undo change to lower bound

pandas/lib.pyx

@@ -65,13 +65,8 @@ cdef int64_t NPY_NAT = util.get_nat()
 ctypedef unsigned char UChar
 
 cimport util
-from util cimport is_array, _checknull, _checknan
-
-cdef extern from "headers/stdint.h":
-    enum: UINT8_MAX
-    enum: INT64_MAX
-    enum: INT64_MIN
-
+from util cimport (is_array, _checknull, _checknan, INT64_MAX,
+                   INT64_MIN, UINT8_MAX)
 
 cdef extern from "math.h":
     double sqrt(double x)

pandas/src/inference.pyx

@@ -6,19 +6,9 @@ iNaT = util.get_nat()
 
 cdef bint PY2 = sys.version_info[0] == 2
 
-cdef extern from "headers/stdint.h":
-    enum: UINT8_MAX
-    enum: UINT16_MAX
-    enum: UINT32_MAX
-    enum: UINT64_MAX
-    enum: INT8_MIN
-    enum: INT8_MAX
-    enum: INT16_MIN
-    enum: INT16_MAX
-    enum: INT32_MAX
-    enum: INT32_MIN
-    enum: INT64_MAX
-    enum: INT64_MIN
+from util cimport (UINT8_MAX, UINT16_MAX, UINT32_MAX, UINT64_MAX,
+                   INT8_MIN, INT8_MAX, INT16_MIN, INT16_MAX,
+                   INT32_MAX, INT32_MIN, INT64_MAX, INT64_MIN)
 
 # core.common import for fast inference checks
 

pandas/src/util.pxd

@@ -38,6 +38,20 @@ ctypedef fused numeric:
     cnp.float32_t
     cnp.float64_t
 
+cdef extern from "headers/stdint.h":
+    enum: UINT8_MAX
+    enum: UINT16_MAX
+    enum: UINT32_MAX
+    enum: UINT64_MAX
+    enum: INT8_MIN
+    enum: INT8_MAX
+    enum: INT16_MIN
+    enum: INT16_MAX
+    enum: INT32_MAX
+    enum: INT32_MIN
+    enum: INT64_MAX
+    enum: INT64_MIN
+
 cdef inline object get_value_at(ndarray arr, object loc):
     cdef:
         Py_ssize_t i, sz

pandas/tslib.pyx

@@ -25,10 +25,6 @@ from cpython cimport (
 )
 
 
-cdef extern from "headers/stdint.h":
-    enum: INT64_MAX
-    enum: INT64_MIN
-
 # Cython < 0.17 doesn't have this in cpython
 cdef extern from "Python.h":
     cdef PyTypeObject *Py_TYPE(object)
@@ -42,7 +38,7 @@ from datetime cimport cmp_pandas_datetimestruct
 from libc.stdlib cimport free
 
 from util cimport (is_integer_object, is_float_object, is_datetime64_object,
-                   is_timedelta64_object)
+                   is_timedelta64_object, INT64_MAX)
 cimport util
 
 from datetime cimport *
@@ -909,9 +905,12 @@ cpdef object get_value_box(ndarray arr, object loc):
 
 
 # Add the min and max fields at the class level
-# INT64_MIN is reserved for NaT
-cdef int64_t _NS_LOWER_BOUND = INT64_MIN + 1
 cdef int64_t _NS_UPPER_BOUND = INT64_MAX
+# smallest value we could actually represent is
+#   INT64_MIN + 1 == -9223372036854775807
+# but to allow overflow free conversion with a microsecond resolution
+# use the smallest value with a 0 nanosecond unit
+cdef int64_t _NS_LOWER_BOUND = -9223285636854775000LL
 
 cdef pandas_datetimestruct _NS_MIN_DTS, _NS_MAX_DTS
 pandas_datetime_to_datetimestruct(_NS_LOWER_BOUND, PANDAS_FR_ns, &_NS_MIN_DTS)