From 5bf565e353b73bc87e0b918368dadac701644078 Mon Sep 17 00:00:00 2001
From: Damien George <damien.p.george@gmail.com>
Date: Fri, 4 Apr 2014 00:16:32 +0100
Subject: [PATCH] py: Handle small int power overflow correctly.

---
 py/mpz.c     |  5 ++++-
 py/runtime.c | 20 ++++++++++++++++++--
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/py/mpz.c b/py/mpz.c
index 4a8941e29..21b390996 100644
--- a/py/mpz.c
+++ b/py/mpz.c
@@ -993,8 +993,11 @@ void mpz_pow_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs) {
         if (mpz_is_odd(n)) {
             mpz_mul_inpl(dest, dest, x);
         }
-        mpz_mul_inpl(x, x, x);
         n->len = mpn_shr(n->dig, n->dig, n->len, 1);
+        if (n->len == 0) {
+            break;
+        }
+        mpz_mul_inpl(x, x, x);
     }
 
     mpz_free(x);
diff --git a/py/runtime.c b/py/runtime.c
index e2e349564..d9e2298c4 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -367,18 +367,34 @@ mp_obj_t mp_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
                         nlr_jump(mp_obj_new_exception_msg(&mp_type_ValueError, "negative power with no float support"));
                         #endif
                     } else {
-                        // TODO check for overflow
                         machine_int_t ans = 1;
                         while (rhs_val > 0) {
                             if (rhs_val & 1) {
+                                machine_int_t old = ans;
                                 ans *= lhs_val;
+                                if (ans < old) {
+                                    goto power_overflow;
+                                }
+                            }
+                            if (rhs_val == 1) {
+                                break;
                             }
-                            lhs_val *= lhs_val;
                             rhs_val /= 2;
+                            machine_int_t old = lhs_val;
+                            lhs_val *= lhs_val;
+                            if (lhs_val < old) {
+                                goto power_overflow;
+                            }
                         }
                         lhs_val = ans;
                     }
                     break;
+
+                power_overflow:
+                    // use higher precision
+                    lhs = mp_obj_new_int_from_ll(MP_OBJ_SMALL_INT_VALUE(lhs));
+                    goto generic_binary_op;
+
                 case MP_BINARY_OP_LESS: return MP_BOOL(lhs_val < rhs_val); break;
                 case MP_BINARY_OP_MORE: return MP_BOOL(lhs_val > rhs_val); break;
                 case MP_BINARY_OP_LESS_EQUAL: return MP_BOOL(lhs_val <= rhs_val); break;