PHP 8.5: Refactor exponent handling in BigNumber to prevent warning

Author: julien-boudry

src/BigNumber.php

@@ -15,13 +15,17 @@
 
 use function array_shift;
 use function assert;
+use function filter_var;
 use function is_float;
 use function is_int;
 use function ltrim;
 use function preg_match;
 use function str_contains;
 use function str_repeat;
 use function strlen;
+use function substr;
+
+use const FILTER_VALIDATE_INT;
 
 use const PHP_INT_MAX;
 use const PHP_INT_MIN;
@@ -503,9 +507,23 @@ private static function _of(BigNumber|int|float|string $value): BigNumber
 
             if ($point !== null || $exponent !== null) {
                 $fractional ??= '';
-                $exponent = ($exponent !== null) ? (int) $exponent : 0;
 
-                if ($exponent === PHP_INT_MIN || $exponent === PHP_INT_MAX) {
+                if ($exponent !== null) {
+                    if (substr($exponent, 0, 1) === '-') {
+                        $exponent = ltrim(substr($exponent, 1), '0') ?: '0';
+                        $exponent = filter_var($exponent, FILTER_VALIDATE_INT);
+                        if ($exponent !== false) {
+                            $exponent = -$exponent;
+                        }
+                    } else {
+                        $exponent = ltrim($exponent, '+0') ?: '0';
+                        $exponent = filter_var($exponent, FILTER_VALIDATE_INT);
+                    }
+                } else {
+                    $exponent = 0;
+                }
+
+                if ($exponent === false || $exponent === PHP_INT_MIN || $exponent === PHP_INT_MAX) {
                     throw new NumberFormatException('Exponent too large.');
                 }