REF: replace deprecated headers

double-conversion/bignum-dtoa.cc

diff --git a/double-conversion/bignum-dtoa.cc b/double-conversion/bignum-dtoa.cc
index bdb06a2..526f96e 100644
--- a/double-conversion/bignum-dtoa.cc
+++ b/double-conversion/bignum-dtoa.cc
@@ -25,7 +25,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include <math.h>
+#include <cmath>
 
 #include <double-conversion/bignum-dtoa.h>
 

double-conversion/cached-powers.cc

diff --git a/double-conversion/cached-powers.cc b/double-conversion/cached-powers.cc
index 780f527..6f771e9 100644
--- a/double-conversion/cached-powers.cc
+++ b/double-conversion/cached-powers.cc
@@ -25,9 +25,9 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include <stdarg.h>
-#include <limits.h>
-#include <math.h>
+#include <climits>
+#include <cmath>
+#include <cstdarg>
 
 #include <double-conversion/utils.h>
 

double-conversion/double-conversion.cc

diff --git a/double-conversion/double-conversion.cc b/double-conversion/double-conversion.cc
index 7bd7df0..a65fd4d 100644
--- a/double-conversion/double-conversion.cc
+++ b/double-conversion/double-conversion.cc
@@ -25,9 +25,9 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include <limits.h>
+#include <climits>
 #include <locale>
-#include <math.h>
+#include <cmath>
 
 #include <double-conversion/double-conversion.h>
 

double-conversion/fixed-dtoa.cc

diff --git a/double-conversion/fixed-dtoa.cc b/double-conversion/fixed-dtoa.cc
index 5b6ca5a..8c111ac 100644
--- a/double-conversion/fixed-dtoa.cc
+++ b/double-conversion/fixed-dtoa.cc
@@ -25,7 +25,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include <math.h>
+#include <cmath>
 
 #include <double-conversion/fixed-dtoa.h>
 #include <double-conversion/ieee.h>

double-conversion/strtod.cc

diff --git a/double-conversion/strtod.cc b/double-conversion/strtod.cc
index 50eacf0..3a59b69 100644
--- a/double-conversion/strtod.cc
+++ b/double-conversion/strtod.cc
@@ -25,13 +25,13 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include <stdarg.h>
-#include <limits.h>
+#include <climits>
+#include <cstdarg>
 
-#include <double-conversion/strtod.h>
 #include <double-conversion/bignum.h>
 #include <double-conversion/cached-powers.h>
 #include <double-conversion/ieee.h>
+#include <double-conversion/strtod.h>
 
 namespace double_conversion {
 

double-conversion/utils.h

diff --git a/double-conversion/utils.h b/double-conversion/utils.h
index 2c745f3..04af875 100644
--- a/double-conversion/utils.h
+++ b/double-conversion/utils.h
@@ -28,10 +28,10 @@
 #ifndef DOUBLE_CONVERSION_UTILS_H_
 #define DOUBLE_CONVERSION_UTILS_H_
 
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
-#include <assert.h>
+#include <cassert>
 #ifndef ASSERT
 #define ASSERT(condition)         \
     assert(condition);