 
                 break;
             case DataType::TYPE_NUMERIC:
-                $this->value = (float) $pValue;
+                $this->value = 0 + $pValue;
 
                 break;
             case DataType::TYPE_FORMULA:

tests/PhpSpreadsheetTests/Cell/CellTest.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Cell;
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PHPUnit\Framework\TestCase;
+
+class CellTest extends TestCase
+{
+    /**
+     * @dataProvider providerSetValueExplicit
+     *
+     * @param mixed $expected
+     * @param mixed $value
+     * @param string $dataType
+     */
+    public function testSetValueExplicit($expected, $value, string $dataType)
+    {
+        $spreadsheet = new Spreadsheet();
+        $cell = $spreadsheet->getActiveSheet()->getCell('A1');
+        $cell->setValueExplicit($value, $dataType);
+
+        self::assertSame($expected, $cell->getValue());
+    }
+
+    public function providerSetValueExplicit()
+    {
+        return require 'data/Cell/SetValueExplicit.php';
+    }
+}

tests/data/Cell/SetValueExplicit.php

@@ -0,0 +1,26 @@
+<?php
+
+use PhpOffice\PhpSpreadsheet\Cell\DataType;
+
+return [
+    [
+        1234567890123456789,
+        '01234567890123456789',
+        DataType::TYPE_NUMERIC,
+    ],
+    [
+        123.456,
+        '123.456',
+        DataType::TYPE_NUMERIC,
+    ],
+    [
+        1234567890123456789,
+        1234567890123456789,
+        DataType::TYPE_NUMERIC,
+    ],
+    [
+        123.456,
+        123.456,
+        DataType::TYPE_NUMERIC,
+    ],
+];