/
bit_array.cr
451 lines (402 loc) · 12.8 KB
/
bit_array.cr
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# `BitArray` is an array data structure that compactly stores bits.
#
# Bits externally represented as `Bool`s are stored internally as
# `UInt32`s. The total number of bits stored is set at creation and is
# immutable.
#
# ### Example
#
# ```
# require "bit_array"
#
# ba = BitArray.new(12) # => "BitArray[000000000000]"
# ba[2] # => false
# 0.upto(5) { |i| ba[i * 2] = true }
# ba # => "BitArray[101010101010]"
# ba[2] # => true
# ```
struct BitArray
include Indexable::Mutable(Bool)
# The number of bits the BitArray stores
getter size : Int32
# Creates a new `BitArray` of *size* bits.
#
# *initial* optionally sets the starting value, `true` or `false`, for all bits
# in the array.
def initialize(@size, initial : Bool = false)
value = initial ? UInt32::MAX : UInt32::MIN
@bits = Pointer(UInt32).malloc(malloc_size, value)
clear_unused_bits if initial
end
def ==(other : BitArray)
return false if size != other.size
# NOTE: If BitArray implements resizing, there may be more than 1 binary
# representation and their hashes for equivalent BitArrays after a downsize as the
# discarded bits may not have been zeroed.
return LibC.memcmp(@bits, other.@bits, bytesize) == 0
end
def unsafe_fetch(index : Int) : Bool
bit_index, sub_index = index.divmod(32)
(@bits[bit_index] & (1 << sub_index)) > 0
end
def unsafe_put(index : Int, value : Bool)
bit_index, sub_index = index.divmod(32)
if value
@bits[bit_index] |= 1 << sub_index
else
@bits[bit_index] &= ~(1 << sub_index)
end
end
# :inherit:
def []=(index : Int, value : Bool) : Bool
bit_index, sub_index = bit_index_and_sub_index(index)
if value
@bits[bit_index] |= 1 << sub_index
else
@bits[bit_index] &= ~(1 << sub_index)
end
value
end
# Returns all elements that are within the given range.
#
# Negative indices count backward from the end of the array (-1 is the last
# element). Additionally, an empty array is returned when the starting index
# for an element range is at the end of the array.
#
# Raises `IndexError` if the starting index is out of range.
#
# ```
# require "bit_array"
#
# ba = BitArray.new(5)
# ba[0] = true; ba[2] = true; ba[4] = true
# ba # => BitArray[10101]
#
# ba[1..3] # => BitArray[010]
# ba[4..7] # => BitArray[1]
# ba[6..10] # raise IndexError
# ba[5..10] # => BitArray[]
# ba[-2...-1] # => BitArray[0]
# ```
def [](range : Range) : BitArray
self[*Indexable.range_to_index_and_count(range, size) || raise IndexError.new]
end
# Returns count or less (if there aren't enough) elements starting at the
# given start index.
#
# Negative indices count backward from the end of the array (-1 is the last
# element). Additionally, an empty array is returned when the starting index
# for an element range is at the end of the array.
#
# Raises `IndexError` if the starting index is out of range.
#
# ```
# require "bit_array"
#
# ba = BitArray.new(5)
# ba[0] = true; ba[2] = true; ba[4] = true
# ba # => BitArray[10101]
#
# ba[-3, 3] # => BitArray[101]
# ba[6, 1] # raise indexError
# ba[1, 2] # => BitArray[01]
# ba[5, 1] # => BitArray[]
# ```
def [](start : Int, count : Int) : BitArray
start, count = normalize_start_and_count(start, count)
if count == 0
return BitArray.new(0)
end
if size <= 32
# Result *and* original fit in a single int32, we can use only bitshifts
bits = @bits[0]
bits >>= start
bits &= ~(UInt32::MAX << count)
BitArray.new(count).tap { |ba| ba.@bits[0] = bits }
elsif size <= 64
# Original fits in int64, we can use bitshifts
bits = @bits.as(UInt64*)[0]
bits >>= start
bits &= ~(UInt64::MAX << count)
if count <= 32
BitArray.new(count).tap { |ba| ba.@bits[0] = bits.to_u32! }
else
BitArray.new(count).tap { |ba| ba.@bits.as(UInt64*)[0] = bits }
end
else
ba = BitArray.new(count)
start_bit_index, start_sub_index = start.divmod(32)
end_bit_index = (start + count) // 32
i = 0
bits = @bits[start_bit_index]
while start_bit_index + i <= end_bit_index
low_bits = bits
low_bits >>= start_sub_index
bits = @bits[start_bit_index + i + 1]
high_bits = bits
high_bits &= ~(UInt32::MAX << start_sub_index)
high_bits <<= 32 - start_sub_index
ba.@bits[i] = low_bits | high_bits
i += 1
end
# The last assignment to `bits` might refer to a `UInt32` in the middle of
# the buffer, so the last `UInt32` of `ba` might contain unused bits.
ba.clear_unused_bits
ba
end
end
# Toggles the bit at the given *index*. A `false` bit becomes a `true` bit,
# and vice versa.
#
# Negative indices count backward from the end of the array (-1 is the last
# element).
#
# Raises `IndexError` if *index* is out of range.
#
# ```
# require "bit_array"
#
# ba = BitArray.new(5)
# ba[3] # => false
# ba.toggle(3)
# ba[3] # => true
# ```
def toggle(index) : Nil
bit_index, sub_index = bit_index_and_sub_index(index)
@bits[bit_index] ^= 1 << sub_index
end
# Toggles all bits that are within the given *range*. A `false` bit becomes a
# `true` bit, and vice versa.
#
# Negative indices count backward from the end of the array (-1 is the last
# element).
#
# Raises `IndexError` if the starting index is out of range.
#
# ```
# require "bit_array"
#
# ba = BitArray.new(5)
# ba.to_s # => "BitArray[00000]"
# ba.toggle(1..-2)
# ba.to_s # => "BitArray[01110]"
# ```
def toggle(range : Range)
toggle(*Indexable.range_to_index_and_count(range, size) || raise IndexError.new)
end
# Toggles *count* or less (if there aren't enough) bits starting at the given
# *start* index. A `false` bit becomes a `true` bit, and vice versa.
#
# Negative indices count backward from the end of the array (-1 is the last
# element).
#
# Raises `IndexError` if *index* is out of range.
# Raises `ArgumentError` if *count* is a negative number.
#
# ```
# require "bit_array"
#
# ba = BitArray.new(5)
# ba.to_s # => "BitArray[00000]"
# ba.toggle(1, 3)
# ba.to_s # => "BitArray[01110]"
# ```
def toggle(start : Int, count : Int)
start, count = normalize_start_and_count(start, count)
return if count == 0
start_bit_index, start_sub_index = start.divmod(32)
end_bit_index, end_sub_index = (start + count - 1).divmod(32)
if start_bit_index == end_bit_index
# same UInt32, don't perform the loop at all
@bits[start_bit_index] ^= uint32_mask(start_sub_index, end_sub_index)
else
@bits[start_bit_index] ^= uint32_mask(start_sub_index, 31)
(start_bit_index + 1..end_bit_index - 1).each do |i|
@bits[i] = ~@bits[i]
end
@bits[end_bit_index] ^= uint32_mask(0, end_sub_index)
end
end
# returns (1 << from) | (1 << (from + 1)) | ... | (1 << to)
@[AlwaysInline]
private def uint32_mask(from, to)
(Int32::MIN >> (to - from)).to_u32! >> (31 - to)
end
# Inverts all bits in the array. Falses become `true` and vice versa.
#
# ```
# require "bit_array"
#
# ba = BitArray.new(5)
# ba[2] = true; ba[3] = true
# ba # => BitArray[00110]
# ba.invert
# ba # => BitArray[11001]
# ```
def invert : Nil
malloc_size.times do |i|
@bits[i] = ~@bits[i]
end
clear_unused_bits
end
# :inherit:
def reverse! : self
return self if size <= 1
if size <= 32
@bits.value = Intrinsics.bitreverse32(@bits.value) >> (32 - size)
elsif size <= 64
more_bits = @bits.as(UInt64*)
more_bits.value = Intrinsics.bitreverse64(more_bits.value) >> (64 - size)
else
# 3 or more groups of bits
offset = (-size) % 32
if offset != 0
# left-shifting, followed by bit-reversing in each group
# simplified bit pattern example using a group size of 8: (offset = 3)
#
# hgfedcba ponmlkji 000utsrq
# hgfedcba ponmlkji utsrqpon
# hgfedcba ponmlkji nopqrstu
# hgfedcba mlkjihgf nopqrstu
# hgfedcba fghijklm nopqrstu
(malloc_size - 1).downto(1) do |i|
@bits[i] = Intrinsics.bitreverse32((@bits[i] << offset) | (@bits[i - 1] >> (32 - offset)))
end
# last group:
#
# edcba000 fghijklm nopqrstu
# 000abcde fghijklm nopqrstu
@bits[0] = Intrinsics.bitreverse32(@bits[0] << offset)
else
# no padding; do only the bit reverses
Slice.new(@bits, malloc_size).map! { |x| Intrinsics.bitreverse32(x) }
end
# reversing all groups themselves:
#
# nopqrstu fghijklm 000abcde
Slice.new(@bits, malloc_size).reverse!
end
self
end
# :inherit:
def rotate!(n : Int = 1) : self
return self if size <= 1
n %= size
return self if n == 0
if size % 8 == 0 && n % 8 == 0
to_slice.rotate!(n // 8)
elsif size <= 32
@bits[0] = (@bits[0] >> n) | (@bits[0] << (size - n))
clear_unused_bits
elsif n <= 32
temp = @bits[0]
malloc_size = self.malloc_size
(malloc_size - 1).times do |i|
@bits[i] = (@bits[i] >> n) | (@bits[i + 1] << (32 - n))
end
end_sub_index = (size - 1) % 32 + 1
if n <= end_sub_index
# n = 3: (bit patterns here are little-endian)
#
# ........ ........ ........ .....CBA -> ........ ........ ........ ........
# ........ ........ ........ ........ -> cba..... ........ ........ ........
# 00000000 00000000 00000000 000edcba -> 00000000 00000000 00000000 000CBAed
@bits[malloc_size - 1] = (@bits[malloc_size - 1] >> n) | (temp << (end_sub_index - n))
else
# n = 7:
#
# ........ ........ ........ .GFEDCBA -> ........ ........ ........ ........
# ........ ........ ........ ........ -> BAedcba. ........ ........ ........
# 00000000 00000000 00000000 000edcba -> 00000000 00000000 00000000 000GFEDC
@bits[malloc_size - 2] |= temp << (32 + end_sub_index - n)
@bits[malloc_size - 1] = temp << (end_sub_index - n)
end
clear_unused_bits
elsif n >= size - 32
n = size - n
malloc_size = self.malloc_size
end_sub_index = (size - 1) % 32 + 1
if n <= end_sub_index
# n = 3:
#
# ........ ........ ........ ........ -> ........ ........ ........ .....CBA
# 00000000 00000000 00000000 000CBA.. -> 00000000 00000000 00000000 000.....
temp = @bits[malloc_size - 1] >> (end_sub_index - n)
else
# n = 7:
#
# BA...... ........ ........ ........ -> ........ ........ ........ .GFEDCBA
# 00000000 00000000 00000000 000GFEDC -> 00000000 00000000 00000000 000.....
temp = (@bits[malloc_size - 1] << (n - end_sub_index)) | (@bits[malloc_size - 2] >> (32 + end_sub_index - n))
end
(malloc_size - 1).downto(1) do |i|
@bits[i] = (@bits[i] << n) | (@bits[i - 1] >> (32 - n))
end
@bits[0] = (@bits[0] << n) | temp
clear_unused_bits
else
super
end
self
end
# Creates a string representation of self.
#
# ```
# require "bit_array"
#
# ba = BitArray.new(5)
# ba.to_s # => "BitArray[00000]"
# ```
def to_s(io : IO) : Nil
io << "BitArray["
each do |value|
io << (value ? '1' : '0')
end
io << ']'
end
# :ditto:
def inspect(io : IO) : Nil
to_s(io)
end
# Returns a `Bytes` able to read and write bytes from a buffer.
# The slice will be long enough to hold all the bits groups in bytes despite the `UInt32` internal representation.
# It's useful for reading and writing a bit array from a byte buffer directly.
#
# WARNING: It is undefined behaviour to set any of the unused bits of a bit array to
# `true` via a slice.
def to_slice : Bytes
Slice.new(@bits.as(Pointer(UInt8)), bytesize)
end
# See `Object#hash(hasher)`
def hash(hasher)
hasher = size.hash(hasher)
hasher = to_slice.hash(hasher)
hasher
end
# Returns a new `BitArray` with all of the same elements.
def dup
bit_array = BitArray.new(@size)
@bits.copy_to(bit_array.@bits, malloc_size)
bit_array
end
private def bit_index_and_sub_index(index)
bit_index_and_sub_index(index) { raise IndexError.new }
end
private def bit_index_and_sub_index(index)
index = check_index_out_of_bounds(index) do
return yield
end
index.divmod(32)
end
protected def clear_unused_bits
# There are no unused bits if `size` is a multiple of 32.
bit_index, sub_index = @size.divmod(32)
@bits[bit_index] &= ~(UInt32::MAX << sub_index) unless sub_index == 0
end
private def bytesize
(@size - 1) // 8 + 1
end
private def malloc_size
(@size - 1) // 32 + 1
end
end