Fix for floating point durations

The duration calculation was using %, but that's only supported on
duration objects when the arithmetic type supports %, and hence fails
for floats.  Fixed by subtracting off the calculated values instead.

include/pybind11/chrono.h

@@ -85,9 +85,11 @@ public:
         using ss_t = duration<int, std::ratio<1>>;
         using ss_t = duration<int, std::ratio<1>>;
         using us_t = duration<int, std::micro>;
         using us_t = duration<int, std::micro>;
 
 
-        return PyDelta_FromDSU(duration_cast<dd_t>(d).count(),
-                               duration_cast<ss_t>(d % days(1)).count(),
-                               duration_cast<us_t>(d % seconds(1)).count());
+        auto dd = duration_cast<dd_t>(d);
+        auto subd = d - dd;
+        auto ss = duration_cast<ss_t>(subd);
+        auto us = duration_cast<us_t>(subd - ss);
+        return PyDelta_FromDSU(dd.count(), ss.count(), us.count());
     }
     }
 
 
     PYBIND11_TYPE_CASTER(type, _("datetime.timedelta"));
     PYBIND11_TYPE_CASTER(type, _("datetime.timedelta"));

tests/test_chrono.cpp

@@ -48,6 +48,11 @@ std::chrono::microseconds test_chrono7(std::chrono::microseconds t) {
     return t;
     return t;
 }
 }
 
 
+// Float durations (issue #719)
+std::chrono::duration<double> test_chrono_float_diff(std::chrono::duration<float> a, std::chrono::duration<float> b) {
+    return a - b;
+}
+
 test_initializer chrono([] (py::module &m) {
 test_initializer chrono([] (py::module &m) {
     m.def("test_chrono1", &test_chrono1);
     m.def("test_chrono1", &test_chrono1);
     m.def("test_chrono2", &test_chrono2);
     m.def("test_chrono2", &test_chrono2);
@@ -56,4 +61,5 @@ test_initializer chrono([] (py::module &m) {
     m.def("test_chrono5", &test_chrono5);
     m.def("test_chrono5", &test_chrono5);
     m.def("test_chrono6", &test_chrono6);
     m.def("test_chrono6", &test_chrono6);
     m.def("test_chrono7", &test_chrono7);
     m.def("test_chrono7", &test_chrono7);
+    m.def("test_chrono_float_diff", &test_chrono_float_diff);
 });
 });

tests/test_chrono.py

@@ -104,7 +104,7 @@ def test_chrono_steady_clock_roundtrip():
 
 
 
 
 def test_floating_point_duration():
 def test_floating_point_duration():
-    from pybind11_tests import test_chrono7
+    from pybind11_tests import test_chrono7, test_chrono_float_diff
     import datetime
     import datetime
 
 
     # Test using 35.525123 seconds as an example floating point number in seconds
     # Test using 35.525123 seconds as an example floating point number in seconds
@@ -114,3 +114,7 @@ def test_floating_point_duration():
 
 
     assert time.seconds == 35
     assert time.seconds == 35
     assert 525122 <= time.microseconds <= 525123
     assert 525122 <= time.microseconds <= 525123
+
+    diff = test_chrono_float_diff(43.789012, 1.123456)
+    assert diff.seconds == 42
+    assert 665556 <= diff.microseconds <= 665557