[bigint] Move bitwise ops to src/bigint/

No asymptotic improvements, and none are planned either.
Minor speedups (25-50%) through reduced overhead: accessing Digits
is faster than working with Handle<BigInt>, and this implementation
avoids allocating intermediate results.

Bug: v8:11515
Change-Id: I2aab2b1c5c9cbb910800161b8514c497daf2b587
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3149453
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76793}

BUILD.bazel

@@ -2727,6 +2727,7 @@ filegroup(
         "src/bigint/bigint-internal.cc",
         "src/bigint/bigint-internal.h",
         "src/bigint/bigint.h",
+        "src/bigint/bitwise.cc",
         "src/bigint/digit-arithmetic.h",
         "src/bigint/div-barrett.cc",
         "src/bigint/div-burnikel.cc",

BUILD.gn

@@ -5106,6 +5106,7 @@ v8_source_set("v8_bigint") {
     "src/bigint/bigint-internal.cc",
     "src/bigint/bigint-internal.h",
     "src/bigint/bigint.h",
+    "src/bigint/bitwise.cc",
     "src/bigint/digit-arithmetic.h",
     "src/bigint/div-burnikel.cc",
     "src/bigint/div-helpers.cc",

src/bigint/bigint.h

@@ -227,12 +227,32 @@ void Add(RWDigits Z, Digits X, Digits Y);
 // Addition of signed integers. Returns true if the result is negative.
 bool AddSigned(RWDigits Z, Digits X, bool x_negative, Digits Y,
                bool y_negative);
+// Z := X + 1
+void AddOne(RWDigits Z, Digits X);
 
 // Z := X - Y. Requires X >= Y.
 void Subtract(RWDigits Z, Digits X, Digits Y);
 // Subtraction of signed integers. Returns true if the result is negative.
 bool SubtractSigned(RWDigits Z, Digits X, bool x_negative, Digits Y,
                     bool y_negative);
+// Z := X - 1
+void SubtractOne(RWDigits Z, Digits X);
+
+// The bitwise operations assume that negative BigInts are represented as
+// sign+magnitude. Their behavior depends on the sign of the inputs: negative
+// inputs perform an implicit conversion to two's complement representation.
+// Z := X & Y
+void BitwiseAnd_PosPos(RWDigits Z, Digits X, Digits Y);
+// Call this for a BigInt x = (magnitude=X, negative=true).
+void BitwiseAnd_NegNeg(RWDigits Z, Digits X, Digits Y);
+// Positive X, negative Y. Callers must swap arguments as needed.
+void BitwiseAnd_PosNeg(RWDigits Z, Digits X, Digits Y);
+void BitwiseOr_PosPos(RWDigits Z, Digits X, Digits Y);
+void BitwiseOr_NegNeg(RWDigits Z, Digits X, Digits Y);
+void BitwiseOr_PosNeg(RWDigits Z, Digits X, Digits Y);
+void BitwiseXor_PosPos(RWDigits Z, Digits X, Digits Y);
+void BitwiseXor_NegNeg(RWDigits Z, Digits X, Digits Y);
+void BitwiseXor_PosNeg(RWDigits Z, Digits X, Digits Y);
 
 enum class Status { kOk, kInterrupted };
 
@@ -303,6 +323,28 @@ int ToStringResultLength(Digits X, int radix, bool sign);
 // In DEBUG builds, the result of {ToString} will be initialized to this value.
 constexpr char kStringZapValue = '?';
 
+inline int BitwiseAnd_PosPos_ResultLength(int x_length, int y_length) {
+  return std::min(x_length, y_length);
+}
+inline int BitwiseAnd_NegNeg_ResultLength(int x_length, int y_length) {
+  // Result length growth example: -2 & -3 = -4 (2-bit inputs, 3-bit result).
+  return std::max(x_length, y_length) + 1;
+}
+inline int BitwiseAnd_PosNeg_ResultLength(int x_length) { return x_length; }
+inline int BitwiseOrResultLength(int x_length, int y_length) {
+  return std::max(x_length, y_length);
+}
+inline int BitwiseXor_PosPos_ResultLength(int x_length, int y_length) {
+  return std::max(x_length, y_length);
+}
+inline int BitwiseXor_NegNeg_ResultLength(int x_length, int y_length) {
+  return std::max(x_length, y_length);
+}
+inline int BitwiseXor_PosNeg_ResultLength(int x_length, int y_length) {
+  // Result length growth example: 3 ^ -1 == -4 (2-bit inputs, 3-bit result).
+  return std::max(x_length, y_length) + 1;
+}
+
 // Support for parsing BigInts from Strings, using an Accumulator object
 // for intermediate state.
 

src/bigint/bitwise.cc

@@ -0,0 +1,136 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/bigint/bigint-internal.h"
+#include "src/bigint/digit-arithmetic.h"
+#include "src/bigint/vector-arithmetic.h"
+
+namespace v8 {
+namespace bigint {
+
+void BitwiseAnd_PosPos(RWDigits Z, Digits X, Digits Y) {
+  int pairs = std::min(X.len(), Y.len());
+  DCHECK(Z.len() >= pairs);
+  int i = 0;
+  for (; i < pairs; i++) Z[i] = X[i] & Y[i];
+  for (; i < Z.len(); i++) Z[i] = 0;
+}
+
+void BitwiseAnd_NegNeg(RWDigits Z, Digits X, Digits Y) {
+  // (-x) & (-y) == ~(x-1) & ~(y-1)
+  //             == ~((x-1) | (y-1))
+  //             == -(((x-1) | (y-1)) + 1)
+  int pairs = std::min(X.len(), Y.len());
+  digit_t x_borrow = 1;
+  digit_t y_borrow = 1;
+  int i = 0;
+  for (; i < pairs; i++) {
+    Z[i] = digit_sub(X[i], x_borrow, &x_borrow) |
+           digit_sub(Y[i], y_borrow, &y_borrow);
+  }
+  // (At least) one of the next two loops will perform zero iterations:
+  for (; i < X.len(); i++) Z[i] = digit_sub(X[i], x_borrow, &x_borrow);
+  for (; i < Y.len(); i++) Z[i] = digit_sub(Y[i], y_borrow, &y_borrow);
+  DCHECK(x_borrow == 0);  // NOLINT(readability/check)
+  DCHECK(y_borrow == 0);  // NOLINT(readability/check)
+  for (; i < Z.len(); i++) Z[i] = 0;
+  Add(Z, 1);
+}
+
+void BitwiseAnd_PosNeg(RWDigits Z, Digits X, Digits Y) {
+  // x & (-y) == x & ~(y-1)
+  int pairs = std::min(X.len(), Y.len());
+  digit_t borrow = 1;
+  int i = 0;
+  for (; i < pairs; i++) Z[i] = X[i] & ~digit_sub(Y[i], borrow, &borrow);
+  for (; i < X.len(); i++) Z[i] = X[i];
+  for (; i < Z.len(); i++) Z[i] = 0;
+}
+
+void BitwiseOr_PosPos(RWDigits Z, Digits X, Digits Y) {
+  int pairs = std::min(X.len(), Y.len());
+  int i = 0;
+  for (; i < pairs; i++) Z[i] = X[i] | Y[i];
+  // (At least) one of the next two loops will perform zero iterations:
+  for (; i < X.len(); i++) Z[i] = X[i];
+  for (; i < Y.len(); i++) Z[i] = Y[i];
+  for (; i < Z.len(); i++) Z[i] = 0;
+}
+
+void BitwiseOr_NegNeg(RWDigits Z, Digits X, Digits Y) {
+  // (-x) | (-y) == ~(x-1) | ~(y-1)
+  //             == ~((x-1) & (y-1))
+  //             == -(((x-1) & (y-1)) + 1)
+  int pairs = std::min(X.len(), Y.len());
+  digit_t x_borrow = 1;
+  digit_t y_borrow = 1;
+  int i = 0;
+  for (; i < pairs; i++) {
+    Z[i] = digit_sub(X[i], x_borrow, &x_borrow) &
+           digit_sub(Y[i], y_borrow, &y_borrow);
+  }
+  // Any leftover borrows don't matter, the '&' would drop them anyway.
+  for (; i < Z.len(); i++) Z[i] = 0;
+  Add(Z, 1);
+}
+
+void BitwiseOr_PosNeg(RWDigits Z, Digits X, Digits Y) {
+  // x | (-y) == x | ~(y-1) == ~((y-1) &~ x) == -(((y-1) &~ x) + 1)
+  int pairs = std::min(X.len(), Y.len());
+  digit_t borrow = 1;
+  int i = 0;
+  for (; i < pairs; i++) Z[i] = digit_sub(Y[i], borrow, &borrow) & ~X[i];
+  for (; i < Y.len(); i++) Z[i] = digit_sub(Y[i], borrow, &borrow);
+  DCHECK(borrow == 0);  // NOLINT(readability/check)
+  for (; i < Z.len(); i++) Z[i] = 0;
+  Add(Z, 1);
+}
+
+void BitwiseXor_PosPos(RWDigits Z, Digits X, Digits Y) {
+  int pairs = X.len();
+  if (Y.len() < X.len()) {
+    std::swap(X, Y);
+    pairs = X.len();
+  }
+  DCHECK(X.len() <= Y.len());
+  int i = 0;
+  for (; i < pairs; i++) Z[i] = X[i] ^ Y[i];
+  for (; i < Y.len(); i++) Z[i] = Y[i];
+  for (; i < Z.len(); i++) Z[i] = 0;
+}
+
+void BitwiseXor_NegNeg(RWDigits Z, Digits X, Digits Y) {
+  // (-x) ^ (-y) == ~(x-1) ^ ~(y-1) == (x-1) ^ (y-1)
+  int pairs = std::min(X.len(), Y.len());
+  digit_t x_borrow = 1;
+  digit_t y_borrow = 1;
+  int i = 0;
+  for (; i < pairs; i++) {
+    Z[i] = digit_sub(X[i], x_borrow, &x_borrow) ^
+           digit_sub(Y[i], y_borrow, &y_borrow);
+  }
+  // (At least) one of the next two loops will perform zero iterations:
+  for (; i < X.len(); i++) Z[i] = digit_sub(X[i], x_borrow, &x_borrow);
+  for (; i < Y.len(); i++) Z[i] = digit_sub(Y[i], y_borrow, &y_borrow);
+  DCHECK(x_borrow == 0);  // NOLINT(readability/check)
+  DCHECK(y_borrow == 0);  // NOLINT(readability/check)
+  for (; i < Z.len(); i++) Z[i] = 0;
+}
+
+void BitwiseXor_PosNeg(RWDigits Z, Digits X, Digits Y) {
+  // x ^ (-y) == x ^ ~(y-1) == ~(x ^ (y-1)) == -((x ^ (y-1)) + 1)
+  int pairs = std::min(X.len(), Y.len());
+  digit_t borrow = 1;
+  int i = 0;
+  for (; i < pairs; i++) Z[i] = X[i] ^ digit_sub(Y[i], borrow, &borrow);
+  // (At least) one of the next two loops will perform zero iterations:
+  for (; i < X.len(); i++) Z[i] = X[i];
+  for (; i < Y.len(); i++) Z[i] = digit_sub(Y[i], borrow, &borrow);
+  DCHECK(borrow == 0);  // NOLINT(readability/check)
+  for (; i < Z.len(); i++) Z[i] = 0;
+  Add(Z, 1);
+}
+
+}  // namespace bigint
+}  // namespace v8

src/bigint/vector-arithmetic.cc

@@ -118,5 +118,22 @@ bool SubtractSigned(RWDigits Z, Digits X, bool x_negative, Digits Y,
   return !x_negative;
 }
 
+void AddOne(RWDigits Z, Digits X) {
+  digit_t carry = 1;
+  int i = 0;
+  for (; carry > 0 && i < X.len(); i++) Z[i] = digit_add2(X[i], carry, &carry);
+  if (carry > 0) Z[i++] = carry;
+  for (; i < X.len(); i++) Z[i] = X[i];
+  for (; i < Z.len(); i++) Z[i] = 0;
+}
+
+void SubtractOne(RWDigits Z, Digits X) {
+  digit_t borrow = 1;
+  int i = 0;
+  for (; borrow > 0; i++) Z[i] = digit_sub(X[i], borrow, &borrow);
+  for (; i < X.len(); i++) Z[i] = X[i];
+  for (; i < Z.len(); i++) Z[i] = 0;
+}
+
 }  // namespace bigint
 }  // namespace v8

src/objects/bigint.cc

@@ -81,16 +81,6 @@ class MutableBigInt : public FreshlyAllocatedBigInt {
   }
 
   // Internal helpers.
-  static MaybeHandle<MutableBigInt> BitwiseAnd(Isolate* isolate,
-                                               Handle<BigInt> x,
-                                               Handle<BigInt> y);
-  static MaybeHandle<MutableBigInt> BitwiseXor(Isolate* isolate,
-                                               Handle<BigInt> x,
-                                               Handle<BigInt> y);
-  static MaybeHandle<MutableBigInt> BitwiseOr(Isolate* isolate,
-                                              Handle<BigInt> x,
-                                              Handle<BigInt> y);
-
   static Handle<BigInt> TruncateToNBits(Isolate* isolate, int n,
                                         Handle<BigInt> x);
   static Handle<BigInt> TruncateAndSubFromPowerOfTwo(Isolate* isolate, int n,
@@ -102,29 +92,6 @@ class MutableBigInt : public FreshlyAllocatedBigInt {
       MutableBigInt result_storage = MutableBigInt());
   static Handle<MutableBigInt> AbsoluteSubOne(Isolate* isolate,
                                               Handle<BigIntBase> x);
-  static MaybeHandle<MutableBigInt> AbsoluteSubOne(Isolate* isolate,
-                                                   Handle<BigIntBase> x,
-                                                   int result_length);
-
-  enum ExtraDigitsHandling { kCopy, kSkip };
-  enum SymmetricOp { kSymmetric, kNotSymmetric };
-  static inline Handle<MutableBigInt> AbsoluteBitwiseOp(
-      Isolate* isolate, Handle<BigIntBase> x, Handle<BigIntBase> y,
-      MutableBigInt result_storage, ExtraDigitsHandling extra_digits,
-      SymmetricOp symmetric,
-      const std::function<digit_t(digit_t, digit_t)>& op);
-  static Handle<MutableBigInt> AbsoluteAnd(
-      Isolate* isolate, Handle<BigIntBase> x, Handle<BigIntBase> y,
-      MutableBigInt result_storage = MutableBigInt());
-  static Handle<MutableBigInt> AbsoluteAndNot(
-      Isolate* isolate, Handle<BigIntBase> x, Handle<BigIntBase> y,
-      MutableBigInt result_storage = MutableBigInt());
-  static Handle<MutableBigInt> AbsoluteOr(
-      Isolate* isolate, Handle<BigIntBase> x, Handle<BigIntBase> y,
-      MutableBigInt result_storage = MutableBigInt());
-  static Handle<MutableBigInt> AbsoluteXor(
-      Isolate* isolate, Handle<BigIntBase> x, Handle<BigIntBase> y,
-      MutableBigInt result_storage = MutableBigInt());
 
   // Specialized helpers for shift operations.
   static MaybeHandle<BigInt> LeftShiftByAbsolute(Isolate* isolate,
@@ -146,7 +113,6 @@ class MutableBigInt : public FreshlyAllocatedBigInt {
   static uint64_t GetRawBits(BigIntBase x, bool* lossless);
 
   // Digit arithmetic helpers.
-  static inline digit_t digit_add(digit_t a, digit_t b, digit_t* carry);
   static inline digit_t digit_sub(digit_t a, digit_t b, digit_t* borrow);
   static inline bool digit_ismax(digit_t x) {
     return static_cast<digit_t>(~x) == 0;
@@ -406,7 +372,7 @@ MaybeHandle<BigInt> BigInt::BitwiseNot(Isolate* isolate, Handle<BigInt> x) {
   MaybeHandle<MutableBigInt> result;
   if (x->sign()) {
     // ~(-x) == ~(~(x-1)) == x-1
-    result = MutableBigInt::AbsoluteSubOne(isolate, x, x->length());
+    result = MutableBigInt::AbsoluteSubOne(isolate, x);
   } else {
     // ~x == -x-1 == -(x+1)
     result = MutableBigInt::AbsoluteAddOne(isolate, x, true);
@@ -673,96 +639,82 @@ bool BigInt::EqualToBigInt(BigInt x, BigInt y) {
 
 MaybeHandle<BigInt> BigInt::BitwiseAnd(Isolate* isolate, Handle<BigInt> x,
                                        Handle<BigInt> y) {
-  return MutableBigInt::MakeImmutable(MutableBigInt::BitwiseAnd(isolate, x, y));
+  bool x_sign = x->sign();
-}
+  bool y_sign = y->sign();
-
+  Handle<MutableBigInt> result;
-MaybeHandle<MutableBigInt> MutableBigInt::BitwiseAnd(Isolate* isolate,
+  if (!x_sign && !y_sign) {
-                                                     Handle<BigInt> x,
+    int result_length =
-                                                     Handle<BigInt> y) {
+        bigint::BitwiseAnd_PosPos_ResultLength(x->length(), y->length());
-  if (!x->sign() && !y->sign()) {
+    result = MutableBigInt::New(isolate, result_length).ToHandleChecked();
-    return AbsoluteAnd(isolate, x, y);
+    bigint::BitwiseAnd_PosPos(GetRWDigits(result), GetDigits(x), GetDigits(y));
-  } else if (x->sign() && y->sign()) {
+    DCHECK(!result->sign());
-    int result_length = std::max(x->length(), y->length()) + 1;
+  } else if (x_sign && y_sign) {
-    // (-x) & (-y) == ~(x-1) & ~(y-1) == ~((x-1) | (y-1))
+    int result_length =
-    // == -(((x-1) | (y-1)) + 1)
+        bigint::BitwiseAnd_NegNeg_ResultLength(x->length(), y->length());
-    Handle<MutableBigInt> result;
+    if (!MutableBigInt::New(isolate, result_length).ToHandle(&result)) {
-    if (!AbsoluteSubOne(isolate, x, result_length).ToHandle(&result)) {
+      return {};
-      return MaybeHandle<MutableBigInt>();
     }
-    Handle<MutableBigInt> y_1 = AbsoluteSubOne(isolate, y);
+    bigint::BitwiseAnd_NegNeg(GetRWDigits(result), GetDigits(x), GetDigits(y));
-    result = AbsoluteOr(isolate, result, y_1, *result);
+    result->set_sign(true);
-    return AbsoluteAddOne(isolate, result, true, *result);
   } else {
-    DCHECK(x->sign() != y->sign());
+    if (x_sign) std::swap(x, y);
-    // Assume that x is the positive BigInt.
+    int result_length = bigint::BitwiseAnd_PosNeg_ResultLength(x->length());
-    if (x->sign()) std::swap(x, y);
+    result = MutableBigInt::New(isolate, result_length).ToHandleChecked();
-    // x & (-y) == x & ~(y-1) == x &~ (y-1)
+    bigint::BitwiseAnd_PosNeg(GetRWDigits(result), GetDigits(x), GetDigits(y));
-    Handle<MutableBigInt> y_1 = AbsoluteSubOne(isolate, y);
+    DCHECK(!result->sign());
-    return AbsoluteAndNot(isolate, x, y_1);
   }
+  return MutableBigInt::MakeImmutable(result);
 }
 
 MaybeHandle<BigInt> BigInt::BitwiseXor(Isolate* isolate, Handle<BigInt> x,
                                        Handle<BigInt> y) {
-  return MutableBigInt::MakeImmutable(MutableBigInt::BitwiseXor(isolate, x, y));
+  bool x_sign = x->sign();
-}
+  bool y_sign = y->sign();
-
+  Handle<MutableBigInt> result;
-MaybeHandle<MutableBigInt> MutableBigInt::BitwiseXor(Isolate* isolate,
+  if (!x_sign && !y_sign) {
-                                                     Handle<BigInt> x,
+    int result_length =
-                                                     Handle<BigInt> y) {
+        bigint::BitwiseXor_PosPos_ResultLength(x->length(), y->length());
-  if (!x->sign() && !y->sign()) {
+    result = MutableBigInt::New(isolate, result_length).ToHandleChecked();
-    return AbsoluteXor(isolate, x, y);
+    bigint::BitwiseXor_PosPos(GetRWDigits(result), GetDigits(x), GetDigits(y));
-  } else if (x->sign() && y->sign()) {
+    DCHECK(!result->sign());
-    int result_length = std::max(x->length(), y->length());
+  } else if (x_sign && y_sign) {
-    // (-x) ^ (-y) == ~(x-1) ^ ~(y-1) == (x-1) ^ (y-1)
+    int result_length =
-    Handle<MutableBigInt> result =
+        bigint::BitwiseXor_NegNeg_ResultLength(x->length(), y->length());
-        AbsoluteSubOne(isolate, x, result_length).ToHandleChecked();
+    result = MutableBigInt::New(isolate, result_length).ToHandleChecked();
-    Handle<MutableBigInt> y_1 = AbsoluteSubOne(isolate, y);
+    bigint::BitwiseXor_NegNeg(GetRWDigits(result), GetDigits(x), GetDigits(y));
-    return AbsoluteXor(isolate, result, y_1, *result);
+    DCHECK(!result->sign());
   } else {
-    DCHECK(x->sign() != y->sign());
+    if (x_sign) std::swap(x, y);
-    int result_length = std::max(x->length(), y->length()) + 1;
+    int result_length =
-    // Assume that x is the positive BigInt.
+        bigint::BitwiseXor_PosNeg_ResultLength(x->length(), y->length());
-    if (x->sign()) std::swap(x, y);
+    if (!MutableBigInt::New(isolate, result_length).ToHandle(&result)) {
-    // x ^ (-y) == x ^ ~(y-1) == ~(x ^ (y-1)) == -((x ^ (y-1)) + 1)
+      return {};
-    Handle<MutableBigInt> result;
-    if (!AbsoluteSubOne(isolate, y, result_length).ToHandle(&result)) {
-      return MaybeHandle<MutableBigInt>();
     }
-    result = AbsoluteXor(isolate, result, x, *result);
+    bigint::BitwiseXor_PosNeg(GetRWDigits(result), GetDigits(x), GetDigits(y));
-    return AbsoluteAddOne(isolate, result, true, *result);
+    result->set_sign(true);
   }
+  return MutableBigInt::MakeImmutable(result);
 }
 
 MaybeHandle<BigInt> BigInt::BitwiseOr(Isolate* isolate, Handle<BigInt> x,
                                       Handle<BigInt> y) {
-  return MutableBigInt::MakeImmutable(MutableBigInt::BitwiseOr(isolate, x, y));
+  bool x_sign = x->sign();
-}
+  bool y_sign = y->sign();
-
+  int result_length = bigint::BitwiseOrResultLength(x->length(), y->length());
-MaybeHandle<MutableBigInt> MutableBigInt::BitwiseOr(Isolate* isolate,
+  Handle<MutableBigInt> result =
-                                                    Handle<BigInt> x,
+      MutableBigInt::New(isolate, result_length).ToHandleChecked();
-                                                    Handle<BigInt> y) {
+  if (!x_sign && !y_sign) {
-  int result_length = std::max(x->length(), y->length());
+    bigint::BitwiseOr_PosPos(GetRWDigits(result), GetDigits(x), GetDigits(y));
-  if (!x->sign() && !y->sign()) {
+    DCHECK(!result->sign());
-    return AbsoluteOr(isolate, x, y);
+  } else if (x_sign && y_sign) {
-  } else if (x->sign() && y->sign()) {
+    bigint::BitwiseOr_NegNeg(GetRWDigits(result), GetDigits(x), GetDigits(y));
-    // (-x) | (-y) == ~(x-1) | ~(y-1) == ~((x-1) & (y-1))
+    result->set_sign(true);
-    // == -(((x-1) & (y-1)) + 1)
-    Handle<MutableBigInt> result =
-        AbsoluteSubOne(isolate, x, result_length).ToHandleChecked();
-    Handle<MutableBigInt> y_1 = AbsoluteSubOne(isolate, y);
-    result = AbsoluteAnd(isolate, result, y_1, *result);
-    return AbsoluteAddOne(isolate, result, true, *result);
   } else {
-    DCHECK(x->sign() != y->sign());
+    if (x_sign) std::swap(x, y);
-    // Assume that x is the positive BigInt.
+    bigint::BitwiseOr_PosNeg(GetRWDigits(result), GetDigits(x), GetDigits(y));
-    if (x->sign()) std::swap(x, y);
+    result->set_sign(true);
-    // x | (-y) == x | ~(y-1) == ~((y-1) &~ x) == -(((y-1) &~ x) + 1)
-    Handle<MutableBigInt> result =
-        AbsoluteSubOne(isolate, y, result_length).ToHandleChecked();
-    result = AbsoluteAndNot(isolate, result, x, *result);
-    return AbsoluteAddOne(isolate, result, true, *result);
   }
+  return MutableBigInt::MakeImmutable(result);
 }
 
 MaybeHandle<BigInt> BigInt::Increment(Isolate* isolate, Handle<BigInt> x) {
@@ -1270,16 +1222,12 @@ MaybeHandle<MutableBigInt> MutableBigInt::AbsoluteAddOne(
   } else {
     DCHECK(result->length() == result_length);
   }
-  digit_t carry = 1;
+  if (input_length == 0) {
-  for (int i = 0; i < input_length; i++) {
+    result->set_digit(0, 1);
-    digit_t new_carry = 0;
+  } else if (input_length == 1 && !will_overflow) {
-    result->set_digit(i, digit_add(x->digit(i), carry, &new_carry));
+    result->set_digit(0, x->digit(0) + 1);
-    carry = new_carry;
-  }
-  if (result_length > input_length) {
-    result->set_digit(input_length, carry);
   } else {
-    DCHECK_EQ(carry, 0);
+    bigint::AddOne(GetRWDigits(result), GetDigits(x));
   }
   result->set_sign(sign);
   return result;
@@ -1289,134 +1237,16 @@ MaybeHandle<MutableBigInt> MutableBigInt::AbsoluteAddOne(
 Handle<MutableBigInt> MutableBigInt::AbsoluteSubOne(Isolate* isolate,
                                                     Handle<BigIntBase> x) {
   DCHECK(!x->is_zero());
-  // Requesting a result length identical to an existing BigInt's length
-  // cannot overflow the limit.
-  return AbsoluteSubOne(isolate, x, x->length()).ToHandleChecked();
-}
-
-// Like the above, but you can specify that the allocated result should have
-// length {result_length}, which must be at least as large as {x->length()}.
-MaybeHandle<MutableBigInt> MutableBigInt::AbsoluteSubOne(Isolate* isolate,
-                                                         Handle<BigIntBase> x,
-                                                         int result_length) {
-  DCHECK(!x->is_zero());
-  DCHECK(result_length >= x->length());
-  Handle<MutableBigInt> result;
-  if (!New(isolate, result_length).ToHandle(&result)) {
-    return MaybeHandle<MutableBigInt>();
-  }
   int length = x->length();
-  digit_t borrow = 1;
+  Handle<MutableBigInt> result = New(isolate, length).ToHandleChecked();
-  for (int i = 0; i < length; i++) {
+  if (length == 1) {
-    digit_t new_borrow = 0;
+    result->set_digit(0, x->digit(0) - 1);
-    result->set_digit(i, digit_sub(x->digit(i), borrow, &new_borrow));
-    borrow = new_borrow;
-  }
-  DCHECK_EQ(borrow, 0);
-  for (int i = length; i < result_length; i++) {
-    result->set_digit(i, borrow);
-  }
-  return result;
-}
-
-// Helper for Absolute{And,AndNot,Or,Xor}.
-// Performs the given binary {op} on digit pairs of {x} and {y}; when the
-// end of the shorter of the two is reached, {extra_digits} configures how
-// remaining digits in the longer input (if {symmetric} == kSymmetric, in
-// {x} otherwise) are handled: copied to the result or ignored.
-// If {result_storage} is non-nullptr, it will be used for the result and
-// any extra digits in it will be zeroed out, otherwise a new BigInt (with
-// the same length as the longer input) will be allocated.
-// {result_storage} may alias {x} or {y} for in-place modification.
-// Example:
-//              y:             [ y2 ][ y1 ][ y0 ]
-//              x:       [ x3 ][ x2 ][ x1 ][ x0 ]
-//                          |     |     |     |
-//                      (kCopy)  (op)  (op)  (op)
-//                          |     |     |     |
-//                          v     v     v     v
-// result_storage: [  0 ][ x3 ][ r2 ][ r1 ][ r0 ]
-inline Handle<MutableBigInt> MutableBigInt::AbsoluteBitwiseOp(
-    Isolate* isolate, Handle<BigIntBase> x, Handle<BigIntBase> y,
-    MutableBigInt result_storage, ExtraDigitsHandling extra_digits,
-    SymmetricOp symmetric, const std::function<digit_t(digit_t, digit_t)>& op) {
-  int x_length = x->length();
-  int y_length = y->length();
-  int num_pairs = y_length;
-  if (x_length < y_length) {
-    num_pairs = x_length;
-    if (symmetric == kSymmetric) {
-      std::swap(x, y);
-      std::swap(x_length, y_length);
-    }
-  }
-  DCHECK(num_pairs == std::min(x_length, y_length));
-  Handle<MutableBigInt> result(result_storage, isolate);
-  int result_length = extra_digits == kCopy ? x_length : num_pairs;
-  if (result_storage.is_null()) {
-    result = New(isolate, result_length).ToHandleChecked();
   } else {
-    DCHECK(result_storage.length() >= result_length);
+    bigint::SubtractOne(GetRWDigits(result), GetDigits(x));
-    result_length = result_storage.length();
-  }
-  int i = 0;
-  for (; i < num_pairs; i++) {
-    result->set_digit(i, op(x->digit(i), y->digit(i)));
-  }
-  if (extra_digits == kCopy) {
-    for (; i < x_length; i++) {
-      result->set_digit(i, x->digit(i));
-    }
-  }
-  for (; i < result_length; i++) {
-    result->set_digit(i, 0);
   }
   return result;
 }
 
-// If {result_storage} is non-nullptr, it will be used for the result,
-// otherwise a new BigInt of appropriate length will be allocated.
-// {result_storage} may alias {x} or {y} for in-place modification.
-Handle<MutableBigInt> MutableBigInt::AbsoluteAnd(Isolate* isolate,
-                                                 Handle<BigIntBase> x,
-                                                 Handle<BigIntBase> y,
-                                                 MutableBigInt result_storage) {
-  return AbsoluteBitwiseOp(isolate, x, y, result_storage, kSkip, kSymmetric,
-                           [](digit_t a, digit_t b) { return a & b; });
-}
-
-// If {result_storage} is non-nullptr, it will be used for the result,
-// otherwise a new BigInt of appropriate length will be allocated.
-// {result_storage} may alias {x} or {y} for in-place modification.
-Handle<MutableBigInt> MutableBigInt::AbsoluteAndNot(
-    Isolate* isolate, Handle<BigIntBase> x, Handle<BigIntBase> y,
-    MutableBigInt result_storage) {
-  return AbsoluteBitwiseOp(isolate, x, y, result_storage, kCopy, kNotSymmetric,
-                           [](digit_t a, digit_t b) { return a & ~b; });
-}
-
-// If {result_storage} is non-nullptr, it will be used for the result,
-// otherwise a new BigInt of appropriate length will be allocated.
-// {result_storage} may alias {x} or {y} for in-place modification.
-Handle<MutableBigInt> MutableBigInt::AbsoluteOr(Isolate* isolate,
-                                                Handle<BigIntBase> x,
-                                                Handle<BigIntBase> y,
-                                                MutableBigInt result_storage) {
-  return AbsoluteBitwiseOp(isolate, x, y, result_storage, kCopy, kSymmetric,
-                           [](digit_t a, digit_t b) { return a | b; });
-}
-
-// If {result_storage} is non-nullptr, it will be used for the result,
-// otherwise a new BigInt of appropriate length will be allocated.
-// {result_storage} may alias {x} or {y} for in-place modification.
-Handle<MutableBigInt> MutableBigInt::AbsoluteXor(Isolate* isolate,
-                                                 Handle<BigIntBase> x,
-                                                 Handle<BigIntBase> y,
-                                                 MutableBigInt result_storage) {
-  return AbsoluteBitwiseOp(isolate, x, y, result_storage, kCopy, kSymmetric,
-                           [](digit_t a, digit_t b) { return a ^ b; });
-}
-
 MaybeHandle<BigInt> MutableBigInt::LeftShiftByAbsolute(Isolate* isolate,
                                                        Handle<BigIntBase> x,
                                                        Handle<BigIntBase> y) {
@@ -1950,21 +1780,6 @@ using twodigit_t = uint64_t;
 using twodigit_t = __uint128_t;
 #endif
 
-// {carry} must point to an initialized digit_t and will either be incremented
-// by one or left alone.
-inline BigInt::digit_t MutableBigInt::digit_add(digit_t a, digit_t b,
-                                                digit_t* carry) {
-#if HAVE_TWODIGIT_T
-  twodigit_t result = static_cast<twodigit_t>(a) + static_cast<twodigit_t>(b);
-  *carry += result >> kDigitBits;
-  return static_cast<digit_t>(result);
-#else
-  digit_t result = a + b;
-  if (result < a) *carry += 1;
-  return result;
-#endif
-}
-
 // {borrow} must point to an initialized digit_t and will either be incremented
 // by one or left alone.
 inline BigInt::digit_t MutableBigInt::digit_sub(digit_t a, digit_t b,