module RDoc::Markdown::ByteRuntime

Byte-offset replacements for the position helpers of the kpeg-generated parser runtime.

The generated runtime addresses +@string+ by character index, which makes every position lookup scan the string from its beginning when the input contains non-ASCII characters, so parse time becomes quadratic in the input size. Generated rule bodies only save and restore pos without inspecting it, so replacing these helpers is enough to switch the whole parser to byte offsets.

get_byte (the grammar’s ‘.`) consumes one character and returns its codepoint, exactly like the character-index runtime, so positions always stay on character boundaries and the only observable difference is the position values themselves. The input must be validly encoded in an ASCII-compatible encoding.

The error-reporting helpers of the generated runtime (current_line, current_column, …) are left as-is and would misreport locations when given byte offsets. They are unreachable: markdown is deliberately designed to parse any input somehow rather than fail (the root rule ‘Doc = Block*` cannot fail), so a parse failure means a bug in the grammar itself, and nothing in RDoc invokes raise_error or show_error. Make these helpers byte-aware before using them for anything.

# File lib/rdoc/markdown/byte_runtime.rb, line 59
def get_byte
  byte = @string.getbyte(@pos)
  return nil unless byte

  if byte < 0x80
    @pos += 1
    byte
  else
    @scanner.pos = @pos
    # /./ interprets the character in the string's own encoding
    char = @scanner.scan(/./m)
    @pos = @scanner.pos
    char.ord
  end
end

# File lib/rdoc/markdown/byte_runtime.rb, line 75
def get_text(start)
  @string.byteslice(start, @pos - start)
end

# File lib/rdoc/markdown/byte_runtime.rb, line 51
def match_string(str)
  len = str.bytesize
  if @string.byteslice(@pos, len) == str
    @pos += len
    str
  end
end

# File lib/rdoc/markdown/byte_runtime.rb, line 43
def scan(reg)
  @scanner.pos = @pos
  if @scanner.skip(reg)
    @pos = @scanner.pos
    true
  end
end

# File lib/rdoc/markdown/byte_runtime.rb, line 35
def set_string(string, pos)
  @string = string
  @string_size = string ? string.bytesize : 0
  @pos = pos
  @position_line_offsets = nil
  @scanner = string ? StringScanner.new(string) : nil
end