1 files changed, 66 insertions, 0 deletions
diff --git a/src/Core.php b/src/Core.php
new file mode 100644
index 0000000..b68dd2f
--- /dev/null
+++ b/src/Core.php
@@ -0,0 +1,66 @@
+<?php
+namespace ParagonIE\ConstantTime;
+
+abstract class Core
+{
+    /**
+     * Safe string length
+     *
+     * @ref mbstring.func_overload
+     *
+     * @param string $str
+     * @return int
+     */
+    public static function safeStrlen($str)
+    {
+        if (\function_exists('mb_strlen')) {
+            return \mb_strlen($str, '8bit');
+        } else {
+            return \strlen($str);
+        }
+    }
+
+    /**
+     * Safe substring
+     *
+     * @ref mbstring.func_overload
+     *
+     * @staticvar boolean $exists
+     * @param string $str
+     * @param int $start
+     * @param int $length
+     * @return string
+     * @throws \TypeError
+     */
+    public static function safeSubstr(
+        $str,
+        $start = 0,
+        $length = null
+    ) {
+        if (\function_exists('mb_substr')) {
+            // mb_substr($str, 0, NULL, '8bit') returns an empty string on PHP
+            // 5.3, so we have to find the length ourselves.
+            if ($length === null) {
+                if ($start >= 0) {
+                    $length = self::safeStrlen($str) - $start;
+                } else {
+                    $length = -$start;
+                }
+            }
+            // $length calculation above might result in a 0-length string
+            if ($length === 0) {
+                return '';
+            }
+            return \mb_substr($str, $start, $length, '8bit');
+        }
+        if ($length === 0) {
+            return '';
+        }
+        // Unlike mb_substr(), substr() doesn't accept NULL for length
+        if ($length !== null) {
+            return \substr($str, $start, $length);
+        } else {
+            return \substr($str, $start);
+        }
+    }
+}
+\ No newline at end of file