[bigint] Implement Add, Subtract, UnaryMinus
Bug: v8:6791 Change-Id: I058db23c03451dc5028c3d39af8607d31048295c Reviewed-on: https://chromium-review.googlesource.com/667809 Commit-Queue: Jakob Kummerow <jkummerow@chromium.org> Reviewed-by: Georg Neis <neis@chromium.org> Cr-Commit-Position: refs/heads/master@{#48075}
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Jakob Kummerow
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@ -2,6 +2,21 @@
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Parts of the implementation below:
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// Copyright (c) 2014 the Dart project authors. Please see the AUTHORS file [1]
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file [2].
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//
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// [1] https://github.com/dart-lang/sdk/blob/master/AUTHORS
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// [2] https://github.com/dart-lang/sdk/blob/master/LICENSE
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file [3].
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//
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// [3] https://golang.org/LICENSE
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#include "src/objects/bigint.h"
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#include "src/objects-inl.h"
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@ -10,7 +25,13 @@ namespace v8 {
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namespace internal {
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Handle<BigInt> BigInt::UnaryMinus(Handle<BigInt> x) {
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UNIMPLEMENTED(); // TODO(jkummerow): Implement.
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// Special case: There is no -0n.
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if (x->is_zero()) {
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return x;
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}
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Handle<BigInt> result = BigInt::Copy(x);
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result->set_sign(!x->sign());
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return result;
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}
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Handle<BigInt> BigInt::BitwiseNot(Handle<BigInt> x) {
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@ -35,11 +56,33 @@ MaybeHandle<BigInt> BigInt::Remainder(Handle<BigInt> x, Handle<BigInt> y) {
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}
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Handle<BigInt> BigInt::Add(Handle<BigInt> x, Handle<BigInt> y) {
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UNIMPLEMENTED(); // TODO(jkummerow): Implement.
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bool xsign = x->sign();
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if (xsign == y->sign()) {
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// x + y == x + y
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// -x + -y == -(x + y)
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return AbsoluteAdd(x, y, xsign);
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}
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// x + -y == x - y == -(y - x)
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// -x + y == y - x == -(x - y)
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if (AbsoluteCompare(x, y) >= 0) {
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return AbsoluteSub(x, y, xsign);
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}
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return AbsoluteSub(y, x, !xsign);
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}
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Handle<BigInt> BigInt::Subtract(Handle<BigInt> x, Handle<BigInt> y) {
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UNIMPLEMENTED(); // TODO(jkummerow): Implement.
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bool xsign = x->sign();
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if (xsign != y->sign()) {
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// x - (-y) == x + y
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// (-x) - y == -(x + y)
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return AbsoluteAdd(x, y, xsign);
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}
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// x - y == -(y - x)
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// (-x) - (-y) == y - x == -(x - y)
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if (AbsoluteCompare(x, y) >= 0) {
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return AbsoluteSub(x, y, xsign);
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}
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return AbsoluteSub(y, x, !xsign);
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}
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Handle<BigInt> BigInt::LeftShift(Handle<BigInt> x, Handle<BigInt> y) {
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@ -83,7 +126,7 @@ Handle<BigInt> BigInt::BitwiseOr(Handle<BigInt> x, Handle<BigInt> y) {
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Handle<String> BigInt::ToString(Handle<BigInt> bigint, int radix) {
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// TODO(jkummerow): Support non-power-of-two radixes.
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if (!base::bits::IsPowerOfTwo(radix)) radix = 16;
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return bigint->ToStringBasePowerOfTwo(bigint, radix);
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return ToStringBasePowerOfTwo(bigint, radix);
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}
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void BigInt::Initialize(int length, bool zero_initialize) {
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@ -104,6 +147,105 @@ void BigInt::Initialize(int length, bool zero_initialize) {
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// Private helpers for public methods.
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Handle<BigInt> BigInt::AbsoluteAdd(Handle<BigInt> x, Handle<BigInt> y,
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bool result_sign) {
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if (x->length() < y->length()) return AbsoluteAdd(y, x, result_sign);
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if (x->is_zero()) {
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DCHECK(y->is_zero());
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return x;
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}
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if (y->is_zero()) {
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return result_sign == x->sign() ? x : UnaryMinus(x);
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}
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Handle<BigInt> result =
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x->GetIsolate()->factory()->NewBigIntRaw(x->length() + 1);
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digit_t carry = 0;
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int i = 0;
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for (; i < y->length(); i++) {
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digit_t new_carry = 0;
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digit_t sum = digit_add(x->digit(i), y->digit(i), &new_carry);
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sum = digit_add(sum, carry, &new_carry);
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result->set_digit(i, sum);
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carry = new_carry;
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}
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for (; i < x->length(); i++) {
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digit_t new_carry = 0;
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digit_t sum = digit_add(x->digit(i), carry, &new_carry);
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result->set_digit(i, sum);
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carry = new_carry;
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}
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result->set_digit(i, carry);
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result->set_sign(result_sign);
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result->RightTrim();
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return result;
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}
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Handle<BigInt> BigInt::AbsoluteSub(Handle<BigInt> x, Handle<BigInt> y,
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bool result_sign) {
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DCHECK(x->length() >= y->length());
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SLOW_DCHECK(AbsoluteCompare(x, y) >= 0);
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if (x->is_zero()) {
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DCHECK(y->is_zero());
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return x;
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}
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if (y->is_zero()) {
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return result_sign == x->sign() ? x : UnaryMinus(x);
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}
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Handle<BigInt> result = x->GetIsolate()->factory()->NewBigIntRaw(x->length());
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digit_t borrow = 0;
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int i = 0;
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for (; i < y->length(); i++) {
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digit_t new_borrow = 0;
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digit_t difference = digit_sub(x->digit(i), y->digit(i), &new_borrow);
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difference = digit_sub(difference, borrow, &new_borrow);
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result->set_digit(i, difference);
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borrow = new_borrow;
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}
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for (; i < x->length(); i++) {
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digit_t new_borrow = 0;
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digit_t difference = digit_sub(x->digit(i), borrow, &new_borrow);
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result->set_digit(i, difference);
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borrow = new_borrow;
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}
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DCHECK_EQ(0, borrow);
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result->set_sign(result_sign);
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result->RightTrim();
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return result;
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}
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int BigInt::AbsoluteCompare(Handle<BigInt> x, Handle<BigInt> y) {
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int diff = x->length() - y->length();
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if (diff != 0) return diff;
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int i = x->length() - 1;
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while (i >= 0 && x->digit(i) == y->digit(i)) i--;
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if (i < 0) return 0;
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return x->digit(i) > y->digit(i) ? 1 : -1;
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}
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Handle<BigInt> BigInt::Copy(Handle<BigInt> source) {
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int length = source->length();
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Handle<BigInt> result = source->GetIsolate()->factory()->NewBigIntRaw(length);
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memcpy(result->address() + HeapObject::kHeaderSize,
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source->address() + HeapObject::kHeaderSize,
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SizeFor(length) - HeapObject::kHeaderSize);
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return result;
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}
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void BigInt::RightTrim() {
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int old_length = length();
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int new_length = old_length;
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while (digit(new_length - 1) == 0) new_length--;
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int to_trim = old_length - new_length;
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if (to_trim == 0) return;
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int size_delta = to_trim * kDigitSize;
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Address new_end = this->address() + SizeFor(new_length);
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Heap* heap = GetHeap();
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heap->CreateFillerObjectAt(new_end, size_delta, ClearRecordedSlots::kNo);
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// Canonicalize -0n.
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if (new_length == 0) set_sign(false);
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set_length(new_length);
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}
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static const char kConversionChars[] = "0123456789abcdefghijklmnopqrstuvwxyz";
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// TODO(jkummerow): Add more tests for this when it is exposed on
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@ -114,7 +256,7 @@ Handle<String> BigInt::ToStringBasePowerOfTwo(Handle<BigInt> x, int radix) {
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DCHECK(radix >= 2 && radix <= 32);
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Factory* factory = x->GetIsolate()->factory();
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// TODO(jkummerow): check in caller?
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if (is_zero()) return factory->NewStringFromStaticChars("0");
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if (x->is_zero()) return factory->NewStringFromStaticChars("0");
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const int len = x->length();
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const bool sign = x->sign();
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@ -128,6 +270,9 @@ Handle<String> BigInt::ToStringBasePowerOfTwo(Handle<BigInt> x, int radix) {
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chars_for_msd++;
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}
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// All other digits need chars_per_digit characters; a leading "-" needs one.
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if ((String::kMaxLength - chars_for_msd - sign) / chars_per_digit < len - 1) {
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CHECK(false); // TODO(jkummerow): Throw instead of crashing.
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}
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const int chars = chars_for_msd + (len - 1) * chars_per_digit + sign;
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Handle<SeqOneByteString> result =
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@ -151,6 +296,48 @@ Handle<String> BigInt::ToStringBasePowerOfTwo(Handle<BigInt> x, int radix) {
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return result;
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}
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// Digit arithmetic helpers.
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#if V8_TARGET_ARCH_32_BIT
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#define HAVE_TWODIGIT_T 1
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typedef uint64_t twodigit_t;
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#elif defined(__SIZEOF_INT128__)
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// Both Clang and GCC support this on x64.
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#define HAVE_TWODIGIT_T 1
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typedef __uint128_t twodigit_t;
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#endif
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// {carry} must point to an initialized digit_t and will either be incremented
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// by one or left alone.
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inline BigInt::digit_t BigInt::digit_add(digit_t a, digit_t b, digit_t* carry) {
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#if HAVE_TWODIGIT_T
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twodigit_t result = static_cast<twodigit_t>(a) + static_cast<twodigit_t>(b);
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*carry += result >> kDigitBits;
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return static_cast<digit_t>(result);
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#else
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digit_t result = a + b;
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if (result < a) *carry += 1;
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return result;
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#endif
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}
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// {borrow} must point to an initialized digit_t and will either be incremented
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// by one or left alone.
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inline BigInt::digit_t BigInt::digit_sub(digit_t a, digit_t b,
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digit_t* borrow) {
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#if HAVE_TWODIGIT_T
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twodigit_t result = static_cast<twodigit_t>(a) - static_cast<twodigit_t>(b);
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*borrow += (result >> kDigitBits) & 1;
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return static_cast<digit_t>(result);
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#else
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digit_t result = a - b;
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if (result > a) *borrow += 1;
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return static_cast<digit_t>(result);
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#endif
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}
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#undef HAVE_TWODIGIT_T
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#ifdef OBJECT_PRINT
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void BigInt::BigIntPrint(std::ostream& os) {
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DisallowHeapAllocation no_gc;
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@ -89,7 +89,22 @@ class BigInt : public HeapObject {
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static const digit_t kHalfDigitMask = (1ull << kHalfDigitBits) - 1;
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// Private helpers for public methods.
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Handle<String> ToStringBasePowerOfTwo(Handle<BigInt> x, int radix);
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static Handle<BigInt> Copy(Handle<BigInt> source);
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void RightTrim();
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static Handle<BigInt> AbsoluteAdd(Handle<BigInt> x, Handle<BigInt> y,
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bool result_sign);
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static Handle<BigInt> AbsoluteSub(Handle<BigInt> x, Handle<BigInt> y,
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bool result_sign);
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// Returns a positive value if abs(x) > abs(y), a negative value if
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// abs(x) < abs(y), or zero if abs(x) == abs(y).
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static int AbsoluteCompare(Handle<BigInt> x, Handle<BigInt> y);
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static Handle<String> ToStringBasePowerOfTwo(Handle<BigInt> x, int radix);
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// Digit arithmetic helpers.
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static inline digit_t digit_add(digit_t a, digit_t b, digit_t* carry);
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static inline digit_t digit_sub(digit_t a, digit_t b, digit_t* borrow);
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class LengthBits : public BitField<int, 0, kMaxLengthBits> {};
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class SignBits : public BitField<bool, LengthBits::kNext, 1> {};
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