From 66f21389a74223b6a6372919f5c060faecad0fd8 Mon Sep 17 00:00:00 2001
From: Jakob Kummerow <jkummerow@chromium.org>
Date: Mon, 5 Mar 2018 19:02:21 -0800
Subject: [PATCH] [bigint] Fix Exponentiate for 1 ** multi_digit

Bug: chromium:819026
Change-Id: I2c58d5e2892f683747966e00aa047153085ac121
Reviewed-on: https://chromium-review.googlesource.com/950472
Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51776}
---
 src/objects/bigint.cc              | 10 +++++++++-
 test/mjsunit/harmony/bigint/exp.js |  3 +++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/objects/bigint.cc b/src/objects/bigint.cc
index db00ab1bf1ff..ee21d52a5600 100644
--- a/src/objects/bigint.cc
+++ b/src/objects/bigint.cc
@@ -323,10 +323,18 @@ MaybeHandle<BigInt> BigInt::Exponentiate(Handle<BigInt> base,
   // 3. Return a BigInt representing the mathematical value of base raised
   //    to the power exponent.
   if (base->is_zero()) return base;
+  if (base->length() == 1 && base->digit(0) == 1) {
+    // (-1) ** even_number == 1.
+    if (base->sign() && (exponent->digit(0) & 1) == 0) {
+      return UnaryMinus(base);
+    }
+    // (-1) ** odd_number == -1; 1 ** anything == 1.
+    return base;
+  }
   // For all bases >= 2, very large exponents would lead to unrepresentable
   // results.
   STATIC_ASSERT(kMaxLengthBits < std::numeric_limits<digit_t>::max());
-  if (!(base->length() == 1 && base->digit(0) == 1) && exponent->length() > 1) {
+  if (exponent->length() > 1) {
     THROW_NEW_ERROR(isolate, NewRangeError(MessageTemplate::kBigIntTooBig),
                     BigInt);
   }
diff --git a/test/mjsunit/harmony/bigint/exp.js b/test/mjsunit/harmony/bigint/exp.js
index 812173323982..54d5849373f5 100644
--- a/test/mjsunit/harmony/bigint/exp.js
+++ b/test/mjsunit/harmony/bigint/exp.js
@@ -9,6 +9,9 @@ assertEquals(-1n, (-1n) ** 1n);
 assertEquals(1n, (-1n) ** 2n);
 assertEquals(-1n, (-1n) ** 3n);
 assertEquals(1n, (-1n) ** 4n);
+// Multi-digit exponents.
+assertEquals(1n, (-1n) ** (2n ** 80n));
+assertEquals(-1n, (-1n) ** ((2n ** 80n) + 1n));
 
 assertEquals(1n, 0n ** 0n);
 assertEquals(0n, 0n ** 1n);