001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.primitives;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkElementIndex;
019import static com.google.common.base.Preconditions.checkNotNull;
020import static com.google.common.base.Preconditions.checkPositionIndexes;
021import static com.google.common.base.Strings.lenientFormat;
022import static java.lang.Double.NEGATIVE_INFINITY;
023import static java.lang.Double.POSITIVE_INFINITY;
024
025import com.google.common.annotations.GwtCompatible;
026import com.google.common.annotations.GwtIncompatible;
027import com.google.common.annotations.J2ktIncompatible;
028import com.google.common.base.Converter;
029import java.io.Serializable;
030import java.util.AbstractList;
031import java.util.Arrays;
032import java.util.Collection;
033import java.util.Collections;
034import java.util.Comparator;
035import java.util.List;
036import java.util.RandomAccess;
037import javax.annotation.CheckForNull;
038
039/**
040 * Static utility methods pertaining to {@code double} primitives, that are not already found in
041 * either {@link Double} or {@link Arrays}.
042 *
043 * <p>See the Guava User Guide article on <a
044 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
045 *
046 * @author Kevin Bourrillion
047 * @since 1.0
048 */
049@GwtCompatible(emulated = true)
050@ElementTypesAreNonnullByDefault
051public final class Doubles extends DoublesMethodsForWeb {
052  private Doubles() {}
053
054  /**
055   * The number of bytes required to represent a primitive {@code double} value.
056   *
057   * <p><b>Java 8+ users:</b> use {@link Double#BYTES} instead.
058   *
059   * @since 10.0
060   */
061  public static final int BYTES = Double.SIZE / Byte.SIZE;
062
063  /**
064   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Double)
065   * value).hashCode()}.
066   *
067   * <p><b>Java 8+ users:</b> use {@link Double#hashCode(double)} instead.
068   *
069   * @param value a primitive {@code double} value
070   * @return a hash code for the value
071   */
072  public static int hashCode(double value) {
073    return ((Double) value).hashCode();
074    // TODO(kevinb): do it this way when we can (GWT problem):
075    // long bits = Double.doubleToLongBits(value);
076    // return (int) (bits ^ (bits >>> 32));
077  }
078
079  /**
080   * Compares the two specified {@code double} values. The sign of the value returned is the same as
081   * that of <code>((Double) a).{@linkplain Double#compareTo compareTo}(b)</code>. As with that
082   * method, {@code NaN} is treated as greater than all other values, and {@code 0.0 > -0.0}.
083   *
084   * <p><b>Note:</b> this method simply delegates to the JDK method {@link Double#compare}. It is
085   * provided for consistency with the other primitive types, whose compare methods were not added
086   * to the JDK until JDK 7.
087   *
088   * @param a the first {@code double} to compare
089   * @param b the second {@code double} to compare
090   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
091   *     greater than {@code b}; or zero if they are equal
092   */
093  public static int compare(double a, double b) {
094    return Double.compare(a, b);
095  }
096
097  /**
098   * Returns {@code true} if {@code value} represents a real number. This is equivalent to, but not
099   * necessarily implemented as, {@code !(Double.isInfinite(value) || Double.isNaN(value))}.
100   *
101   * <p><b>Java 8+ users:</b> use {@link Double#isFinite(double)} instead.
102   *
103   * @since 10.0
104   */
105  public static boolean isFinite(double value) {
106    return NEGATIVE_INFINITY < value && value < POSITIVE_INFINITY;
107  }
108
109  /**
110   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}. Note
111   * that this always returns {@code false} when {@code target} is {@code NaN}.
112   *
113   * @param array an array of {@code double} values, possibly empty
114   * @param target a primitive {@code double} value
115   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
116   */
117  public static boolean contains(double[] array, double target) {
118    for (double value : array) {
119      if (value == target) {
120        return true;
121      }
122    }
123    return false;
124  }
125
126  /**
127   * Returns the index of the first appearance of the value {@code target} in {@code array}. Note
128   * that this always returns {@code -1} when {@code target} is {@code NaN}.
129   *
130   * @param array an array of {@code double} values, possibly empty
131   * @param target a primitive {@code double} value
132   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
133   *     such index exists.
134   */
135  public static int indexOf(double[] array, double target) {
136    return indexOf(array, target, 0, array.length);
137  }
138
139  // TODO(kevinb): consider making this public
140  private static int indexOf(double[] array, double target, int start, int end) {
141    for (int i = start; i < end; i++) {
142      if (array[i] == target) {
143        return i;
144      }
145    }
146    return -1;
147  }
148
149  /**
150   * Returns the start position of the first occurrence of the specified {@code target} within
151   * {@code array}, or {@code -1} if there is no such occurrence.
152   *
153   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
154   * i, i + target.length)} contains exactly the same elements as {@code target}.
155   *
156   * <p>Note that this always returns {@code -1} when {@code target} contains {@code NaN}.
157   *
158   * @param array the array to search for the sequence {@code target}
159   * @param target the array to search for as a sub-sequence of {@code array}
160   */
161  public static int indexOf(double[] array, double[] target) {
162    checkNotNull(array, "array");
163    checkNotNull(target, "target");
164    if (target.length == 0) {
165      return 0;
166    }
167
168    outer:
169    for (int i = 0; i < array.length - target.length + 1; i++) {
170      for (int j = 0; j < target.length; j++) {
171        if (array[i + j] != target[j]) {
172          continue outer;
173        }
174      }
175      return i;
176    }
177    return -1;
178  }
179
180  /**
181   * Returns the index of the last appearance of the value {@code target} in {@code array}. Note
182   * that this always returns {@code -1} when {@code target} is {@code NaN}.
183   *
184   * @param array an array of {@code double} values, possibly empty
185   * @param target a primitive {@code double} value
186   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
187   *     such index exists.
188   */
189  public static int lastIndexOf(double[] array, double target) {
190    return lastIndexOf(array, target, 0, array.length);
191  }
192
193  // TODO(kevinb): consider making this public
194  private static int lastIndexOf(double[] array, double target, int start, int end) {
195    for (int i = end - 1; i >= start; i--) {
196      if (array[i] == target) {
197        return i;
198      }
199    }
200    return -1;
201  }
202
203  /**
204   * Returns the least value present in {@code array}, using the same rules of comparison as {@link
205   * Math#min(double, double)}.
206   *
207   * @param array a <i>nonempty</i> array of {@code double} values
208   * @return the value present in {@code array} that is less than or equal to every other value in
209   *     the array
210   * @throws IllegalArgumentException if {@code array} is empty
211   */
212  @GwtIncompatible(
213      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
214  public static double min(double... array) {
215    checkArgument(array.length > 0);
216    double min = array[0];
217    for (int i = 1; i < array.length; i++) {
218      min = Math.min(min, array[i]);
219    }
220    return min;
221  }
222
223  /**
224   * Returns the greatest value present in {@code array}, using the same rules of comparison as
225   * {@link Math#max(double, double)}.
226   *
227   * @param array a <i>nonempty</i> array of {@code double} values
228   * @return the value present in {@code array} that is greater than or equal to every other value
229   *     in the array
230   * @throws IllegalArgumentException if {@code array} is empty
231   */
232  @GwtIncompatible(
233      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
234  public static double max(double... array) {
235    checkArgument(array.length > 0);
236    double max = array[0];
237    for (int i = 1; i < array.length; i++) {
238      max = Math.max(max, array[i]);
239    }
240    return max;
241  }
242
243  /**
244   * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
245   *
246   * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
247   * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
248   * value} is greater than {@code max}, {@code max} is returned.
249   *
250   * @param value the {@code double} value to constrain
251   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
252   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
253   * @throws IllegalArgumentException if {@code min > max}
254   * @since 21.0
255   */
256  public static double constrainToRange(double value, double min, double max) {
257    // avoid auto-boxing by not using Preconditions.checkArgument(); see Guava issue 3984
258    // Reject NaN by testing for the good case (min <= max) instead of the bad (min > max).
259    if (min <= max) {
260      return Math.min(Math.max(value, min), max);
261    }
262    throw new IllegalArgumentException(
263        lenientFormat("min (%s) must be less than or equal to max (%s)", min, max));
264  }
265
266  /**
267   * Returns the values from each provided array combined into a single array. For example, {@code
268   * concat(new double[] {a, b}, new double[] {}, new double[] {c}} returns the array {@code {a, b,
269   * c}}.
270   *
271   * @param arrays zero or more {@code double} arrays
272   * @return a single array containing all the values from the source arrays, in order
273   */
274  public static double[] concat(double[]... arrays) {
275    int length = 0;
276    for (double[] array : arrays) {
277      length += array.length;
278    }
279    double[] result = new double[length];
280    int pos = 0;
281    for (double[] array : arrays) {
282      System.arraycopy(array, 0, result, pos, array.length);
283      pos += array.length;
284    }
285    return result;
286  }
287
288  private static final class DoubleConverter extends Converter<String, Double>
289      implements Serializable {
290    static final Converter<String, Double> INSTANCE = new DoubleConverter();
291
292    @Override
293    protected Double doForward(String value) {
294      return Double.valueOf(value);
295    }
296
297    @Override
298    protected String doBackward(Double value) {
299      return value.toString();
300    }
301
302    @Override
303    public String toString() {
304      return "Doubles.stringConverter()";
305    }
306
307    private Object readResolve() {
308      return INSTANCE;
309    }
310
311    private static final long serialVersionUID = 1;
312  }
313
314  /**
315   * Returns a serializable converter object that converts between strings and doubles using {@link
316   * Double#valueOf} and {@link Double#toString()}.
317   *
318   * @since 16.0
319   */
320  public static Converter<String, Double> stringConverter() {
321    return DoubleConverter.INSTANCE;
322  }
323
324  /**
325   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
326   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
327   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
328   * returned, containing the values of {@code array}, and zeroes in the remaining places.
329   *
330   * @param array the source array
331   * @param minLength the minimum length the returned array must guarantee
332   * @param padding an extra amount to "grow" the array by if growth is necessary
333   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
334   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
335   *     minLength}
336   */
337  public static double[] ensureCapacity(double[] array, int minLength, int padding) {
338    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
339    checkArgument(padding >= 0, "Invalid padding: %s", padding);
340    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
341  }
342
343  /**
344   * Returns a string containing the supplied {@code double} values, converted to strings as
345   * specified by {@link Double#toString(double)}, and separated by {@code separator}. For example,
346   * {@code join("-", 1.0, 2.0, 3.0)} returns the string {@code "1.0-2.0-3.0"}.
347   *
348   * <p>Note that {@link Double#toString(double)} formats {@code double} differently in GWT
349   * sometimes. In the previous example, it returns the string {@code "1-2-3"}.
350   *
351   * @param separator the text that should appear between consecutive values in the resulting string
352   *     (but not at the start or end)
353   * @param array an array of {@code double} values, possibly empty
354   */
355  public static String join(String separator, double... array) {
356    checkNotNull(separator);
357    if (array.length == 0) {
358      return "";
359    }
360
361    // For pre-sizing a builder, just get the right order of magnitude
362    StringBuilder builder = new StringBuilder(array.length * 12);
363    builder.append(array[0]);
364    for (int i = 1; i < array.length; i++) {
365      builder.append(separator).append(array[i]);
366    }
367    return builder.toString();
368  }
369
370  /**
371   * Returns a comparator that compares two {@code double} arrays <a
372   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
373   * compares, using {@link #compare(double, double)}), the first pair of values that follow any
374   * common prefix, or when one array is a prefix of the other, treats the shorter array as the
375   * lesser. For example, {@code [] < [1.0] < [1.0, 2.0] < [2.0]}.
376   *
377   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
378   * support only identity equality), but it is consistent with {@link Arrays#equals(double[],
379   * double[])}.
380   *
381   * @since 2.0
382   */
383  public static Comparator<double[]> lexicographicalComparator() {
384    return LexicographicalComparator.INSTANCE;
385  }
386
387  private enum LexicographicalComparator implements Comparator<double[]> {
388    INSTANCE;
389
390    @Override
391    public int compare(double[] left, double[] right) {
392      int minLength = Math.min(left.length, right.length);
393      for (int i = 0; i < minLength; i++) {
394        int result = Double.compare(left[i], right[i]);
395        if (result != 0) {
396          return result;
397        }
398      }
399      return left.length - right.length;
400    }
401
402    @Override
403    public String toString() {
404      return "Doubles.lexicographicalComparator()";
405    }
406  }
407
408  /**
409   * Sorts the elements of {@code array} in descending order.
410   *
411   * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats
412   * all NaN values as equal and 0.0 as greater than -0.0.
413   *
414   * @since 23.1
415   */
416  public static void sortDescending(double[] array) {
417    checkNotNull(array);
418    sortDescending(array, 0, array.length);
419  }
420
421  /**
422   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
423   * exclusive in descending order.
424   *
425   * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats
426   * all NaN values as equal and 0.0 as greater than -0.0.
427   *
428   * @since 23.1
429   */
430  public static void sortDescending(double[] array, int fromIndex, int toIndex) {
431    checkNotNull(array);
432    checkPositionIndexes(fromIndex, toIndex, array.length);
433    Arrays.sort(array, fromIndex, toIndex);
434    reverse(array, fromIndex, toIndex);
435  }
436
437  /**
438   * Reverses the elements of {@code array}. This is equivalent to {@code
439   * Collections.reverse(Doubles.asList(array))}, but is likely to be more efficient.
440   *
441   * @since 23.1
442   */
443  public static void reverse(double[] array) {
444    checkNotNull(array);
445    reverse(array, 0, array.length);
446  }
447
448  /**
449   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
450   * exclusive. This is equivalent to {@code
451   * Collections.reverse(Doubles.asList(array).subList(fromIndex, toIndex))}, but is likely to be
452   * more efficient.
453   *
454   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
455   *     {@code toIndex > fromIndex}
456   * @since 23.1
457   */
458  public static void reverse(double[] array, int fromIndex, int toIndex) {
459    checkNotNull(array);
460    checkPositionIndexes(fromIndex, toIndex, array.length);
461    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
462      double tmp = array[i];
463      array[i] = array[j];
464      array[j] = tmp;
465    }
466  }
467
468  /**
469   * Performs a right rotation of {@code array} of "distance" places, so that the first element is
470   * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance
471   * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Bytes.asList(array),
472   * distance)}, but is considerably faster and avoids allocation and garbage collection.
473   *
474   * <p>The provided "distance" may be negative, which will rotate left.
475   *
476   * @since 32.0.0
477   */
478  public static void rotate(double[] array, int distance) {
479    rotate(array, distance, 0, array.length);
480  }
481
482  /**
483   * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code
484   * toIndex} exclusive. This is equivalent to {@code
485   * Collections.rotate(Bytes.asList(array).subList(fromIndex, toIndex), distance)}, but is
486   * considerably faster and avoids allocations and garbage collection.
487   *
488   * <p>The provided "distance" may be negative, which will rotate left.
489   *
490   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
491   *     {@code toIndex > fromIndex}
492   * @since 32.0.0
493   */
494  public static void rotate(double[] array, int distance, int fromIndex, int toIndex) {
495    // See Ints.rotate for more details about possible algorithms here.
496    checkNotNull(array);
497    checkPositionIndexes(fromIndex, toIndex, array.length);
498    if (array.length <= 1) {
499      return;
500    }
501
502    int length = toIndex - fromIndex;
503    // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many
504    // places left to rotate.
505    int m = -distance % length;
506    m = (m < 0) ? m + length : m;
507    // The current index of what will become the first element of the rotated section.
508    int newFirstIndex = m + fromIndex;
509    if (newFirstIndex == fromIndex) {
510      return;
511    }
512
513    reverse(array, fromIndex, newFirstIndex);
514    reverse(array, newFirstIndex, toIndex);
515    reverse(array, fromIndex, toIndex);
516  }
517
518  /**
519   * Returns an array containing each value of {@code collection}, converted to a {@code double}
520   * value in the manner of {@link Number#doubleValue}.
521   *
522   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
523   * Calling this method is as thread-safe as calling that method.
524   *
525   * @param collection a collection of {@code Number} instances
526   * @return an array containing the same values as {@code collection}, in the same order, converted
527   *     to primitives
528   * @throws NullPointerException if {@code collection} or any of its elements is null
529   * @since 1.0 (parameter was {@code Collection<Double>} before 12.0)
530   */
531  public static double[] toArray(Collection<? extends Number> collection) {
532    if (collection instanceof DoubleArrayAsList) {
533      return ((DoubleArrayAsList) collection).toDoubleArray();
534    }
535
536    Object[] boxedArray = collection.toArray();
537    int len = boxedArray.length;
538    double[] array = new double[len];
539    for (int i = 0; i < len; i++) {
540      // checkNotNull for GWT (do not optimize)
541      array[i] = ((Number) checkNotNull(boxedArray[i])).doubleValue();
542    }
543    return array;
544  }
545
546  /**
547   * Returns a fixed-size list backed by the specified array, similar to {@link
548   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
549   * set a value to {@code null} will result in a {@link NullPointerException}.
550   *
551   * <p>The returned list maintains the values, but not the identities, of {@code Double} objects
552   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
553   * the returned list is unspecified.
554   *
555   * <p>The returned list may have unexpected behavior if it contains {@code NaN}, or if {@code NaN}
556   * is used as a parameter to any of its methods.
557   *
558   * <p>The returned list is serializable.
559   *
560   * <p><b>Note:</b> when possible, you should represent your data as an {@link
561   * ImmutableDoubleArray} instead, which has an {@link ImmutableDoubleArray#asList asList} view.
562   *
563   * @param backingArray the array to back the list
564   * @return a list view of the array
565   */
566  public static List<Double> asList(double... backingArray) {
567    if (backingArray.length == 0) {
568      return Collections.emptyList();
569    }
570    return new DoubleArrayAsList(backingArray);
571  }
572
573  @GwtCompatible
574  private static class DoubleArrayAsList extends AbstractList<Double>
575      implements RandomAccess, Serializable {
576    final double[] array;
577    final int start;
578    final int end;
579
580    DoubleArrayAsList(double[] array) {
581      this(array, 0, array.length);
582    }
583
584    DoubleArrayAsList(double[] array, int start, int end) {
585      this.array = array;
586      this.start = start;
587      this.end = end;
588    }
589
590    @Override
591    public int size() {
592      return end - start;
593    }
594
595    @Override
596    public boolean isEmpty() {
597      return false;
598    }
599
600    @Override
601    public Double get(int index) {
602      checkElementIndex(index, size());
603      return array[start + index];
604    }
605
606    @Override
607    public boolean contains(@CheckForNull Object target) {
608      // Overridden to prevent a ton of boxing
609      return (target instanceof Double)
610          && Doubles.indexOf(array, (Double) target, start, end) != -1;
611    }
612
613    @Override
614    public int indexOf(@CheckForNull Object target) {
615      // Overridden to prevent a ton of boxing
616      if (target instanceof Double) {
617        int i = Doubles.indexOf(array, (Double) target, start, end);
618        if (i >= 0) {
619          return i - start;
620        }
621      }
622      return -1;
623    }
624
625    @Override
626    public int lastIndexOf(@CheckForNull Object target) {
627      // Overridden to prevent a ton of boxing
628      if (target instanceof Double) {
629        int i = Doubles.lastIndexOf(array, (Double) target, start, end);
630        if (i >= 0) {
631          return i - start;
632        }
633      }
634      return -1;
635    }
636
637    @Override
638    public Double set(int index, Double element) {
639      checkElementIndex(index, size());
640      double oldValue = array[start + index];
641      // checkNotNull for GWT (do not optimize)
642      array[start + index] = checkNotNull(element);
643      return oldValue;
644    }
645
646    @Override
647    public List<Double> subList(int fromIndex, int toIndex) {
648      int size = size();
649      checkPositionIndexes(fromIndex, toIndex, size);
650      if (fromIndex == toIndex) {
651        return Collections.emptyList();
652      }
653      return new DoubleArrayAsList(array, start + fromIndex, start + toIndex);
654    }
655
656    @Override
657    public boolean equals(@CheckForNull Object object) {
658      if (object == this) {
659        return true;
660      }
661      if (object instanceof DoubleArrayAsList) {
662        DoubleArrayAsList that = (DoubleArrayAsList) object;
663        int size = size();
664        if (that.size() != size) {
665          return false;
666        }
667        for (int i = 0; i < size; i++) {
668          if (array[start + i] != that.array[that.start + i]) {
669            return false;
670          }
671        }
672        return true;
673      }
674      return super.equals(object);
675    }
676
677    @Override
678    public int hashCode() {
679      int result = 1;
680      for (int i = start; i < end; i++) {
681        result = 31 * result + Doubles.hashCode(array[i]);
682      }
683      return result;
684    }
685
686    @Override
687    public String toString() {
688      StringBuilder builder = new StringBuilder(size() * 12);
689      builder.append('[').append(array[start]);
690      for (int i = start + 1; i < end; i++) {
691        builder.append(", ").append(array[i]);
692      }
693      return builder.append(']').toString();
694    }
695
696    double[] toDoubleArray() {
697      return Arrays.copyOfRange(array, start, end);
698    }
699
700    private static final long serialVersionUID = 0;
701  }
702
703  /**
704   * This is adapted from the regex suggested by {@link Double#valueOf(String)} for prevalidating
705   * inputs. All valid inputs must pass this regex, but it's semantically fine if not all inputs
706   * that pass this regex are valid -- only a performance hit is incurred, not a semantics bug.
707   */
708  @J2ktIncompatible @GwtIncompatible // regular expressions
709  static final
710  java.util.regex.Pattern
711      FLOATING_POINT_PATTERN = fpPattern();
712
713  @GwtIncompatible // regular expressions
714  private static
715  java.util.regex.Pattern
716      fpPattern() {
717    /*
718     * We use # instead of * for possessive quantifiers. This lets us strip them out when building
719     * the regex for RE2 (which doesn't support them) but leave them in when building it for
720     * java.util.regex (where we want them in order to avoid catastrophic backtracking).
721     */
722    String decimal = "(?:\\d+#(?:\\.\\d*#)?|\\.\\d+#)";
723    String completeDec = decimal + "(?:[eE][+-]?\\d+#)?[fFdD]?";
724    String hex = "(?:[0-9a-fA-F]+#(?:\\.[0-9a-fA-F]*#)?|\\.[0-9a-fA-F]+#)";
725    String completeHex = "0[xX]" + hex + "[pP][+-]?\\d+#[fFdD]?";
726    String fpPattern = "[+-]?(?:NaN|Infinity|" + completeDec + "|" + completeHex + ")";
727    fpPattern =
728        fpPattern.replace(
729            "#",
730            "+"
731            );
732    return
733    java.util.regex.Pattern
734        .compile(fpPattern);
735  }
736
737  /**
738   * Parses the specified string as a double-precision floating point value. The ASCII character
739   * {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
740   *
741   * <p>Unlike {@link Double#parseDouble(String)}, this method returns {@code null} instead of
742   * throwing an exception if parsing fails. Valid inputs are exactly those accepted by {@link
743   * Double#valueOf(String)}, except that leading and trailing whitespace is not permitted.
744   *
745   * <p>This implementation is likely to be faster than {@code Double.parseDouble} if many failures
746   * are expected.
747   *
748   * @param string the string representation of a {@code double} value
749   * @return the floating point value represented by {@code string}, or {@code null} if {@code
750   *     string} has a length of zero or cannot be parsed as a {@code double} value
751   * @throws NullPointerException if {@code string} is {@code null}
752   * @since 14.0
753   */
754  @J2ktIncompatible
755  @GwtIncompatible // regular expressions
756  @CheckForNull
757  public static Double tryParse(String string) {
758    if (FLOATING_POINT_PATTERN.matcher(string).matches()) {
759      // TODO(lowasser): could be potentially optimized, but only with
760      // extensive testing
761      try {
762        return Double.parseDouble(string);
763      } catch (NumberFormatException e) {
764        // Double.parseDouble has changed specs several times, so fall through
765        // gracefully
766      }
767    }
768    return null;
769  }
770}