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dct_spec.rb
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dct_spec.rb
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# frozen_string_literal: true
RSpec.describe Dct do
it 'has a version number' do
expect(Dct::VERSION).not_to be nil
end
reference_dct_type2 = lambda do |vec|
(0..vec.length - 1).map do |k|
sum = 0
(0..vec.length - 1).each do |n|
idx = (2 * n + 1) * k
cos = Math.cos(Math::PI / (2 * vec.length) * idx)
sum += vec[n] * cos
end
sum
end
end
reference_dct_type3 = lambda do |vec|
(0..vec.length - 1).map do |k|
sum = 0.5 * vec[0]
(1..vec.length - 1).each do |n|
idx = n * (2 * k + 1)
cos = Math.cos(Math::PI / (2 * vec.length) * idx)
sum += vec[n] * cos
end
sum
end
end
describe 'dct_type2' do
describe 'size 3' do
it 'match result of reference implementation' do
vec = (1..3).map { |i| i}
expect(Dct.dct_type2(vec)).to eq(reference_dct_type2.call(vec))
end
end
describe 'size 128' do
it 'match result of reference implementation' do
vec = (1..128).map { |i| i}
expect(Dct.dct_type2(vec)).to eq(reference_dct_type2.call(vec))
end
end
end
describe 'dct_type3' do
describe 'size 3' do
it 'match result of reference implementation' do
vec = (1..3).map { |i| i}
expect(Dct.dct_type3(vec)).to eq(reference_dct_type3.call(vec))
end
end
describe 'size 128' do
it 'match result of reference implementation' do
vec = (1..128).map { |i| i}
expect(Dct.dct_type3(vec)).to eq(reference_dct_type3.call(vec))
end
it 'can invert DCTII with scaling' do
vec = (1..128).map { |i| i}
dct_type2 = Dct.dct_type2(vec)
inverted = Dct.dct_type3(dct_type2).map {|x| x * (2.0 / vec.length) }
vec.each.with_index { |x, i|
expect(x).to be_within(1e-7).of(vec[i])
}
end
end
end
end