97 lines
2.7 KiB
Ruby
97 lines
2.7 KiB
Ruby
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class Parslet::Source
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# A cache for line start positions.
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#
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class LineCache
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def initialize
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# Stores line endings as a simple position number. The first line always
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# starts at 0; numbers beyond the biggest entry are on any line > size,
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# but probably make a scan to that position neccessary.
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@line_ends = []
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@line_ends.extend RangeSearch
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end
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# Returns a <line, column> tuple for the given input position.
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#
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def line_and_column(pos)
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eol_idx = @line_ends.lbound(pos)
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if eol_idx
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# eol_idx points to the offset that ends the current line.
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# Let's try to find the offset that starts it:
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offset = eol_idx>0 && @line_ends[eol_idx-1] || 0
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return [eol_idx+1, pos-offset+1]
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else
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# eol_idx is nil, that means that we're beyond the last line end that
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# we know about. Pretend for now that we're just on the last line.
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offset = @line_ends.last || 0
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return [@line_ends.size+1, pos-offset+1]
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end
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end
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def scan_for_line_endings(start_pos, buf)
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return unless buf
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buf = StringScanner.new(buf)
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return unless buf.exist?(/\n/)
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## If we have already read part or all of buf, we already know about
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## line ends in that portion. remove it and correct cur (search index)
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if @last_line_end && start_pos < @last_line_end
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# Let's not search the range from start_pos to last_line_end again.
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buf.pos = @last_line_end - start_pos
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end
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## Scan the string for line endings; store the positions of all endings
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## in @line_ends.
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while buf.skip_until(/\n/)
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@last_line_end = start_pos + buf.pos
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@line_ends << @last_line_end
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end
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end
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end
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# Mixin for arrays that implicitly give a number of ranges, where one range
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# begins where the other one ends.
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#
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# Example:
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#
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# [10, 20, 30]
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# # would describe [0, 10], (10, 20], (20, 30]
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#
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module RangeSearch
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def find_mid(left, right)
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# NOTE: Jonathan Hinkle reported that when mathn is required, just
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# dividing and relying on the integer truncation is not enough.
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left + ((right - left) / 2).floor
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end
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# Scans the array for the first number that is > than bound. Returns the
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# index of that number.
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#
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def lbound(bound)
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return nil if empty?
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return nil unless last > bound
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left = 0
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right = size - 1
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loop do
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mid = find_mid(left, right)
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if self[mid] > bound
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right = mid
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else
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# assert: self[mid] <= bound
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left = mid+1
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end
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if right <= left
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return right
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end
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end
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end
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end
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end
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