# Class VectorMask<E>

java.lang.Object
jdk.incubator.vector.VectorMask<E>

Type Parameters:
  `E` - the boxed version of `ETYPE`, the element type of a vector

public abstract class VectorMask<E> extends Object
A `VectorMask` represents an ordered immutable sequence of `boolean` values.

A `VectorMask` and `Vector` of the same element type (`ETYPE`) and `shape` have the same number of lanes, and are therefore compatible (specifically, their `vector species` are compatible).

Some vector operations accept (compatible) masks to control the selection and operation of lane elements of input vectors.

The number of values in the sequence is referred to as the `VectorMask` `length`. The length also corresponds to the number of VectorMask lanes. The lane element at lane index `N` (from `0`, inclusive, to length, exclusive) corresponds to the `N + 1`'th value in the sequence.

A lane is said to be set if the lane element is `true`, otherwise a lane is said to be unset if the lane element is `false`.

VectorMask declares a limited set of unary, binary and reduction operations.

- A lane-wise unary operation operates on one input mask and produces a result mask. For each lane of the input mask the lane element is operated on using the specified scalar unary operation and the boolean result is placed into the mask result at the same lane. The following pseudocode illustrates the behavior of this operation category:

      VectorMask<E> a = ...;
      boolean[] ar = new boolean[a.length()];
      for (int i = 0; i < a.length(); i++) {
          ar[i] = scalar_unary_op(a.laneIsSet(i));
      }
      VectorMask<E> r = VectorMask.fromArray(a.vectorSpecies(), ar, 0);

- A lane-wise binary operation operates on two input masks to produce a result mask. For each lane of the two input masks a and b, the corresponding lane elements from a and b are operated on using the specified scalar binary operation and the boolean result is placed into the mask result at the same lane. The following pseudocode illustrates the behavior of this operation category:

      VectorMask<E> a = ...;
      VectorMask<E> b = ...;
      boolean[] ar = new boolean[a.length()];
      for (int i = 0; i < a.length(); i++) {
          ar[i] = scalar_binary_op(a.laneIsSet(i), b.laneIsSet(i));
      }
      VectorMask<E> r = VectorMask.fromArray(a.vectorSpecies(), ar, 0);

- A cross-lane reduction operation accepts an input mask and produces a scalar result. For each lane of the input mask the lane element is operated on, together with a scalar accumulation value, using the specified scalar binary operation. The scalar result is the final value of the accumulator. The following pseudocode illustrates the behaviour of this operation category:

      Mask<E> a = ...;
      int acc = zero_for_scalar_binary_op;  // 0, or 1 for &
      for (int i = 0; i < a.length(); i++) {
           acc = scalar_binary_op(acc, a.laneIsSet(i) ? 1 : 0);  // & | +
      }
      return acc;  // maybe boolean (acc != 0)

## Value-based classes and identity operations

`VectorMask`, along with `Vector`, is a value-based class. With `VectorMask`, identity-sensitive operations such as `==` may yield unpredictable results, or reduced performance. Oddly enough, `v.equals(w)` is likely to be faster than `v==w`, since `equals` is not an identity sensitive method. (Neither is `toString` nor `hashCode`.) Also, vector mask objects can be stored in locals and parameters and as `static final` constants, but storing them in other Java fields or in array elements, while semantically valid, may incur performance penalties.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract boolean`
  `allTrue()`
  Returns `true` if all the mask lanes are set.
  `abstract VectorMask<E>`
  `and(VectorMask<E> m)`
  Computes the logical intersection (as `a&b`) between this mask and a second input mask.
  `abstract VectorMask<E>`
  `andNot(VectorMask<E> m)`
  Logically subtracts a second input mask from this mask (as `a&~b`).
  `abstract boolean`
  `anyTrue()`
  Returns `true` if any of the mask lanes are set.
  `abstract <F> VectorMask<F>`
  `cast(VectorSpecies<F> species)`
  Converts this mask to a mask of the given species of element type `F`.
  `abstract <F> VectorMask<F>`
  `check(Class<F> elementType)`
  Checks that this mask applies to vectors with the given element type, and returns this mask unchanged.
  `abstract <F> VectorMask<F>`
  `check(VectorSpecies<F> species)`
  Checks that this mask has the given species, and returns this mask unchanged.
  `abstract VectorMask<E>`
  `compress()`
  Compresses set lanes from this mask.
  `abstract VectorMask<E>`
  `eq(VectorMask<E> m)`
  Determines logical equivalence of this mask to a second input mask (as boolean `a==b` or `a^~b`).
  `final boolean`
  `equals(Object obj)`
  Indicates whether this mask is identical to some other object.
  `abstract int`
  `firstTrue()`
  Returns the index of the first mask lane that is set.
  `static <E> VectorMask<E>`
  `fromArray(VectorSpecies<E> species, boolean[] bits, int offset)`
  Loads a mask from a `boolean` array starting at an offset.
  `static <E> VectorMask<E>`
  `fromLong(VectorSpecies<E> species, long bits)`
  Returns a mask where each lane is set or unset according to the bits in the given bitmask, starting with the least significant bit, and continuing up to the sign bit.
  `static <E> VectorMask<E>`
  `fromValues(VectorSpecies<E> species, boolean... bits)`
  Returns a mask where each lane is set or unset according to given `boolean` values.
  `protected final Object`
  `getPayload()`
  `final int`
  `hashCode()`
  Returns a hash code value for the mask, based on the mask bit settings and the vector species.
  `abstract VectorMask<E>`
  `indexInRange(int offset, int limit)`
  Removes lanes numbered `N` from this mask where the adjusted index `N+offset`, is not in the range `[0..limit-1]`.
  `abstract VectorMask<E>`
  `indexInRange(long offset, long limit)`
  Removes lanes numbered `N` from this mask where the adjusted index `N+offset`, is not in the range `[0..limit-1]`.
  `abstract void`
  `intoArray(boolean[] a, int offset)`
  Stores this mask into a `boolean` array starting at offset.
  `abstract boolean`
  `laneIsSet(int i)`
  Tests if the lane at index `i` is set
  `abstract int`
  `lastTrue()`
  Returns the index of the last mask lane that is set.
  `final int`
  `length()`
  Returns the number of mask lanes.
  `abstract VectorMask<E>`
  `not()`
  Logically negates this mask.
  `abstract VectorMask<E>`
  `or(VectorMask<E> m)`
  Computes the logical union (as `a|b`) of this mask and a second input mask.
  `abstract boolean[]`
  `toArray()`
  Returns an `boolean` array containing the lane elements of this mask.
  `abstract long`
  `toLong()`
  Returns the lane elements of this mask packed into a `long` value for at most the first 64 lane elements.
  `final String`
  `toString()`
  Returns a string representation of this mask, of the form `"Mask[T.TT...]"`, reporting the mask bit settings (as 'T' or '.' characters) in lane order.
  `abstract Vector<E>`
  `toVector()`
  Returns a vector representation of this mask, the lane bits of which are set or unset in correspondence to the mask bits.
  `abstract int`
  `trueCount()`
  Returns the number of mask lanes that are set.
  `abstract VectorSpecies<E>`
  `vectorSpecies()`
  Returns the vector species to which this mask applies.
  `abstract VectorMask<E>`
  `xor(VectorMask<E> m)`
  Determines logical symmetric difference (as `a^b`) of this mask and a second input mask.

  ### Methods declared in class Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`
  Modifier and Type
  Method
  Description
  `protected Object`
  `clone()`
  Creates and returns a copy of this object.
  `protected void`
  `finalize()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  Finalization is deprecated and subject to removal in a future release.
  `final Class<?>`
  `getClass()`
  Returns the runtime class of this `Object`.
  `final void`
  `notify()`
  Wakes up a single thread that is waiting on this object's monitor.
  `final void`
  `notifyAll()`
  Wakes up all threads that are waiting on this object's monitor.
  `final void`
  `wait()`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
  `final void`
  `wait(long timeoutMillis)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
  `final void`
  `wait(long timeoutMillis, int nanos)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

- ## Method Details

  - ### vectorSpecies

    public abstract VectorSpecies<E> vectorSpecies()
    Returns the vector species to which this mask applies. This mask applies to vectors of the same species, and the same number of lanes.
    Returns:
      the vector species of this mask

  - ### length

    public final int length()
    Returns the number of mask lanes. This mask applies to vectors of the same number of lanes, and the same species.
    Returns:
      the number of mask lanes

  - ### fromValues

    public static <E> VectorMask<E> fromValues(VectorSpecies<E> species, boolean... bits)
    Returns a mask where each lane is set or unset according to given `boolean` values.

    For each mask lane, where `N` is the mask lane index, if the given `boolean` value at index `N` is `true` then the mask lane at index `N` is set, otherwise it is unset.

    The given species must have a number of lanes that is compatible with the given array.

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - vector species for the desired mask
      `bits` - the given `boolean` values
    Returns:
      a mask where each lane is set or unset according to the given `boolean` value
    Throws:
      `IllegalArgumentException` - if `bits.length != species.length()`
    See Also:
      - `fromLong(VectorSpecies, long)`
      - `fromArray(VectorSpecies, boolean[], int)`

  - ### fromArray

    public static <E> VectorMask<E> fromArray(VectorSpecies<E> species, boolean[] bits, int offset)
    Loads a mask from a `boolean` array starting at an offset.

    For each mask lane, where `N` is the mask lane index, if the array element at index `offset + N` is `true` then the mask lane at index `N` is set, otherwise it is unset.

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - vector species for the desired mask
      `bits` - the `boolean` array
      `offset` - the offset into the array
    Returns:
      the mask loaded from the `boolean` array
    Throws:
      `IndexOutOfBoundsException` - if `offset < 0`, or `offset > bits.length - species.length()`
    See Also:
      - `fromLong(VectorSpecies, long)`
      - `fromValues(VectorSpecies, boolean...)`

  - ### fromLong

    public static <E> VectorMask<E> fromLong(VectorSpecies<E> species, long bits)
    Returns a mask where each lane is set or unset according to the bits in the given bitmask, starting with the least significant bit, and continuing up to the sign bit.

    For each mask lane, where `N` is the mask lane index, if the expression `(bits>>min(63,N))&1` is non-zero, then the mask lane at index `N` is set, otherwise it is unset.

    If the given species has fewer than 64 lanes, the high `64-VLENGTH` bits of the bit-mask are ignored. If the given species has more than 64 lanes, the sign bit is replicated into lane 64 and beyond.

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - vector species for the desired mask
      `bits` - the given mask bits, as a 64-bit signed integer
    Returns:
      a mask where each lane is set or unset according to the bits in the given integer value
    See Also:
      - `fromValues(VectorSpecies, boolean...)`
      - `fromArray(VectorSpecies, boolean[], int)`

  - ### cast

    public abstract <F> VectorMask<F> cast(VectorSpecies<F> species)
    Converts this mask to a mask of the given species of element type `F`. The `species.length()` must be equal to the mask length. The various mask lane bits are unmodified.

    For each mask lane, where `N` is the lane index, if the mask lane at index `N` is set, then the mask lane at index `N` of the resulting mask is set, otherwise that mask lane is not set.

    Type Parameters:
      `F` - the boxed element type of the species
    Parameters:
      `species` - vector species for the desired mask
    Returns:
      a mask converted by shape and element type
    Throws:
      `IllegalArgumentException` - if this mask length and the species length differ

  - ### toLong

    public abstract long toLong()
    Returns the lane elements of this mask packed into a `long` value for at most the first 64 lane elements.

    The lane elements are packed in the order of least significant bit to most significant bit. For each mask lane where `N` is the mask lane index, if the mask lane is set then the `N`th bit is set to one in the resulting `long` value, otherwise the `N`th bit is set to zero. The mask must have no more than 64 lanes.

    Returns:
      the lane elements of this mask packed into a `long` value.
    Throws:
      `UnsupportedOperationException` - if there are more than 64 lanes in this mask

  - ### toArray

    public abstract boolean[] toArray()
    Returns an `boolean` array containing the lane elements of this mask.

    This method behaves as if it stores this mask into an allocated array (using `intoArray(boolean[], int)`) and returns that array as follows:

        boolean[] a = new boolean[this.length()];
        this.intoArray(a, 0);
        return a;

    Returns:
      an array containing the lane elements of this vector

  - ### intoArray

    public abstract void intoArray(boolean[] a, int offset)
    Stores this mask into a `boolean` array starting at offset.

    For each mask lane, where `N` is the mask lane index, the lane element at index `N` is stored into the array element `a[offset+N]`.

    Parameters:
      `a` - the array, of type boolean[]
      `offset` - the offset into the array
    Throws:
      `IndexOutOfBoundsException` - if `offset < 0` or `offset > a.length - this.length()`

  - ### anyTrue

    public abstract boolean anyTrue()
    Returns `true` if any of the mask lanes are set.
    Returns:
      `true` if any of the mask lanes are set, otherwise `false`.

  - ### allTrue

    public abstract boolean allTrue()
    Returns `true` if all the mask lanes are set.
    Returns:
      `true` if all the mask lanes are set, otherwise `false`.

  - ### trueCount

    public abstract int trueCount()
    Returns the number of mask lanes that are set.
    Returns:
      the number of mask lanes that are set.

  - ### firstTrue

    public abstract int firstTrue()
    Returns the index of the first mask lane that is set. Returns `VLENGTH` if none of them are set.
    Returns:
      the index of the first mask lane that is set, or `VLENGTH`

  - ### lastTrue

    public abstract int lastTrue()
    Returns the index of the last mask lane that is set. Returns `-1` if none of them are set.
    Returns:
      the index of the last mask lane that is set, or `-1`

  - ### and

    public abstract VectorMask<E> and(VectorMask<E> m)
    Computes the logical intersection (as `a&b`) between this mask and a second input mask.

    This is a lane-wise binary operation which applies the logical `AND` operation (`&`) to each corresponding pair of mask bits.

    Parameters:
      `m` - the second input mask
    Returns:
      the result of logically conjoining the two input masks

  - ### or

    public abstract VectorMask<E> or(VectorMask<E> m)
    Computes the logical union (as `a|b`) of this mask and a second input mask.

    This is a lane-wise binary operation which applies the logical `OR` operation (`|`) to each corresponding pair of mask bits.

    Parameters:
      `m` - the input mask
    Returns:
      the result of logically disjoining the two input masks

  - ### xor

    public abstract VectorMask<E> xor(VectorMask<E> m)
    Determines logical symmetric difference (as `a^b`) of this mask and a second input mask.

    This is a lane-wise binary operation which applies the logical `XOR` operation (`^`) to each corresponding pair of mask bits.

    Parameters:
      `m` - the input mask
    Returns:
      the result of logically disjunctively disjoining the two input masks

  - ### andNot

    public abstract VectorMask<E> andNot(VectorMask<E> m)
    Logically subtracts a second input mask from this mask (as `a&~b`).

    This is a lane-wise binary operation which applies the logical `ANDC` operation (`&~`) to each corresponding pair of mask bits.

    Parameters:
      `m` - the second input mask
    Returns:
      the result of logically subtracting the second mask from this mask

  - ### eq

    public abstract VectorMask<E> eq(VectorMask<E> m)
    Determines logical equivalence of this mask to a second input mask (as boolean `a==b` or `a^~b`).

    This is a lane-wise binary operation tests each corresponding pair of mask bits for equality. It is also equivalent to the logical `XNOR` operation (`^~`) to each corresponding pair of mask bits.

    Parameters:
      `m` - the input mask
    Returns:
      a mask showing where the two input masks were equal
    See Also:
      - `equals(Object)`

  - ### not

    public abstract VectorMask<E> not()
    Logically negates this mask.

    This is a lane-wise binary operation which applies the logical `NOT` operation (`~`) to each mask bit.

    Returns:
      the result of logically negating this mask

  - ### indexInRange

    public abstract VectorMask<E> indexInRange(int offset, int limit)
    Removes lanes numbered `N` from this mask where the adjusted index `N+offset`, is not in the range `[0..limit-1]`.

    In all cases the series of set and unset lanes is assigned as if by using infinite precision or `VLENGTH-`saturating additions or subtractions, without overflow or wrap-around.

    API Note:
      This method performs a SIMD emulation of the check performed by `Objects.checkIndex(int,int)`, on the index numbers in the range `[offset..offset+VLENGTH-1]`. If an exception is desired, the resulting mask can be compared with the original mask; if they are not equal, then at least one lane was out of range, and exception processing can be performed.

      A mask which is a series of `N` set lanes followed by a series of unset lanes can be obtained by calling `allTrue.indexInRange(0, N)`, where `allTrue` is a mask of all true bits. A mask of `N1` unset lanes followed by `N2` set lanes can be obtained by calling `allTrue.indexInRange(-N1, N2)`.

    Parameters:
      `offset` - the starting index
      `limit` - the upper-bound (exclusive) of index range
    Returns:
      the original mask, with out-of-range lanes unset
    See Also:
      - `VectorSpecies.indexInRange(int, int)`

  - ### indexInRange

    public abstract VectorMask<E> indexInRange(long offset, long limit)
    Removes lanes numbered `N` from this mask where the adjusted index `N+offset`, is not in the range `[0..limit-1]`.

    In all cases the series of set and unset lanes is assigned as if by using infinite precision or `VLENGTH-`saturating additions or subtractions, without overflow or wrap-around.

    API Note:
      This method performs a SIMD emulation of the check performed by `Objects.checkIndex(long,long)`, on the index numbers in the range `[offset..offset+VLENGTH-1]`. If an exception is desired, the resulting mask can be compared with the original mask; if they are not equal, then at least one lane was out of range, and exception processing can be performed.

      A mask which is a series of `N` set lanes followed by a series of unset lanes can be obtained by calling `allTrue.indexInRange(0, N)`, where `allTrue` is a mask of all true bits. A mask of `N1` unset lanes followed by `N2` set lanes can be obtained by calling `allTrue.indexInRange(-N1, N2)`.

    Parameters:
      `offset` - the starting index
      `limit` - the upper-bound (exclusive) of index range
    Returns:
      the original mask, with out-of-range lanes unset
    Since:
      19
    See Also:
      - `VectorSpecies.indexInRange(long, long)`

  - ### toVector

    public abstract Vector<E> toVector()
    Returns a vector representation of this mask, the lane bits of which are set or unset in correspondence to the mask bits. For each mask lane, where `N` is the mask lane index, if the mask lane is set at `N` then the specific non-default value `-1` is placed into the resulting vector at lane index `N`. Otherwise, the default element value `0` is placed into the resulting vector at lane index `N`. Whether the element type (`ETYPE`) of this mask is floating point or integral, the lane value, as selected by the mask, will be one of the two arithmetic values `0` or `-1`. For every `ETYPE` the most significant bit of the vector lane is set if and only if the mask lane is set. In addition, for integral types, all lane bits are set in lanes where the mask is set.

    The vector returned is the same as would be computed by `ZERO.blend(MINUS_ONE, this)`, where `ZERO` and `MINUS_ONE` are vectors which replicate the default `ETYPE` value and the `ETYPE` value representing `-1`, respectively.

    API Note:
      For the sake of static type checking, users may wish to check the resulting vector against the expected integral lane type or species. If the mask is for a float-point species, then the resulting vector will have the same shape and lane size, but an integral type. If the mask is for an integral species, the resulting vector will be of exactly that species.
    Returns:
      a vector representation of this mask
    See Also:
      - `Vector.check(Class)`
      - `Vector.check(VectorSpecies)`

  - ### laneIsSet

    public abstract boolean laneIsSet(int i)
    Tests if the lane at index `i` is set
    Parameters:
      `i` - the lane index
    Returns:
      true if the lane at index `i` is set, otherwise false
    Throws:
      `IndexOutOfBoundsException` - if the index is out of range (`< 0 || >= length()`)

  - ### check

    public abstract <F> VectorMask<F> check(Class<F> elementType)
    Checks that this mask applies to vectors with the given element type, and returns this mask unchanged. The effect is similar to this pseudocode: `elementType == vectorSpecies().elementType() ? this : throw new ClassCastException()`.
    Type Parameters:
      `F` - the boxed element type of the required lane type
    Parameters:
      `elementType` - the required lane type
    Returns:
      the same mask
    Throws:
      `ClassCastException` - if the element type is wrong
    See Also:
      - `Vector.check(Class)`
      - `check(VectorSpecies)`

  - ### check

    public abstract <F> VectorMask<F> check(VectorSpecies<F> species)
    Checks that this mask has the given species, and returns this mask unchanged. The effect is similar to this pseudocode: `species == vectorSpecies() ? this : throw new ClassCastException()`.
    Type Parameters:
      `F` - the boxed element type of the required species
    Parameters:
      `species` - vector species required for this mask
    Returns:
      the same mask
    Throws:
      `ClassCastException` - if the species is wrong
    See Also:
      - `Vector.check(Class)`
      - `Vector.check(VectorSpecies)`

  - ### toString

    public final String toString()
    Returns a string representation of this mask, of the form `"Mask[T.TT...]"`, reporting the mask bit settings (as 'T' or '.' characters) in lane order.
    Overrides:
      `toString` in class `Object`
    Returns:
      a string of the form `"Mask[T.TT...]"`

  - ### equals

    public final boolean equals(Object obj)
    Indicates whether this mask is identical to some other object. Two masks are identical only if they have the same species and same source indexes, in the same order.
    Overrides:
      `equals` in class `Object`
    Parameters:
      `obj` - the reference object with which to compare.
    Returns:
      whether this vector is identical to some other object
    See Also:
      - `eq(VectorMask)`

  - ### hashCode

    public final int hashCode()
    Returns a hash code value for the mask, based on the mask bit settings and the vector species.
    Overrides:
      `hashCode` in class `Object`
    Returns:
      a hash code value for this mask
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(Object)`

  - ### compress

    public abstract VectorMask<E> compress()
    Compresses set lanes from this mask. Returns a mask which is a series of `N` set lanes followed by a series of unset lanes, where `N` is the true count of this mask.
    Returns:
      the compressed mask of this mask
    Since:
      19

  - ### getPayload

    protected final Object getPayload()