c-literal-limits-fast is an alias for `c-literal-limits' in `cc-engine.el'.

(c-literal-limits-fast &optional LIM NEAR NOT-IN-DELIMITER)

Return a cons of the beginning and end positions of the comment or
string surrounding point (including both delimiters), or nil if point
isn't in one. If LIM is non-nil, it's used as the "safe" position
to start parsing from. If NEAR is non-nil, then the limits of any
literal next to point is returned. "Next to" means there's only
spaces and tabs between point and the literal. The search for such a
literal is done first in forward direction. If NOT-IN-DELIMITER is
non-nil, the case when point is inside a starting delimiter won't be
recognized. This only has effect for comments which have starting
delimiters with more than one character.

Note that this function might do hidden buffer changes. See the
comment at the start of cc-engine.el for more info.