From 1d38fca715937e4f26371ce7e68d2e216c46be19 Mon Sep 17 00:00:00 2001
From: Stephen Sweetland <steve.sweetland@gmail.com>
Date: Thu, 25 May 2017 11:06:32 +0100
Subject: [PATCH 1/2] Update CellHelper.php

New function, try to identify a formula string
---
 src/Spout/Writer/Common/Helper/CellHelper.php | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/Spout/Writer/Common/Helper/CellHelper.php b/src/Spout/Writer/Common/Helper/CellHelper.php
index 50ead93..0bee960 100644
--- a/src/Spout/Writer/Common/Helper/CellHelper.php
+++ b/src/Spout/Writer/Common/Helper/CellHelper.php
@@ -64,6 +64,17 @@ class CellHelper
         return (gettype($value) === 'string' && $value !== '');
     }
 
+    /**
+     * Returns whether the given value looks like a formula
+     *
+     * @param $value
+     * @return bool whether the given value looks like a formula
+     */
+    public static function isFormulaString($value)
+    {
+        return (strpos($value,'=') === 0);
+    }
+
     /**
      * Returns whether the given value is numeric.
      * A numeric value is from type "integer" or "double" ("float" is not returned by gettype).

From 8ac86cb254228d9faaa9d23e9936e840ef7d4dc3 Mon Sep 17 00:00:00 2001
From: Stephen Sweetland <steve.sweetland@gmail.com>
Date: Thu, 25 May 2017 11:07:36 +0100
Subject: [PATCH 2/2] Update Worksheet.php

Supporting *writing* formulas in XLSX files is truly trivial.
---
 src/Spout/Writer/XLSX/Internal/Worksheet.php | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/Spout/Writer/XLSX/Internal/Worksheet.php b/src/Spout/Writer/XLSX/Internal/Worksheet.php
index b5a3dc7..1d853e6 100644
--- a/src/Spout/Writer/XLSX/Internal/Worksheet.php
+++ b/src/Spout/Writer/XLSX/Internal/Worksheet.php
@@ -212,8 +212,10 @@ EOD;
         $columnIndex = CellHelper::getCellIndexFromColumnIndex($cellNumber);
         $cellXML = '<c r="' . $columnIndex . $rowIndex . '"';
         $cellXML .= ' s="' . $styleId . '"';
-
-        if (CellHelper::isNonEmptyString($cellValue)) {
+        
+        if (CellHelper::isFormulaString($cellValue)) {
+            $cellXML .= '><f>'.substr($cellValue,1).'</f><v>0</v></c>'; // seriously, that's it.
+        } else if (CellHelper::isNonEmptyString($cellValue)) {
             $cellXML .= $this->getCellXMLFragmentForNonEmptyString($cellValue);
         } else if (CellHelper::isBoolean($cellValue)) {
             $cellXML .= ' t="b"><v>' . intval($cellValue) . '</v></c>';