Module jdk.incubator.vector
Package jdk.incubator.vector

# Class VectorShuffle<E>

java.lang.Object
jdk.internal.vm.vector.VectorSupport.VectorPayload
jdk.internal.vm.vector.VectorSupport.VectorShuffle<E>
jdk.incubator.vector.VectorShuffle<E>

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

public abstract class VectorShuffle<E> extends jdk.internal.vm.vector.VectorSupport.VectorShuffle<E>
A `VectorShuffle` represents an ordered immutable sequence of `int` values called source indexes, where each source index numerically selects a source lane from a compatible `Vector`.

A `VectorShuffle` 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).

A shuffle is applied to a (compatible) source vector with the `rearrange` method.

A shuffle has a lane structure derived from its vector species, but it stores lane indexes, as `int`s, rather than lane values.

This method gathers lane values by random access to the source vector, selecting lanes by consulting the source indexes. If a source index appears more than once in a shuffle, then the selected lane's value is copied more than once into the result. If a particular lane is never selected by a source index, that lane's value is ignored. The resulting vector contains all the source lane values selected by the source indexes of the shuffle. The resulting lane values are ordered according to the shuffle's source indexes, not according to the original vector's lane order.

Each shuffle has a `vectorSpecies()` property which determines the compatibility of vectors the shuffle operates on. This ensures that the `length()` of a shuffle is always equal to the VLENGTH of any vector it operates on. The element type and shape of the shuffle's species are not directly relevant to the behavior of the shuffle. Shuffles can easily be converted to other lane types, as long as the lane count stays constant.

In its internal state, a shuffle always holds integral values in a narrow range from `[-VLENGTH..VLENGTH-1]`. The positive numbers are self-explanatory; they are lane numbers applied to any source vector. The negative numbers, when present, are a sign that the shuffle was created from a raw integer value which was not a valid lane index.

An invalid source index, represented in a shuffle by a negative number, is called an exceptional index.

Exceptional indexes are processed in a variety of ways:

- Unless documented otherwise, shuffle-using methods will throw `ArrayIndexOutOfBoundsException` when a lane is processed by an exceptional index.
- When an invalid source index (negative or not) is first loaded into a shuffle, it is partially normalized to the negative range of `[-VLENGTH..-1]` as if by `wrapIndex()`. This treatment of exceptional indexes is called partial wrapping, because it preserves the distinction between normal and exceptional indexes, while wrapping them into adjacent ranges of positive and non-positive numbers. A partially wrapped index can later on be fully wrapped into the positive range by adding a final offset of `VLENGTH`.
- In some applications, exceptional indexes used to "steer" access to a second source vector. In those cases, the exception index values, which are in the range `[-VLENGTH..-1]`, are cycled up to the valid range `[0..VLENGTH-1]` and used on the second source vector.
- When a shuffle is cast from another shuffle species with a smaller `VLENGTH`, all indexes are re-validated against the new `VLENGTH`, and some may be converted to exceptional indexes. In any case, shuffle casting never converts exceptional indexes to normal ones.

## Value-based classes and identity operations

`VectorShuffle`, along with `Vector` is a value-based class. Identity-sensitive operations such as `==` may yield unpredictable results, or reduced performance. Also, vector shuffle 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. Finally, vector shuffles should not be computed in loops, when possible, but instead should be stored in loop-invariant locals or as `static final` constants.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract <F> VectorShuffle<F>`
  `cast​(VectorSpecies<F> species)`
  Converts this shuffle to a shuffle of the given species of element type `F`.
  `abstract <F> VectorShuffle<F>`
  `check​(VectorSpecies<F> species)`
  Checks that this shuffle has the given species, and returns this shuffle unchanged.
  `abstract int`
  `checkIndex​(int index)`
  Validation function for lane indexes which may be out of the valid range of `[0..VLENGTH-1]`.
  `abstract VectorShuffle<E>`
  `checkIndexes()`
  Apply the `checkIndex()` validation function to all lanes, throwing `IndexOutOfBoundsException` if there are any exceptional indexes in this shuffle.
  `boolean`
  `equals​(Object obj)`
  Indicates whether this shuffle is identical to some other object.
  `static <E> VectorShuffle<E>`
  `fromArray​(VectorSpecies<E> species, int[] sourceIndexes, int offset)`
  Creates a shuffle for a given species from an `int` array starting at an offset.
  `static <E> VectorShuffle<E>`
  `fromOp​(VectorSpecies<E> species, IntUnaryOperator fn)`
  Creates a shuffle for a given species from the successive values of an operator applied to the range `[0..VLENGTH-1]`.
  `static <E> VectorShuffle<E>`
  `fromValues​(VectorSpecies<E> species, int... sourceIndexes)`
  Creates a shuffle for a given species from a series of source indexes.
  `int`
  `hashCode()`
  Returns a hash code value for the shuffle, based on the lane source indexes and the vector species.
  `abstract void`
  `intoArray​(int[] a, int offset)`
  Stores this shuffle into an `int` array starting at offset.
  `static <E> VectorShuffle<E>`
  `iota​(VectorSpecies<E> species, int start, int step, boolean wrap)`
  Creates a shuffle using source indexes set to sequential values starting from `start` and stepping by the given `step`.
  `abstract VectorMask<E>`
  `laneIsValid()`
  Find all lanes containing valid indexes (non-negative values) and return a mask where exactly those lanes are set.
  `int`
  `laneSource​(int i)`
  Gets the `int` lane element at lane index `i`
  `int`
  `length()`
  Returns the number of lanes processed by this shuffle.
  `static <E> VectorShuffle<E>`
  `makeUnzip​(VectorSpecies<E> species, int part)`
  Creates a shuffle which will unzip the concatenation of two vectors, alternatively storing input lanes into one or the other output vector.
  `static <E> VectorShuffle<E>`
  `makeZip​(VectorSpecies<E> species, int part)`
  Creates a shuffle which will zip together two vectors, alternatively selecting lanes from one or the other.
  `abstract VectorShuffle<E>`
  `rearrange​(VectorShuffle<E> s)`
  Rearranges the lane elements of this shuffle selecting lane indexes controlled by another shuffle.
  `abstract int[]`
  `toArray()`
  Returns an `int` array containing the lane source indexes of this shuffle.
  `String`
  `toString()`
  Returns a string representation of this shuffle, of the form `"Shuffle[0,1,2...]"`, reporting the source indexes in lane order.
  `abstract Vector<E>`
  `toVector()`
  Converts this shuffle into a vector, creating a vector of integral values corresponding to the lane source indexes of the shuffle.
  `abstract VectorSpecies<E>`
  `vectorSpecies()`
  Returns the species of this shuffle.
  `abstract int`
  `wrapIndex​(int index)`
  Validation function for lane indexes which may be out of the valid range of `[0..VLENGTH-1]`.
  `abstract VectorShuffle<E>`
  `wrapIndexes()`
  Apply the `wrapIndex()` validation function to all lanes, replacing any exceptional indexes with wrapped normal indexes.

  ### Methods declared in class jdk.internal.vm.vector.VectorSupport.VectorPayload

  `getPayload`

  ### Methods declared in class java.lang.Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- ## Method Details

  - ### vectorSpecies

    public abstract VectorSpecies<E> vectorSpecies()
    Returns the species of this shuffle.
    Returns:
      the species of this shuffle

  - ### length

    public final int length()
    Returns the number of lanes processed by this shuffle. This is the same as the `VLENGTH` of any vector it operates on.
    Returns:
      the number of shuffle lanes

  - ### cast

    public abstract <F> VectorShuffle<F> cast​(VectorSpecies<F> species)
    Converts this shuffle to a shuffle of the given species of element type `F`. The various lane source indexes are unmodified. Exceptional source indexes remain exceptional and valid indexes remain valid.
    Type Parameters:
      `F` - the boxed element type of the species
    Parameters:
      `species` - the species of desired shuffle
    Returns:
      a shuffle converted by shape and element type
    Throws:
      `IllegalArgumentException` - if this shuffle length and the species length differ

  - ### check

    public abstract <F> VectorShuffle<F> check​(VectorSpecies<F> species)
    Checks that this shuffle has the given species, and returns this shuffle 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` - the required species
    Returns:
      the same shuffle
    Throws:
      `ClassCastException` - if the shuffle species is wrong
    See Also:
      `Vector.check(Class)`, `Vector.check(VectorSpecies)`

  - ### checkIndex

    public abstract int checkIndex​(int index)
    Validation function for lane indexes which may be out of the valid range of `[0..VLENGTH-1]`. If `index` is in this range, it is returned unchanged. Otherwise, an `IndexOutOfBoundsException` is thrown.
    Parameters:
      `index` - the lane index
    Returns:
      `index`
    Throws:
      `IndexOutOfBoundsException` - if the `index` is not less than `VLENGTH`, or is negative
    See Also:
      `wrapIndex(int)`, `checkIndexes()`

  - ### wrapIndex

    public abstract int wrapIndex​(int index)
    Validation function for lane indexes which may be out of the valid range of `[0..VLENGTH-1]`. The `index` is forced into this range by adding or subtracting a suitable multiple of `VLENGTH`. Specifically, the index is reduced into the required range by computing the value of `length-floor`, where `floor=vectorSpecies().loopBound(length)` is the next lower multiple of `VLENGTH`. As long as `VLENGTH` is a power of two, then the reduced index also equal to `index & (VLENGTH - 1)`.
    Parameters:
      `index` - the lane index
    Returns:
      `index`, adjusted to the range `[0..VLENGTH-1`} by an appropriate multiple of `VLENGTH`
    See Also:
      `VectorSpecies.loopBound(int)`, `checkIndex(int)`, `wrapIndexes()`

  - ### checkIndexes

    public abstract VectorShuffle<E> checkIndexes()
    Apply the `checkIndex()` validation function to all lanes, throwing `IndexOutOfBoundsException` if there are any exceptional indexes in this shuffle.
    Returns:
      the current shuffle, unchanged
    Throws:
      `IndexOutOfBoundsException` - if any lanes in this shuffle contain exceptional indexes
    See Also:
      `checkIndex(int)`, `wrapIndexes()`

  - ### wrapIndexes

    public abstract VectorShuffle<E> wrapIndexes()
    Apply the `wrapIndex()` validation function to all lanes, replacing any exceptional indexes with wrapped normal indexes.
    Returns:
      the current shuffle, with all exceptional indexes wrapped
    See Also:
      `wrapIndex(int)`, `checkIndexes()`

  - ### laneIsValid

    public abstract VectorMask<E> laneIsValid()
    Find all lanes containing valid indexes (non-negative values) and return a mask where exactly those lanes are set.
    Returns:
      a mask of lanes containing valid source indexes
    See Also:
      `checkIndexes()`

  - ### fromValues

    public static <E> VectorShuffle<E> fromValues​(VectorSpecies<E> species, int... sourceIndexes)
    Creates a shuffle for a given species from a series of source indexes.

    For each shuffle lane, where `N` is the shuffle lane index, the `N`th index value is validated against the species `VLENGTH`, and (if invalid) is partially wrapped to an exceptional index in the range `[-VLENGTH..-1]`.

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - shuffle species
      `sourceIndexes` - the source indexes which the shuffle will draw from
    Returns:
      a shuffle where each lane's source index is set to the given `int` value, partially wrapped if exceptional
    Throws:
      `IndexOutOfBoundsException` - if `sourceIndexes.length != VLENGTH`
    See Also:
      `VectorSpecies.shuffleFromValues(int...)`

  - ### fromArray

    public static <E> VectorShuffle<E> fromArray​(VectorSpecies<E> species, int[] sourceIndexes, int offset)
    Creates a shuffle for a given species from an `int` array starting at an offset.

    For each shuffle lane, where `N` is the shuffle lane index, the array element at index `offset + N` is validated against the species `VLENGTH`, and (if invalid) is partially wrapped to an exceptional index in the range `[-VLENGTH..-1]`.

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - shuffle species
      `sourceIndexes` - the source indexes which the shuffle will draw from
      `offset` - the offset into the array
    Returns:
      a shuffle where each lane's source index is set to the given `int` value, partially wrapped if exceptional
    Throws:
      `IndexOutOfBoundsException` - if `offset < 0`, or `offset > sourceIndexes.length - VLENGTH`
    See Also:
      `VectorSpecies.shuffleFromArray(int[], int)`

  - ### fromOp

    public static <E> VectorShuffle<E> fromOp​(VectorSpecies<E> species, IntUnaryOperator fn)
    Creates a shuffle for a given species from the successive values of an operator applied to the range `[0..VLENGTH-1]`.

    For each shuffle lane, where `N` is the shuffle lane index, the `N`th index value is validated against the species `VLENGTH`, and (if invalid) is partially wrapped to an exceptional index in the range `[-VLENGTH..-1]`.

    Care should be taken to ensure `VectorShuffle` values produced from this method are consumed as constants to ensure optimal generation of code. For example, shuffle values can be held in `static final` fields or loop-invariant local variables.

    This method behaves as if a shuffle is created from an array of mapped indexes as follows:

           int[] a = new int[species.length()];
           for (int i = 0; i < a.length; i++) {
               a[i] = fn.applyAsInt(i);
           }
           return VectorShuffle.fromArray(a, 0);

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - shuffle species
      `fn` - the lane index mapping function
    Returns:
      a shuffle of mapped indexes
    See Also:
      `VectorSpecies.shuffleFromOp(IntUnaryOperator)`

  - ### iota

    public static <E> VectorShuffle<E> iota​(VectorSpecies<E> species, int start, int step, boolean wrap)
    Creates a shuffle using source indexes set to sequential values starting from `start` and stepping by the given `step`.

    This method returns the value of the expression `VectorShuffle.fromOp(species, i -> R(start + i * step))`, where `R` is `wrapIndex` if `wrap` is true, and is the identity function otherwise.

    If `wrap` is false each index is validated against the species `VLENGTH`, and (if invalid) is partially wrapped to an exceptional index in the range `[-VLENGTH..-1]`. Otherwise, if `wrap` is true, also reduce each index, as if by `wrapIndex`, to the valid range `[0..VLENGTH-1]`.

    API Note:
      The `wrap` parameter should be set to `true` if invalid source indexes should be wrapped. Otherwise, setting it to `false` allows invalid source indexes to be range-checked by later operations such as `unary rearrange`.
    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - shuffle species
      `start` - the starting value of the source index sequence
      `step` - the difference between adjacent source indexes
      `wrap` - whether to wrap resulting indexes
    Returns:
      a shuffle of sequential lane indexes, possibly wrapped
    See Also:
      `VectorSpecies.iotaShuffle(int,int,boolean)`

  - ### makeZip

    public static <E> VectorShuffle<E> makeZip​(VectorSpecies<E> species, int part)
    Creates a shuffle which will zip together two vectors, alternatively selecting lanes from one or the other. The logical result of a zip is twice the size of either input, and so the expanded result is broken into two physical parts, selected by a part number. For example, zipping two vectors `[a,b,c,d]` and `[1,2,3,4]` will yield the expanded logical result `[a,1,b,2,c,3,d,4]` which must be obtained in two parts, `[a,1,b,2]` and `[c,3,d,4]`.

    This method returns the value of the expression `VectorShuffle.fromOp(species, i -> i/2 + (i%2)*VLENGTH + P`, where `P` is `part*VLENGTH/2`.

    s Note that the source indexes in the odd lanes of the shuffle will be invalid indexes (`>= VLENGTH`, or `< 0` after partial normalization), which will select from the second vector.

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - the shuffle species
      `part` - the part number of the result (either zero or one)
    Returns:
      a shuffle which zips two vectors into `2*VLENGTH` lanes, returning the selected part
    Throws:
      `ArrayIndexOutOfBoundsException` - if `part` is not zero or one
    See Also:
      `makeUnzip(VectorSpecies, int)`, `Vector.rearrange(VectorShuffle,Vector)`

  - ### makeUnzip

    public static <E> VectorShuffle<E> makeUnzip​(VectorSpecies<E> species, int part)
    Creates a shuffle which will unzip the concatenation of two vectors, alternatively storing input lanes into one or the other output vector. Since the logical result of an unzip is twice the size of either input, the expanded result is broken into two physical parts, selected by a part number. For example, unzipping two vectors `[a,1,b,2][c,3,d,4]` will yield a result in two parts, `[a,b,c,d]` and `[1,2,3,4]`.

    This method returns the value of the expression `VectorShuffle.fromOp(species, i -> i*2+part`.

    Note that the source indexes in upper half of the shuffle will be invalid indexes (`>= VLENGTH`, or `< 0` after partial normalization), which will select from the second vector.

    Type Parameters:
      `E` - the boxed element type
    Parameters:
      `species` - the shuffle species
      `part` - the part number of the result (either zero or one)
    Returns:
      a shuffle which unzips `2*VLENGTH` lanes into two vectors, returning the selected part
    Throws:
      `ArrayIndexOutOfBoundsException` - if `part` is not zero or one
    See Also:
      `makeZip(VectorSpecies,int)`, `Vector.rearrange(VectorShuffle,Vector)`

  - ### toArray

    public abstract int[] toArray()
    Returns an `int` array containing the lane source indexes of this shuffle.

    This method behaves as if it stores this shuffle into an allocated array (using `intoArray`) and returns that array as follows:

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

    API Note:
      Shuffle source indexes are always in the range from `-VLENGTH` to `VLENGTH-1`. A source index is exceptional if and only if it is negative.
    Returns:
      an array containing the lane source indexes of this shuffle

  - ### intoArray

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

    For each shuffle lane `N`, the lane source index stored for that lane element is stored into the array element `a[offset+N]`.

    API Note:
      Shuffle source indexes are always in the range from `-VLENGTH` to `VLENGTH-1`.
    Parameters:
      `a` - the array, of type `int[]`
      `offset` - the offset into the array
    Throws:
      `IndexOutOfBoundsException` - if `offset < 0` or `offset > a.length - this.length()`

  - ### toVector

    public abstract Vector<E> toVector()
    Converts this shuffle into a vector, creating a vector of integral values corresponding to the lane source indexes of the shuffle.

    This method behaves as if it returns the result of creating a vector given an `int` array obtained from this shuffle's lane elements, as follows:

           int[] sa = this.toArray();
           $type$[] va = new $type$[a.length];
           for (int i = 0; i < a.length; i++) {
               va[i] = ($type$) sa[i];
           }
           return IntVector.fromArray(va, 0);

    API Note:
      Shuffle source indexes are always in the range from `-VLENGTH` to `VLENGTH-1`. These values are converted to the `ETYPE` of the resulting vector, even if it is a floating point type.
    Returns:
      a vector representation of this shuffle

  - ### laneSource

    public int laneSource​(int i)
    Gets the `int` lane element at lane index `i`
    Parameters:
      `i` - the lane index
    Returns:
      the `int` lane element at lane index `i`

  - ### rearrange

    public abstract VectorShuffle<E> rearrange​(VectorShuffle<E> s)
    Rearranges the lane elements of this shuffle selecting lane indexes controlled by another shuffle.

    For each lane of the specified shuffle, at lane index `N` with lane element `I`, the lane element at `I` from this shuffle is selected and placed into the resulting shuffle at `N`.

    Parameters:
      `s` - the shuffle controlling lane index selection
    Returns:
      the rearrangement of the lane elements of this shuffle

  - ### toString

    public final String toString()
    Returns a string representation of this shuffle, of the form `"Shuffle[0,1,2...]"`, reporting the source indexes in lane order.
    Overrides:
      `toString` in class `Object`
    Returns:
      a string of the form `"Shuffle[0,1,2...]"`

  - ### equals

    public final boolean equals​(Object obj)
    Indicates whether this shuffle is identical to some other object. Two shuffles 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:
      `Object.hashCode()`, `HashMap`

  - ### hashCode

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