I'm feeling "diverse" today
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It is an interesting approach and, as always, I will be very keen to see how it compares when it's finished.
I ditched it altogether! I found out the Arduino Stream class has a find() method which will allow you to find a string within a stream (without having to load it into a string first and use strstr()) So much for all this effort, although I will need to use something like the DFA machine to grab JSON from a weather service. The issue with that is fields can be in any order so I either load the fields into memory, or i use a DFA lexer. I'd rather use the lexer.
To err is human. Fortune favors the monsters.
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I ditched it altogether! I found out the Arduino Stream class has a find() method which will allow you to find a string within a stream (without having to load it into a string first and use strstr()) So much for all this effort, although I will need to use something like the DFA machine to grab JSON from a weather service. The issue with that is fields can be in any order so I either load the fields into memory, or i use a DFA lexer. I'd rather use the lexer.
To err is human. Fortune favors the monsters.
I find that coding effort is very rarely, if ever wasted, it goes into a black hole and comes out as ultra-energetic gamma radiation at a some later date. 15 years ago, I wrote a (micro) JS server to run applications via browser on any platform with plug-ins to pull data from misc devices/websites. I got side tracked and just had cause to go back to it. I wrote that in C and it will be much simpler in c# now (and much more x-platform), but it is still a good architectural reference point. Never wasted, the neurons are just better configured for next time...
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I wanted to load some JSON from a couple of web based APIs to get the local time and weather. The trouble is I didn't actually want to use JSON, because that's a nasty dependency. What about regex? There's no regex engine readily available to my IoT widget. Well, traversing a DFA state table that represents a regular expression in C++ is almost trivial. Generating that table is not. But I have a regex engine in C#, and it's capable of generating that table. So I whip up a little C# program to generate a C++ array representing the "DFA table" for a regular expression - basically the opcodes it needs to match the expression. And then some C++ code to traverse it. 3 languages Regex C++ C# To "parse" a fourth, a JSON subset In a really compact way. And I'm not even doing front-end web development - just a REST/JSON client.
To err is human. Fortune favors the monsters.
Why not parsing JSON in C# directly? That's a dependency on .NET's standard runtime library which ain't too bad.
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Why not parsing JSON in C# directly? That's a dependency on .NET's standard runtime library which ain't too bad.
Because first it would mean upgrading the SRAM on my device to something more than 512kB Then it would involve upgrading the processor to something in the GHz range And heck, it would involve adding a PC in there somewhere to actually run .NET. This is not a .NET device[^]
To err is human. Fortune favors the monsters.
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Because first it would mean upgrading the SRAM on my device to something more than 512kB Then it would involve upgrading the processor to something in the GHz range And heck, it would involve adding a PC in there somewhere to actually run .NET. This is not a .NET device[^]
To err is human. Fortune favors the monsters.
Things are getting insteresting! What and how do you compile C# down to? Can I imagine what you're doing to be similar to what the Unity developers are doing (compiling C# to C++ which then gets compiled to native code)?
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Things are getting insteresting! What and how do you compile C# down to? Can I imagine what you're doing to be similar to what the Unity developers are doing (compiling C# to C++ which then gets compiled to native code)?
I'm just basically using C# to generate an array for my C++ code to traverse. The C# code is a console application. I feed it a regular expression on the command line and it produces a small amount of C++ code to declare an array as its output - for example:
int16_t dfa_table[] = {
-1, 1, 6, 1, 34, 34, -1, 1, 12, 1, 117, 117, -1, 1, 18,
1, 110, 110, -1, 1, 24, 1, 105, 105, -1, 1, 30, 1, 120, 120,
-1, 1, 36, 1, 116, 116, -1, 1, 42, 1, 105, 105, -1, 1, 48,
1, 109, 109, -1, 1, 54, 1, 101, 101, -1, 1, 60, 1, 34, 34,
-1, 1, 66, 1, 58, 58, 0, 0
};That's a DFA table. What it is is a state machine encoded into an array. I have C++ code that can walk it in order to run the regular expression. The walking code is easy and efficient. Generating the array is not easy. That C# console application uses a regular expression engine I wrote (in C#) in order to generate that C++ array. The code to run the regular expression is simple and is in C++:
bool match(const int16_t* dfa, int16_t(read_cb)(void*), void* cb_state = nullptr) {
int tlen;
int tto;
int prlen;
int pmin;
int pmax;
int i;
int j;
int ch;
int state = 0;
bool done;
bool found = false;
int acc = -1;
ch = read_cb(cb_state);
while (ch != -1) {
acc = -1;
done = false;
while (!done) {
start_dfa:
done = true;
acc = dfa[state++];
tlen = dfa[state++];
for (i = 0; i < tlen; ++i) {
tto = dfa[state++];
prlen = dfa[state++];
for (j = 0; j < prlen; ++j) {
pmin = dfa[state++];
pmax = dfa[state++];
if (ch < pmin) break;
if (ch <= pmax) {
found = true;
ch = read_cb(cb_state);
state = tto;
done = false;goto start\_dfa; } } } } if (acc != -1) { return found; } ch = read\_cb(cb\_state); state = 0; } return false;}
To err is human. Fortune favors the monsters.
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I'm just basically using C# to generate an array for my C++ code to traverse. The C# code is a console application. I feed it a regular expression on the command line and it produces a small amount of C++ code to declare an array as its output - for example:
int16_t dfa_table[] = {
-1, 1, 6, 1, 34, 34, -1, 1, 12, 1, 117, 117, -1, 1, 18,
1, 110, 110, -1, 1, 24, 1, 105, 105, -1, 1, 30, 1, 120, 120,
-1, 1, 36, 1, 116, 116, -1, 1, 42, 1, 105, 105, -1, 1, 48,
1, 109, 109, -1, 1, 54, 1, 101, 101, -1, 1, 60, 1, 34, 34,
-1, 1, 66, 1, 58, 58, 0, 0
};That's a DFA table. What it is is a state machine encoded into an array. I have C++ code that can walk it in order to run the regular expression. The walking code is easy and efficient. Generating the array is not easy. That C# console application uses a regular expression engine I wrote (in C#) in order to generate that C++ array. The code to run the regular expression is simple and is in C++:
bool match(const int16_t* dfa, int16_t(read_cb)(void*), void* cb_state = nullptr) {
int tlen;
int tto;
int prlen;
int pmin;
int pmax;
int i;
int j;
int ch;
int state = 0;
bool done;
bool found = false;
int acc = -1;
ch = read_cb(cb_state);
while (ch != -1) {
acc = -1;
done = false;
while (!done) {
start_dfa:
done = true;
acc = dfa[state++];
tlen = dfa[state++];
for (i = 0; i < tlen; ++i) {
tto = dfa[state++];
prlen = dfa[state++];
for (j = 0; j < prlen; ++j) {
pmin = dfa[state++];
pmax = dfa[state++];
if (ch < pmin) break;
if (ch <= pmax) {
found = true;
ch = read_cb(cb_state);
state = tto;
done = false;goto start\_dfa; } } } } if (acc != -1) { return found; } ch = read\_cb(cb\_state); state = 0; } return false;}
To err is human. Fortune favors the monsters.
Ah, I get it. Thank you for the thorough explanation :)
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Ah, I get it. Thank you for the thorough explanation :)
No problem. I don't target .NET these days, as I spend most of time with tiny little gadgets. To me .NET is a means to an end. If I can use it to offload some of the heavy lifting my code would otherwise have to do I'll do that, of course. Otherwise I haven't really used it recently. I do have a lot of code I've written in C#, and used to use it professionally - sometimes I still will every once in awhile, but it's not my bread and butter anymore. The regular expression thing is a great example of being able to use it to offload work though - where an actual regular expression engine on the device would take up precious RAM and flash space, I was able to "outsource it" to an external C# app I only need to run once.
To err is human. Fortune favors the monsters.
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No problem. I don't target .NET these days, as I spend most of time with tiny little gadgets. To me .NET is a means to an end. If I can use it to offload some of the heavy lifting my code would otherwise have to do I'll do that, of course. Otherwise I haven't really used it recently. I do have a lot of code I've written in C#, and used to use it professionally - sometimes I still will every once in awhile, but it's not my bread and butter anymore. The regular expression thing is a great example of being able to use it to offload work though - where an actual regular expression engine on the device would take up precious RAM and flash space, I was able to "outsource it" to an external C# app I only need to run once.
To err is human. Fortune favors the monsters.
I'd go as far as to claim for everything to be means to and end. Programming something embedded in C++, it still is means to an end :p
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I'd go as far as to claim for everything to be means to and end. Programming something embedded in C++, it still is means to an end :p
Ha! Okay that's fair. But in this case, I mean I'll use it to facilitate my IoT development, rather than use it to make applications that are meant to be used standalone or even libraries from C#.
To err is human. Fortune favors the monsters.
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I wanted to load some JSON from a couple of web based APIs to get the local time and weather. The trouble is I didn't actually want to use JSON, because that's a nasty dependency. What about regex? There's no regex engine readily available to my IoT widget. Well, traversing a DFA state table that represents a regular expression in C++ is almost trivial. Generating that table is not. But I have a regex engine in C#, and it's capable of generating that table. So I whip up a little C# program to generate a C++ array representing the "DFA table" for a regular expression - basically the opcodes it needs to match the expression. And then some C++ code to traverse it. 3 languages Regex C++ C# To "parse" a fourth, a JSON subset In a really compact way. And I'm not even doing front-end web development - just a REST/JSON client.
To err is human. Fortune favors the monsters.
sounds awesome. when reading the comments and when start talking about tens of kilobytes, :(( :sigh: I know way out of my depth. Trying to figure out library and runtime differences of Regex/JSON and not getting anywhre Ill just fallback to Regex being many times older and many works of optimising and minimising. JSON format been great for the balance of human readability and reduced redundancy of XML, but where computers matter, bits is all that they care about.
