class Epithet::Block58

# File lib/epithet.rb, line 225
def initialize(block_size, alphabet: Alphabet)
  @alphabet = alphabet.b.freeze
  raise ArgumentError, "invalid alphabet length" unless @alphabet.bytesize == 58
  @size = ((block_size * 8) / Math.log2(58)).ceil(0)
  @charsel = @alphabet.gsub(/[\^\-\\]/, '\\\\\&').freeze
  @blank = @alphabet[0] * @size
  @lut = @alphabet.each_byte.with_index.with_object("\0" * 256) { |(val, idx), lut| lut.setbyte(val, idx) }.freeze
end

# File lib/epithet.rb, line 244
def i2s(int)
  # Using divmod+setbyte is faster than Integer#digits under YJIT,
  # and about equal in plain MRI.
  alphabet = @alphabet
  out = @blank.dup
  idx = @size - 1
  n = int
  while idx >= 0 && n > 0
    n, rem = n.divmod(58)
    out.setbyte(idx, alphabet.getbyte(rem))
    idx -= 1
  end
  out
end

# File lib/epithet.rb, line 234
def inspect
  "#<#{self.class}:#{'%#016x' % (object_id << 1)} size=#{@size} alphabet=#{@alphabet}>"
end

# File lib/epithet.rb, line 261
def s2i(str)
  # By unrolling coefficients, this is ~8x faster than Horner's scheme
  #
  #   str.each_byte.inject(0) { _1 * 58 + @lut[_2] }
  #
  # at computing the inner product when using YJIT, by chunking
  # intermediate results into 64-bit integers.
  lut = @lut

  acc0 = lut.getbyte(str.getbyte(0)) * 7427658739644928 +
         lut.getbyte(str.getbyte(1)) * 128063081718016 +
         lut.getbyte(str.getbyte(2)) * 2207984167552 +
         lut.getbyte(str.getbyte(3)) * 38068692544 +
         lut.getbyte(str.getbyte(4)) * 656356768 +
         lut.getbyte(str.getbyte(5)) * 11316496 +
         lut.getbyte(str.getbyte(6)) * 195112 +
         lut.getbyte(str.getbyte(7)) * 3364 +
         lut.getbyte(str.getbyte(8)) * 58 +
         lut.getbyte(str.getbyte(9))

  acc1 = lut.getbyte(str.getbyte(10)) * 7427658739644928 +
         lut.getbyte(str.getbyte(11)) * 128063081718016 +
         lut.getbyte(str.getbyte(12)) * 2207984167552 +
         lut.getbyte(str.getbyte(13)) * 38068692544 +
         lut.getbyte(str.getbyte(14)) * 656356768 +
         lut.getbyte(str.getbyte(15)) * 11316496 +
         lut.getbyte(str.getbyte(16)) * 195112 +
         lut.getbyte(str.getbyte(17)) * 3364 +
         lut.getbyte(str.getbyte(18)) * 58 +
         lut.getbyte(str.getbyte(19))

                           lut.getbyte(str.getbyte(21)) +
                      58 * lut.getbyte(str.getbyte(20)) +
                    3364 * acc1 +
  1449225352009601191936 * acc0
end

# File lib/epithet.rb, line 239
def valid?(s)
  String === s && s.bytesize == @size && s.count(@charsel) == @size
end