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# frozen_string_literal: true
module TTFunk # rubocop: disable Style/Documentation # false positive
# Bit crunching utility methods.
module BinUtils
# Turn a bunch of small integers into one big integer. Assumes big-endian.
#
# @param arr [Array<Integer>]
# @param bit_width [Integer] bit width of the elements
# @return [Integer]
def stitch_int(arr, bit_width:)
value = 0
arr.each_with_index do |element, index|
value |= element << (bit_width * index)
end
value
end
# Slice a big integer into a bunch of small integers. Assumes big-endian.
#
# @param value [Integer]
# @param bit_width [Integer] bit width of the elements
# @param slice_count [Integer] number of elements to slice into. This is
# needed for cases where top bits are zero.
# @return [Array<Integer>]
def slice_int(value, bit_width:, slice_count:)
mask = (2**bit_width) - 1
Array.new(slice_count) do |i|
(value >> (bit_width * i)) & mask
end
end
# Two's compliment to an integer.
#
# @param num [Integer]
# @param bit_width [Integer] number width
# @return [Integer]
def twos_comp_to_int(num, bit_width:)
if num >> (bit_width - 1) == 1
# we want all ones
mask = (2**bit_width) - 1
# find 2's complement, i.e. flip bits (xor with mask) and add 1
-((num ^ mask) + 1)
else
num
end
end
# Turns a (sorted) sequence of values into a series of two-element arrays
# where the first element is the start and the second is the length.
#
# @param values [Array<Integer>]
# @return [Array<Array(Integer, Integer)>]
def rangify(values)
values
.slice_when { |a, b| b - a > 1 }
.map { |span| [span.first, span.length - 1] }
end
end
BinUtils.extend(BinUtils)
end
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