# SparseArray¶

class SparseArray

This class records a set of integers, where each integer is either present or not present in the set.

It is similar in principle and in interface to a BitArray (which can be thought of as a set of integers, one integer corresponding to each different bit position), but the SparseArray is implemented as a list of min/max subrange lists, rather than as a bitmask.

This makes it particularly efficient for storing sets which consist of large sections of consecutively included or consecutively excluded elements, with arbitrarily large integers, but particularly inefficient for doing boolean operations such as & or |.

Also, unlike BitArray, the SparseArray can store negative integers.

Inheritance diagram

SparseArray(void)
SparseArray(BitArray const &from)
SparseArray(SparseArray const&) = default
SparseArray all_off(void)

Returns a SparseArray whose bits are all off.

SparseArray all_on(void)

Returns a SparseArray with an infinite array of bits, all on.

SparseArray bit(int index)

Returns a SparseArray with only the indicated bit on.

void clear(void)

Sets all the bits in the SparseArray off.

void clear_bit(int index)

Sets the nth bit off. If n >= get_num_bits(), this automatically extends the array.

void clear_range(int low_bit, int size)

Sets the indicated range of bits off.

int compare_to(SparseArray const &other) const

Returns a number less than zero if this SparseArray sorts before the indicated other SparseArray, greater than zero if it sorts after, or 0 if they are equivalent. This is based on the same ordering defined by operator <.

bool get_bit(int index) const

Returns true if the nth bit is set, false if it is cleared. It is valid for n to increase beyond get_num_bits(), but the return value get_num_bits() will always be the same.

static TypeHandle get_class_type(void)
bool get_highest_bits(void) const

Returns true if the infinite set of bits beyond get_num_bits() are all on, or false of they are all off.

int get_highest_off_bit(void) const

Returns the index of the highest 0 bit in the array. Returns -1 if there are no 0 bits or if there an infinite number of 1 bits.

int get_highest_on_bit(void) const

Returns the index of the highest 1 bit in the array. Returns -1 if there are no 1 bits or if there an infinite number of 1 bits.

int get_lowest_off_bit(void) const

Returns the index of the lowest 0 bit in the array. Returns -1 if there are no 0 bits or if there are an infinite number of 1 bits.

int get_lowest_on_bit(void) const

Returns the index of the lowest 1 bit in the array. Returns -1 if there are no 1 bits or if there are an infinite number of 1 bits.

int get_max_num_bits(void)

If get_max_num_bits() returned true, this method may be called to return the maximum number of bits that may be stored in this structure. It is an error to call this if get_max_num_bits() return false.

It is always an error to call this method. The SparseArray has no maximum number of bits. This method is defined so generic programming algorithms can use BitMask or SparseArray interchangeably.

int get_next_higher_different_bit(int low_bit) const

Returns the index of the next bit in the array, above low_bit, whose value is different that the value of low_bit. Returns low_bit again if all bits higher than low_bit have the same value.

This can be used to quickly iterate through all of the bits in the array.

int get_num_bits(void) const

Returns the current number of possibly different bits in this array. There are actually an infinite number of bits, but every bit higher than this bit will have the same value, either 0 or 1 (see get_highest_bits()).

This number may grow and/or shrink automatically as needed.

int get_num_off_bits(void) const

Returns the number of bits that are set to 0 in the array. Returns -1 if there are an infinite number of 0 bits.

int get_num_on_bits(void) const

Returns the number of bits that are set to 1 in the array. Returns -1 if there are an infinite number of 1 bits.

std::size_t get_num_subranges(void) const

Returns the number of separate subranges stored in the SparseArray. You can use this limit to iterate through the subranges, calling get_subrange_begin() and get_subrange_end() for each one.

Also see is_inverse().

int get_subrange_begin(std::size_t n) const

Returns the first numeric element in the nth subrange.

Also see is_inverse().

int get_subrange_end(std::size_t n) const

Returns the last numeric element, plus one, in the nth subrange.

Also see is_inverse().

bool has_all_of(int low_bit, int size) const

Returns true if all bits in the indicated range are set, false otherwise.

bool has_any_of(int low_bit, int size) const

Returns true if any bit in the indicated range is set, false otherwise.

bool has_bits_in_common(SparseArray const &other) const

Returns true if this SparseArray has any “one” bits in common with the other one, false otherwise.

This is equivalent to (array & other) != 0, but may be faster.

bool has_max_num_bits(void)

Returns true if there is a maximum number of bits that may be stored in this structure, false otherwise. If this returns true, the number may be queried in get_max_num_bits().

This method always returns false. The SparseArray has no maximum number of bits. This method is defined so generic programming algorithms can use BitMask or SparseArray interchangeably.

void invert_in_place(void)

Inverts all the bits in the SparseArray. This is equivalent to array = ~array.

bool is_all_on(void) const

Returns true if the entire bitmask is one, false otherwise.

bool is_inverse(void) const

If this is true, the SparseArray is actually defined as a list of subranges of integers that are not in the set. If this is false (the default), then the subranges define the integers that are in the set. This affects the interpretation of the values returned by iterating through get_num_subranges().

bool is_zero(void) const

Returns true if the entire bitmask is zero, false otherwise.

SparseArray lower_on(int on_bits)

Returns a SparseArray whose lower on_bits bits are on.

void output(std::ostream &out) const
SparseArray range(int low_bit, int size)

Returns a SparseArray whose size bits, beginning at low_bit, are on.

void set_bit(int index)

Sets the nth bit on. If n >= get_num_bits(), this automatically extends the array.

void set_bit_to(int index, bool value)

Sets the nth bit either on or off, according to the indicated bool value.

void set_range(int low_bit, int size)

Sets the indicated range of bits on.

void set_range_to(bool value, int low_bit, int size)

Sets the indicated range of bits to either on or off.