Fix bug with int64 support for FileStorage

modules/core/test/test_io.cpp

@@ -2022,6 +2022,64 @@ TEST(Core_InputOutput, FileStorage_invalid_attribute_value_regression_25946)
     ASSERT_EQ(0, std::remove(fileName.c_str()));
 }
 
+// see https://github.com/opencv/opencv/issues/26829
+TEST(Core_InputOutput, FileStorage_int64_26829)
+{
+    String content =
+        "%YAML:1.0\n"
+        "String1: string1\n"
+        "IntMin: -2147483648\n"
+        "String2: string2\n"
+        "Int64Min: -9223372036854775808\n"
+        "String3: string3\n"
+        "IntMax: 2147483647\n"
+        "String4: string4\n"
+        "Int64Max: 9223372036854775807\n"
+        "String5: string5\n";
+
+    FileStorage fs(content, FileStorage::READ | FileStorage::MEMORY);
+
+    {
+        std::string str;
+
+        fs["String1"] >> str;
+        EXPECT_EQ(str, "string1");
+
+        fs["String2"] >> str;
+        EXPECT_EQ(str, "string2");
+
+        fs["String3"] >> str;
+        EXPECT_EQ(str, "string3");
+
+        fs["String4"] >> str;
+        EXPECT_EQ(str, "string4");
+
+        fs["String5"] >> str;
+        EXPECT_EQ(str, "string5");
+    }
+
+    {
+        int value;
+
+        fs["IntMin"] >> value;
+        EXPECT_EQ(value, INT_MIN);
+
+        fs["IntMax"] >> value;
+        EXPECT_EQ(value, INT_MAX);
+    }
+
+
+    {
+        int64_t value;
+
+        fs["Int64Min"] >> value;
+        EXPECT_EQ(value, INT64_MIN);
+
+        fs["Int64Max"] >> value;
+        EXPECT_EQ(value, INT64_MAX);
+    }
+}
+
 template <typename T>
 T fsWriteRead(const T& expectedValue, const char* ext)
 {