[help-3dldf] Re: all intersections between two paths

[Hans Hagen]

Laurence Finston wrote:

> I don't think there's anything _wrong_ with it.  As I understand it,
> where tail recursion is possible, there is indeed no problem.
> Roughly speaking, and again as I understand it,
> in C and C++, the price of a function call
> is a stack frame, whereas the price of a loop is a handful of machine
> instructions.

most cpu's are optimized for that kind of stack handling, as are compilers,

> The price of an additional, recursive call to a function is another stack
> frame, whereas the price of an additional iteration is testing a
> conditional and a jump, i.e., negligible.

in this case, a few hundred stack frames are neglectable to what other threads 
in your OS may be doing; there are also languages that are build around 
recursion (functional languages and such)

> I don't know whether optimizing compilers (or perhaps the run-time system?)
> can recognize where tail recursion is possible and eliminate
> stack frame nesting;  nor do I know how a programmer could tell the
> compiler to do this, where possible, nor whether it would be wise for a
> programmer to depend on this behavior.  If you or anyone else knows
> about this subject, I'd be very interested in learning more.

in general, in languages like tex/mp, copying data structures take the most 
time, so don't worry about speed-up here; (in tex for instance, fully 
expandable, recursive macros are way faster than loops with counters)

Hans

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