I have several questions that are related to how programs link to one another.
Suppose I open a Java applet in Google Chrome. How does Google Chrome know where to find Java on my computer?
Suppose I include a standard library in a C program. How does the compiler know where to find that library?
Suppose I download one program that depends on another program. For example, BCFtools depends on the zlib library. How do I ensure that the first program can find and use the second program?
I have some familiarity with how the PATH variable is used in bash. However, I don't understand how some programs are able to "find" other programs that have been installed. Sorry if this is a rudimentary question but I failed to find anything on this online.
Related
So I recently wrote a chat bot which relies on lua and luasocket to respond to a twitch stream's chat. It's very basic and has various files it reads/writes to. It runs from the local computer. I finally got it working perfectly and now I'm interested in potentially distributing it to streamers who would get the most practical usage out of it.
But I can't just give them the files and lua script; they wouldn't be able to run it. They would need an interpreter and they would need to set up luasocket. With very little experience this is a very daunting task. Even I struggled to properly get luasocket working to make this bot.
So my question: Is there a way to package the lua interpreter and luasocket library such that I can give my bot to other people in an easy to use and practical manner? Preferably a .exe file, but really anything that doesn't require them to go out and set up the entire language and script dependencies on their own.
I'm working with ESP8266 and I don't want to use Lua for the whole project, I just want to run a few snippets of Lua code, received from wifi/sd card. I'd need to start a Lua environment and run the scripts, which would then eventually call some native functions for low level tasks. In other words, I just want to use Lua as simple scripting language (as it's intended to be) to implement some dynamic behavior. Is it possible? Is there any build of lualib for arduino?
Thanks in advance!
You can simply embed Lua in a extlibs/ folder for example and link to it when compiling your program.
There is existing Lua binaries but building it yourself is easy and better (as it's multiplatform).
OK, I know both answers told me I can just embed the code into my project, however, I found out I need to make some small changes. I made an example working project available here and the following list of changes had to be made:
The flags LUA_32BITS and LUA_USE_LONGJMP (C exception handling) were enabled
The following libraries were excluded: io, os, package, coroutine
The following functions were removed from C API: luaL_fileresult, luaL_execresult, luaL_loadfile, luaL_loadfilex, luaL_dofile, luaB_loadfile, luaB_dofile
Lua output messages are redirected to the Serial interface, check tinylua.h, tinylua.cpp and lauxlib.h to change this behavior
Hope this helps!
The ESP8266 has up to 4MB of program storage. Theoretically you can get up to 16MB as the datasheet specifies.
As I remember, compiling an amalgamated version of Lua (all sources in one file), occupies less than 100kb.
So, you can compile the Lua library and use it as needed on esp8266, even using Arduino IDE.
But you will get NAKED Lua if you do so... No nifty libraries to control Wifi, serial, SD, ports... You would have to provide that in C, or use NodeMCU code as you need.
You can try LuaJIT and access C code directly from Lua, cutting out the need for writing libraries. I have no idea of how you would compile it to Esp8266, or if anyone have tried this before, but you can do it "for science" and tell us how it turned out.
Sometimes in s/w companies, customers provide data in multiple formats. There are linkable and executable data that are said to be "Rehosted" and compiled object files that are said to be "Retargeted". I am trying to understand what rehosting and retargeting mean in this area. Is it similar to the Bootstrap theory in computer science? I have the understanding of the following process (if not incorrect):
PROBLEM:
I need to write a compiler for a new language called "MyLang" to run on PowerPC
Solution:
1. I need to write a compiler for a language "MyLang-Mini"; a subset of "MyLang" to run on PowerPC.
2. I need to write a compiler for "MyLang" using "MyLang-Mini" to run on PowerPC.
3. I run the compiler obtained from no. 1 through the compiler obtained from no. 2 to
obtain the compiler for MyLang to run on PowerPC.
IN BESPOKE "T" DIAGRAM (...ISH):
MyLang PowerPC MyLang PowerPC
MyLangMini MyLangMini PowerPC PowerPC(instr.)
PowerPC(instr.)
What I am getting confused about is rehosting and retargeting. How are they coonected to this concept? What am I rehosting and retargeting if I have some binary data such as .exe or .obj? I would appreciate some detailed explanation if possible please!
I know that this will embark onto "CROSS-COMPILERS", but would prefer expert opinions to be sure.
Thanks in advance.
I now know that in s/w engineering:
REHOSTING - If you have a third-party application linkable/executable that requires usage on your host machine, you do rehosting. The target in this case are most often the same (OS platform, processor, etc.). In worst case, there is a virtualisation required. The rehosted application will run as if it was one of the application running in the host machine
RETARGETTING - If you have a third-party source code, you might need to recompile that to match with your target environment. It may also be that you have third-party .o or .obj compiled models and you want to link them with your source code (retargeted) in order to host it on a host machine. Just like REHOSTED application, it will be as if the application was installed on the host machine.
It will be good to know how this is similar to the compiler rehosting and retargeting. Sorry, I am a newbee is this area and will appreciate even a slap on the wrist.
I am a newbie to industry and as a part of my internship I have been assigned the above project.I have no experience in how to go about porting a particular application to a different OS.
So far,i have tried to understand the basic structure of a component(thats what an application is called IOS-XR) but as far as I can understand,porting wireshark will also require porting the libpcap lib to XR.
Can someone please shed some light as to how should i go about approaching it?
I know nothing about QNX;
However, I will note that Wireshark has a lot of dependencies on various libraries:
Some examples;
libgLib
libgtk
libffi-5
libfontconfig-1
libfreetype-6
libintl-8
libjasper-1
libjpeg-8
liblzma-5
libpixman-1-0
libpng15-15
libtiff-5
libxml2-2
...
Are these libraries available on QNX ?
With respect to libpcap:
libpcap is needed for capturing files. If not available, it certainly would need to be ported. I could imagine that this might be a large effort given that presumably the code is presumably quite dependent upon the exact OS capabilities to get access to the network level data.
For information about developing Wireshark (on Windows and *nix) see the
Wireshark Developer's Guide.
I want to open libraries, because currently I want to see the algorithms used for drawing, modify them and implement them in my program. For example: I have tried to create an algorithm on my own for lines. But I failed. And even if I had succeeded, I fear that it might not give the same result as the algorithm in the libraries. And I don't want this to happen. That's why I want to copy the algorithms used for the methods in libraries. And I really hope that this will help me create the application I'm currently working on and with other applications in the future.
I tried to open the libraries with a code editor. But I had troubles finding the libraries- I don't really know where are they placed nor in what files are their codes stored.
How to open a Java library? Or is there a place in the Internet where the code is uploaded?
It sounds like what you want is to get inside the standard Java libraries (so you can see the code for methods like Graphics.drawLine()).
You can download the source files from the same place you got the JDK, if you are on Windows or Linux. For the Mac, see this question. You can even set up Eclipse so that you can debug into that source as if it were your own code.
However, you will probably not find line-drawing code in Java in these libraries - the Graphics implementation will almost certainly use native methods, and may just call existing methods in the OS.
If you are specifically looking for line drawing algorithms, another option would be to look at the Wikipedia page for the Bresenham (aliased) or Wu (antialiased) algorithm.
Edit:
The part of a Graphics2D call that actually puts pixels on the screen is probably inside a system call and therefore the source would not be available.
A java vector graphics library like Batik might have source for some of these algorithms, but probably relies on the Graphics2D calls for most of them. So, you might look for a comprehensive vector graphics library written in a language other than Java, where those graphics calls do not already exist by default.
Alternately, checking the table of contents for a computer graphics book might point you at a variety of algorithms that you could look up on Wikipedia.
For any given library:
Make sure to obey all licenses when using another's code
If you are referring to the Java SDK source code, you can find it here: http://grepcode.com/
If the project is open source, you can usually just get the source from the project website. No problem, though make sure to obey their license.
If the project is NOT open source, well, then you're in a pickle licensing wise, so I do NOT endorse this, however, you would need to use a Java Decompiler such as JD-Gui
As far as what drawing algorithms to use, there are so many different ones (obviously, people have been trying to draw quickly for many many years), your best bet is to figure out exactly what you need to do and then search for that specific need separately. There isn't really a good repository of ALL of them, except maybe wikipedia.
If you are using the libraries they are on your classpath. Check out how to figure out your classpath in whichever IDE you are using and you can find the JARs you depend on. If they are packaged with sources all you need to do it unjar them and look at the sources.
If you don't have access to the sources you can get the code using a Java Decompiler.
If you are trying to look at a standard Java library, see the other answers about getting the source to the JDK.
If you are interested in an open source library (such as something maintained by the Apache project), look on the site of the project for a 'source jar' which you can open with a standard zip utility.
If the library you want is not open source or you cannot find the source for it, you can try to decompile it. If you are using Eclipse, try this decompiler.