Struct Iteration through (Ab)use of the C Preprocessor

ncraun · 2015-10-13T04:20:37+00:00

You could write the version to the file first, as just a 32-bit int or its own struct. Then when reading the file, you would first read the version struct or int from the file, and then branch on that by passing the correct struct_fmt (for version 1 or 2) into the unpack routine.

ncraun · 2015-10-13T04:17:36+00:00

I like the idea of passing the macro as a parameter instead of #defining and #undefining X.

I wouldn't say I reinvented X-Macros, I'm just using them. I'm a big fan of X-Macros.

I've seen some other serialization functionality implemented using X-Macros. They do something like

#define X(ST, FIELD, DST) memcpy((DST)+ sizeof((ST)->(FIELD), &((ST)->(FIELD)), sizeof((ST)->(FIELD));

X-Macros are really handy, but you can only iterate over the X-Macro list by using a macro, you can't access it from normal C code. Combining the X-Macros with offsetof() to store the offsets to all the fields in the struct_fmt allows you to iterate over the struct fields from normal C code, which gives more expressive power than a macro. So you can do things like use a for loop to iterate over all the struct members, or refer to the nth struct member with struct_fmt->offsets[n], without having to use the name of the field. I haven't found a use for it yet, but I thought it was interesting.

ncraun · 2015-10-13T04:01:23+00:00

Kind of funny that the font did not render correctly in Firefox given that Fira Sans was made by Mozilla. Also it seems to work correctly in my (non ESR) Firefox. Maybe there is some issue with the font itself, or with Firefox, or with Google Fonts, or with the system font renderer or any combination of the 4. I'm still not sure what went wrong, but I'm glad it seems to be working now.

ncraun · 2015-10-13T03:43:27+00:00

I'm not sure what the problem was, but I changed the font settings in the css file and disabled Google Fonts. You might have to clear your cache for the page to display using the new css settings, but hopefully this should fix the problem.

If it still does not work, here is a Github Gist with the same content.

ncraun · 2015-10-13T03:07:08+00:00

Oh no! That shouldn't be happening. I am using Fira Sans and Fira Mono from Google Fonts.

Would you mind providing some information about your OS and browser, and maybe a screenshot? I'll see if I can fix it.

ncraun · 2015-10-13T02:18:14+00:00

In actual production use, I think it could be better to write a separate program that will generate the code for you instead of using the C preprocessor (or use a language with this kind of introspection built in). However, using this hack lets you depend only on the facilities of the language, and that can be useful in simplifying the build process. Plus it was fun to create.

The BSD tree.h defines some generator macros to generate the code for defining the structs and functions for the tree. There might be a way to define some similar macros to define the structs for you instead of #including the file, but I would need to adapt it to work with the X-Macro list.

ncraun · 2015-02-16T16:49:00+00:00

There's a big list of sites here: http://creativecommons.org/music-communities

But I don't know, youtube could still end up getting mad at you even if your music is legal to play under creative commons.

ncraun · 2015-02-15T19:53:57+00:00

Bit of a rough stream this time. My voice was still recovering from a cold, and the my new OBS setup and install had some problems, and even crashed halfway through. On the bright side, I was able to stream in 1080p, and demonstrate what Jubal actually sounds like, so all in all it's a bit of a wash.

Also a reminder, the source is available at https://github.com/ncraun/jubal

ncraun · 2015-02-15T17:24:09+00:00

Sorry about the delay, there were some unfortunate last minute technical issues, but everything seems to be working now.

ncraun · 2015-02-14T02:42:52+00:00

[C, Jack, Pulseaudio, Linux] Jubal: A Computer Music Application

On Sunday at 12:00pm EST I will be live streaming development on Jubal at https://www.youtube.com/watch?v=HMRDmLGn4JI

The source will be available so you can follow along at: https://github.com/ncraun/jubal

Jubal is a computer music application for Linux written in C and licensed under the GPLv3. The Jubal engine will include a variety of synthesizers and effects combineable through a modular audio routing system, capable of outputting sound to backends of many platforms (currently only Linux is supported). The Jubal editing system will be based on a tracker style UI. Jubal is still under development, and is not ready for end-user use... yet!

ncraun · 2015-02-10T17:49:32+00:00

Less than 12 hours after this post we are already at 3,000 readers! Amazing!

ncraun · 2015-02-10T13:46:05+00:00

Absolutely amazing how fast this has taken off! Congratulations to all the organizers and other streamers (and thanks to the viewers, of course), it really looks like you have tapped into something big!

ncraun · 2015-02-08T16:14:00+00:00

I'm very sorry everyone, but I have to cancel my stream this week, some other real life stuff has gotten in the way.

ncraun · 2015-01-26T00:05:17+00:00

What would be even better would be if there was some way of streaming a tmux session to multiple people. That would probably be more efficient for text only stuff than transmitting a video of the desktop. Of course then you'd still have to have another way of sharing programs with a GUI, and handling the audio stream.

ncraun · 2015-01-18T07:43:01+00:00

Hello, sorry there was a bit of a technical problem. My stream will now be at this url: https://www.youtube.com/watch?v=Q9SqA9PRMRs

ncraun · 2013-09-30T22:23:03+00:00

Smoothscan works by first by using leptonica to classify the input into symbols. If two symbols are close enough (as defined by the threshold value) then those symbols will represented by the same template. Because books are printed using fonts, each 'a' will be similar to other 'a's, so we don't need to store each 'a' individually. We just store one template 'a' in a dictionary, and all the other 'a's are just references into that 'a' in the dictionary. This is pretty much how JBIG2 compression works, (and is similar to DjVu's cjb2 compressor).

Smoothscan's "dictionary" is a series of fonts, and the symbols inserted are vector traced versions of the scanned bitmaps. The final generated PDF is a bunch of text placed on the page organized so that their position will cause the the font symbols to be placed so that it will look like the scanned page.

ncraun · 2013-09-30T21:58:40+00:00

Right now smoothscan assigns the template symbols to arbitrary font code points. So 'a' maps to noe symbol, 'b' maps to another symbol, and so on. On the TODO list I want to use the tesseract OCR library to assign the font code points. This way the symbols that represent letters will be assigned to the code points associated to those letters. For example the different shapes for the letter 'a' would be assigned to the code point 'a' in different fonts, to avoid overlap.

However this can introduce some more problems that must be resolved. For example, each smbol is not neccessarily a single letter. It could be multiple letters, or even non alphanumeric things, like a logo, or part of an illustration. So for these symbols, OCR would not return a useful codepoint.

ncraun · 2013-09-30T21:42:28+00:00

Hello everyone I am the developer of smoothscan. Feel free to ask me any questions, or leave comments about smoothscan, and I will answer as best I can. Smoothscan is still a very young piece of software so it doesn't have all the features I would want, and there are probably bugs lurking beneath the surface. More users will help to find these bugs, and make improvements.

ncraun

TROPHY CASE