Fix use of negative numbers in math equations. (#903)

Fixes #895

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - Registered output filters wouldn't run [#899](https://github.com/smarty-php/smarty/issues/899)
+- Use of negative numbers in {math} equations [#895](https://github.com/smarty-php/smarty/issues/895)
 
 ### Removed
 - Removed `$smarty->registered_filters` array

src/FunctionHandler/Math.php

@@ -66,7 +66,7 @@ class Math extends Base {
 		$equation = preg_replace('/\s+/', '', $equation);
 
 		// Adapted from https://www.php.net/manual/en/function.eval.php#107377
-		$number = '(?:\d+(?:[,.]\d+)?|pi|π)'; // What is a number
+		$number = '-?(?:\d+(?:[,.]\d+)?|pi|π)'; // What is a number
 		$functionsOrVars = '((?:0x[a-fA-F0-9]+)|([a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*))';
 		$operators = '[,+\/*\^%-]'; // Allowed math operators
 		$regexp = '/^((' . $number . '|' . $functionsOrVars . '|(' . $functionsOrVars . '\s*\((?1)*\)|\((?1)*\)))(?:' . $operators . '(?1))?)+$/';

tests/UnitTests/TemplateSource/ValueTests/Math/MathTest.php

@@ -93,6 +93,14 @@ class MathTest extends PHPUnit_Smarty
         $this->assertEquals($expected, $this->smarty->fetch($tpl));
     }
 
+    public function testNegativeNumbers()
+    {
+        $this->smarty->disableSecurity();
+        $expected = "-19 -- 4.1";
+        $tpl = $this->smarty->createTemplate('eval:{$x = 4}{$y = 5.5}{math equation="-2.0*(x+y)" x=$x y=$y} -- {math equation="-20.5 / -5"}');
+        $this->assertEquals($expected, $this->smarty->fetch($tpl));
+    }
+
     public function testSyntaxFormat()
     {
         $this->smarty->disableSecurity();