Issue #25221: merge from 3.5.

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.6.0 beta 1
 Core and Builtins
 -----------------
 
+- Issue #25221: Fix corrupted result from PyLong_FromLong(0) when Python
+  is compiled with NSMALLPOSINTS = 0.
+
 - Issue #27080: Implement formatting support for PEP 515.  Initial patch
   by Chris Angelico.
 

Objects/longobject.c

@@ -234,7 +234,7 @@ PyLong_FromLong(long ival)
     unsigned long abs_ival;
     unsigned long t;  /* unsigned so >> doesn't propagate sign bit */
     int ndigits = 0;
-    int sign = 1;
+    int sign;
 
     CHECK_SMALL_INT(ival);
 
@@ -246,6 +246,7 @@ PyLong_FromLong(long ival)
     }
     else {
         abs_ival = (unsigned long)ival;
+        sign = ival == 0 ? 0 : 1;
     }
 
     /* Fast path for single-digit ints */