how to get file postion

[Ye Wenbin]

Hi,
If I want to access part of a big file, so it is important to build
a index of the file. But if use insert-file-contents to read the
whole file, I don't know how to convert between point in the buffer
to the position in the file(for unix file, point-1 is ok, but not for
dos file). Although using insert-file-literally is a choice, I have to
handle "\r\n" and others labor things. So I wonder whether there is
a function to convert point to offset postion in the file.
Thank you!

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Best regards.
Ye Wenbin