Fix: Exponentiation of integer constants

Cython/Compiler/ExprNodes.py

@@ -11745,6 +11745,12 @@ class PowNode(NumBinopNode):
             error(self.pos, "got unexpected types for C power operator: %s, %s" %
                             (self.operand1.type, self.operand2.type))
 
+    def compute_c_result_type(self, type1, type2):
+        c_result_type = super(PowNode, self).compute_c_result_type(type1, type2)
+        if isinstance(self.operand2.constant_result, _py_int_types) and self.operand2.constant_result < 0:
+            c_result_type = PyrexTypes.widest_numeric_type(c_result_type, PyrexTypes.c_double_type)
+        return c_result_type
+
     def calculate_result_code(self):
         # Work around MSVC overloading ambiguity.
         def typecast(operand):

tests/run/constant_folding.py

@@ -136,6 +136,17 @@ def binop_mul_pow():
     return (mul_int, mul_large_int, pow_int, pow_large_int)
 
 
+def binop_pow_negative():
+    """
+    >>> print_big_ints(binop_pow_negative())
+    (4.018775720164609e-06, 8.020807320287816e-38, 0.1)
+    """
+    pow_int = 12 ** -5
+    pow_large_int = 1234 ** -12
+    pow_expression_int = 10 ** (1-2)
+    return (pow_int, pow_large_int, pow_expression_int)
+
+
 @cython.test_fail_if_path_exists(
     "//SliceIndexNode",
 )