Merge pull request #4641 from oleibman/issue4638

Proper Output for BASE Function

Author: oleibman

CHANGELOG.md

@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org). Thia is a
 - Minor improvements to Calculation coverage. [PR #4624](https://github.com/PHPOffice/PhpSpreadsheet/pull/4624)
 - Conditional formatting in extLst. [Issue #4629](https://github.com/PHPOffice/PhpSpreadsheet/issues/4629) [PR #4633](https://github.com/PHPOffice/PhpSpreadsheet/pull/4633)
 - Php8.5 deprecates use of null as array index. [PR #4634](https://github.com/PHPOffice/PhpSpreadsheet/pull/4634)
+- Use prefix _xlfn for BASE function. [Issue #4638](https://github.com/PHPOffice/PhpSpreadsheet/issues/4638) [PR #4641](https://github.com/PHPOffice/PhpSpreadsheet/pull/4641)
 
 ## 2025-09-03 - 5.1.0
 

src/PhpSpreadsheet/Writer/Xlsx/FunctionPrefix.php

@@ -66,6 +66,8 @@ class FunctionPrefix
         . '|var[.]s'
         . '|weibull[.]dist'
         . '|z[.]test'
+        // probably added with Excel 2010 but not properly documented
+        . '|base'
         // functions added with Excel 2013
         . '|acot'
         . '|acoth'

tests/PhpSpreadsheetTests/Writer/Xlsx/FunctionPrefixTest.php

@@ -38,6 +38,7 @@ public static function functionPrefixProvider(): array
             'DAYS/NETWORKDAYS 5' => ['NETWORKDAYS(DATE(2023,1,1),TODAY(), C:C)', 'NETWORKDAYS(DATE(2023,1,1),TODAY(), C:C)'],
             'COUNTIFS reclassified as Legacy' => ['COUNTIFS()', 'COUNTIFS()'],
             'SUMIFS reclassified as Legacy' => ['SUMIFS()', 'SUMIFS()'],
+            'BASE improperly classified by MS' => ['_xlfn.BASE()', 'BASE()'],
         ];
     }
 }