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b9b6511ca6
Closes https://github.com/dart-lang/sdk/pull/50918 Co-authored-by: Josh Soref <jsoref@gmail.com> GitOrigin-RevId: 1fd275051c561b63d374fb47e76a22424c4a12a9 Change-Id: I97790d9c79ff659f2c1fa2d2d46d041fe67957cb Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/278530 Reviewed-by: William Hesse <whesse@google.com> Commit-Queue: Alexander Thomas <athom@google.com> Reviewed-by: Tess Strickland <sstrickl@google.com>
84 lines
2.8 KiB
Dart
84 lines
2.8 KiB
Dart
// Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
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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.
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// Testing Bigints with and without intrinsics.
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// VMOptions=--intrinsify --no-enable-asserts
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// VMOptions=--intrinsify --enable-asserts
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// VMOptions=--no-intrinsify --enable-asserts
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// VMOptions=--no-intrinsify --no-enable-asserts
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import "package:expect/expect.dart";
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const debugPrint = bool.fromEnvironment('debugPrint');
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void check(int length, BigInt base) {
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assert(length >= 5);
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assert(base > BigInt.zero);
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// Check with slight adjustments. We choose -3..+3 so that the lowest bit in
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// the 2's-complement representation is both zero and one for both the
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// positive [n] and its negative complement [m] below.
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for (int delta = -3; delta <= 3; delta++) {
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BigInt n = base + BigInt.from(delta);
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assert(n >= BigInt.zero);
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// Compute the bitLength by shifting the value into a small integer range
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// and adjust the `int.bitLength` value by the shift count.
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int shiftCount = length - 5;
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int shiftedN = (n >> shiftCount).toInt();
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int expectedLength = shiftCount + shiftedN.bitLength;
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int nLength = n.bitLength;
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Expect.equals(expectedLength, nLength);
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// Use identity `x.bitLength == (-x-1).bitLength` to check negative values.
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BigInt m = -n - BigInt.one;
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int mLength = m.bitLength;
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if (debugPrint) {
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final printLength = length + 4;
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final nDigits =
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n.toUnsigned(printLength).toRadixString(2).padLeft(printLength);
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final mDigits = m.toUnsigned(printLength).toRadixString(2);
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print('$nDigits: $nLength');
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print('$mDigits: $mLength');
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}
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Expect.equals(nLength, mLength);
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}
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}
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void main() {
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// For small values, [BigInt.bitLength] should be the same as [int.bitLength].
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for (int i = 0; i <= 64; i++) {
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Expect.equals(i.bitLength, BigInt.from(i).bitLength);
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// Note: This is not quite redundant for `i==0` since on the web platform
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// `-i` is negative zero and not the same as `0-i`.
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Expect.equals((-i).bitLength, BigInt.from(-i).bitLength);
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}
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// Test x.bitLength for a large variety of lengths.
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for (int length = 5; length <= 512; length++) {
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BigInt base = BigInt.one << (length - 1);
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Expect.equals(length, base.bitLength);
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// Power of two.
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check(length, base);
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// Two high bits set.
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check(length, base | base >> 1);
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// Check for values with an additional bit set near a potential internal
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// digit boundary.
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for (int i1 = 16; i1 < length; i1 += 16) {
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for (int i2 = -1; i2 <= 1; i2++) {
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int i = i1 + i2;
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if (i < length - 1) {
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check(length, base | BigInt.one << (i - 1));
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}
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}
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}
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}
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}
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