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def Functions::substring( string, start, length=nil ) ruby_string = string(string) ruby_length = if length.nil? ruby_string.length.to_f else number(length) end ruby_start = number(start) # Handle the special cases return '' if ( ruby_length.nan? or ruby_start.nan? or ruby_start.infinite? ) infinite_length = ruby_length.infinite? == 1 ruby_length = ruby_string.length if infinite_length # Now, get the bounds. The XPath bounds are 1..length; the ruby bounds # are 0..length. Therefore, we have to offset the bounds by one. ruby_start = ruby_start.round - 1 ruby_length = ruby_length.round if ruby_start < 0 ruby_length += ruby_start unless infinite_length ruby_start = 0 end return '' if ruby_length <= 0 ruby_string[ruby_start,ruby_length] end