Test (and fix) corner case in C division

Cython/Compiler/ExprNodes.py

@@ -5717,7 +5717,7 @@ static INLINE %(type)s __Pyx_mod_%(type_name)s(%(type)s, %(type)s); /* proto */
 impl="""
 static INLINE %(type)s __Pyx_mod_%(type_name)s(%(type)s a, %(type)s b) {
     %(type)s res = fmod%(math_h_modifier)s(a, b);
-    res += ((res < 0) ^ (b < 0)) * b;
+    res += ((res != 0) & ((a < 0) ^ (b < 0))) * b;
     return res;
 }
 """)
@@ -5728,9 +5728,9 @@ static INLINE %(type)s __Pyx_div_%(type_name)s(%(type)s, %(type)s); /* proto */
 """,
 impl="""
 static INLINE %(type)s __Pyx_div_%(type_name)s(%(type)s a, %(type)s b) {
-    %(type)s res = a / b;
-    res -= (res < 0);
-    return res;
+    %(type)s q = a / b;
+    q -= ((q*b != a) & ((a < 0) ^ (b < 0)));
+    return q;
 }
 """)
 

tests/run/cdivision_CEP_516.pyx

@@ -27,6 +27,10 @@ True
 >>> [test_cdiv_cmod(a, b) for a, b in v]
 [(1, 7), (-1, -7), (1, -7), (-1, 7)]
 
+>>> all([mod_int_py(a,b) == a % b for a in range(-10, 10) for b in range(-10, 10) if b != 0])
+True
+>>> all([div_int_py(a,b) == a // b for a in range(-10, 10) for b in range(-10, 10) if b != 0])
+True
 
 >>> def simple_warn(msg, *args): print msg
 >>> import warnings