[TriEmbed] arrays of function addresses Re: optimized switch statements Re: Hacking a fake vintage radio (with Arduino + Pi 0)
pete at soper.us
Wed Jul 1 18:50:10 CDT 2020
Would this constitute "threaded execution"? I recall being told how
Forth dispatches in a clever way at the end of each operation and the
use of "NEXT" seems similar (to my vague memory of the description).
One other trick users of C and C++ should consider is function
references in variables and parameters. Some time back I made a "simple
pin change" library to give folks three more interrupts with the
Atmega328, the one used with the Arduino Uno and Nano and others
(warning: only tested with that chip). It uses an array of functions
that resolve to either a dummy internal function or the user's desired
interrupt handler. If anybody is interested the code is here:
The C syntax for pointers to functions gets my vote for hardest to remember.
On 7/1/20 7:18 PM, Jon Wolfe via TriEmbed wrote:
> In an interesting coincidence, the place where I recall seeing the use
> of goto I described was also in a bytecode interpreter, for the “Pawn
> Scripting language” (which is really cool by the way, I’ve got it to
> emscripten, and run inside a browser. It is extremely fast for a
> bytecode interpreter)
> Check out line 208:
> That ‘NEXT’ macro is using a goto behind the scenes. Each block of
> code in between that labels (ie the semantic ‘case statement’
> equivalents) ends with a NEXT macro, so it may actually be faster than
> even a compiler optimized switch-case because there is no ‘loop’ logic
> needed, to cycle back around to the ‘switch’. Its really just a
> devilish jumping around inside that function.
> One could argue that ‘break’ and ‘continue’ statements used inside
> loops are really just dressed up ‘gotos’ with specific jump
> destinations. I’ve been writing code almost daily for close to 30
> years, and much of that time doing C or C++, and I’d estimate the time
> in between occasions where I used the goto keyword to be 2-5 years, so
> in other words, pretty rare. One of those uses can be for “breaking’
> out of a nested loop. Java has a “break <label>” statement that you
> can use to break out of an outer loop from within an inner loop.
> Standard C/C++ doesn’t have anything like that so you have to either
> use a flag, restructure your loops, or use a goto statement. I think
> it’s a matter of option, on a case by case basis which technique will
> lead to cleaner, easier to follow code in any particular situation.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the TriEmbed