intern ints from -5 to 256 like cpython does

this increases the compatibility if some one is using 'is' identity comparisons
instead of equality '==' comparisons.

src/runtime/int.cpp

@@ -1359,9 +1359,9 @@ void setupInt() {
     static PyNumberMethods int_as_number;
     int_cls->tp_as_number = &int_as_number;
 
-    for (int i = 0; i < NUM_INTERNED_INTS; i++) {
-        interned_ints[i] = new BoxedInt(i);
-        gc::registerPermanentRoot(interned_ints[i]);
+    for (int i = MIN_INTERNED_INT; i <= MAX_INTERNED_INT; i++) {
+        interned_ints[-MIN_INTERNED_INT + i] = new BoxedInt(i);
+        gc::registerPermanentRoot(interned_ints[-MIN_INTERNED_INT + i]);
     }
 
     int_cls->giveAttr("__getnewargs__", new BoxedFunction(FunctionMetadata::create((void*)int_getnewargs, UNKNOWN, 1,

src/runtime/types.h

@@ -1163,11 +1163,15 @@ inline BoxedString* boxString(llvm::StringRef s) {
     return new (s.size()) BoxedString(s);
 }
 
-#define NUM_INTERNED_INTS 100
+#define MIN_INTERNED_INT -5  // inclusive
+#define MAX_INTERNED_INT 256 // inclusive
+static_assert(MIN_INTERNED_INT < 0 && MAX_INTERNED_INT > 0, "");
+#define NUM_INTERNED_INTS ((-MIN_INTERNED_INT) + MAX_INTERNED_INT + 1)
+
 extern BoxedInt* interned_ints[NUM_INTERNED_INTS];
 extern "C" inline Box* boxInt(int64_t n) {
-    if (0 <= n && n < NUM_INTERNED_INTS) {
-        return interned_ints[n];
+    if (n >= MIN_INTERNED_INT && n <= MAX_INTERNED_INT) {
+        return interned_ints[(-MIN_INTERNED_INT) + n];
     }
     return new BoxedInt(n);
 }