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| JamesTait | Good morning all, happy Youth Day! :-D | 08:44 |
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| aquarius | o hai dobey :) | 14:25 |
| dobey | hey | 14:25 |
| aquarius | how's it going? | 14:26 |
| dobey | ok | 14:26 |
| dobey | you? | 14:26 |
| aquarius | actually, pretty well, modulo annoyance that porting C to JS is harder than I was hoping it would be :) | 14:26 |
| dobey | you're rewriting some C code in JS? | 14:27 |
| aquarius | ya. Echonest's song recogniser, echoprint, is open source, which is rather nice. But I don't want native code; I figured it'd be doable to port the recogniser to pure client-side JavaScript; then I could have something shazamish without compilation and cross-platform. | 14:28 |
| aquarius | (ignore, for the moment, how you get the song data *into* the browser; that's doable with the web audio API) | 14:28 |
| aquarius | I could use emscripten or something to compile the C to JS, but that seems massively overkill; it's just doing manipulation on arrays of numbers, so I thought I'd reimplement it in JS. | 14:29 |
| aquarius | (also, emscripten assumes you know a lot more about C than I do.) | 14:29 |
| dobey | is there a C lib too? i thought it was C++ | 14:29 |
| aquarius | C++, sorry | 14:30 |
| aquarius | the recogniser has three stages: whiten, subband analysis, and creating the fingerprint. The first two stages were fine -- the meat of the code is practically unchanged between C and JS (as I say, it's just doing operations on a big array of numbers, even if that big array in C++ is actually a block of memory) | 14:30 |
| aquarius | the third stage, fingerprinting... it's confusing me, 'cos the code does C-ish things like index into an array with a negative index...which is obviously fine in C, where it's all just pointers under the covers, but not at all fine in JS, where arrays are a real thing rather than just syntactic sugar for memory access. | 14:31 |
| aquarius | that means I have to understand what the code's doing, not just blindly port it...and that's hard. Or it's hard for me, anyway :) | 14:31 |
| dobey | uh, negative index in C is not fine | 14:33 |
| aquarius | dobey, I invite you to consider https://github.com/echonest/echoprint-codegen/blob/master/src/Fingerprint.cxx#L115 | 14:33 |
| dobey | aquarius: negative index in C results in undefined behavior | 14:34 |
| aquarius | j loops from 0 up to SUBBANDS. k loops from 0 up to nbn. Thus, pE[j-SUBBANDS*k] is pE[ (a number smaller than SUBBANDS) - SUBBANDS * (a positive number) ]. | 14:35 |
| dobey | a[-1] /may/ give you the last element of a[], but i don't think it is guaranteed to do so | 14:35 |
| aquarius | I can't see how that's anything other than negative? | 14:35 |
| dobey | right. i didn't say that the code wasn't doing that. i said it's undefined. i also don't know what SUBBANDS is. | 14:36 |
| aquarius | defined as 8 | 14:36 |
| aquarius | this sort of thing is why I'm finding this difficult :) | 14:36 |
| aquarius | originally I was pinging you about the whole call-this-library-from-ctypes-so-I-can-write-a-test-suite thing | 14:38 |
| dobey | right | 14:38 |
| aquarius | but in the end you convinced me that that was either hard or impossible, so I just dropped a load of print statements into the executable and ran the executable and piped the output to a text file, and then parsed the text file from js to write the test suite :) | 14:39 |
| dobey | http://stackoverflow.com/questions/4006736/c-negative-array-index | 14:40 |
| dobey | i don't think c++ defines arrays differently, but it might | 14:40 |
| aquarius | right. | 14:43 |
| dobey | so that code in echoprint is buggy | 14:43 |
| aquarius | I have tweeted at the echonest people to whine at them | 14:43 |
| aquarius | for extra hilarity, JS appears to be treating floating point stuff with different precision than C++ does, but I have decided to ignore that for now -- the numbers come up pretty close to being the same, and I'm secretly hoping that that means that the fingerprints will be the same | 14:44 |
| aquarius | if it doesn't mean that, then I get to cry and go back and fix that, but that sounds like major hassle :) | 14:44 |
| dobey | oh yeah, floating point. fun times that | 14:45 |
| dobey | you're probably going to be crying :) | 14:45 |
| aquarius | right :) | 14:48 |
| aquarius | but the fingerprint code is what's killing me right now. I was really hoping to not have to walk through it line-by-line by hand and understand it all :( | 14:49 |
| aquarius | all the variables being called stuff like Eb and pE is not helping, I have to say. | 14:49 |
| dobey | i don't see any other way. especially given their variable names | 14:49 |
| dobey | heh | 14:49 |
| * aquarius grins | 14:49 | |
| dobey | I presume Eb is some sort of class though | 14:49 |
| aquarius | tbh the goal was to have something shazamish on Ubuntu, but it's not clear to me whether the Touch browser will support modern stuff like the web audio API anyway; the Qt WebKit implementation is quite a way behind on this sort of thing | 14:50 |
| aquarius | meaning that this little project is very rapidly approaching the tipover point away from "that'd be a fun little hack" into "the hell with this hard work, I have paid things to do" :) | 14:51 |
| dobey | i suppose it wouldn't be terribly hard to write an echoprint app in C++ though | 14:51 |
| dobey | aside from the fact that code is apparently buggy | 14:52 |
| dobey | does echoprint-codegen have a testsuite itself that's easy to run from "make test" or something? | 14:53 |
| aquarius | hahahahahaha | 14:57 |
| dobey | was afraid of that | 14:57 |
| aquarius | aquarius@faith:~/Programs/Others/echoprint/echoprint-codegen/src$ grep test * | 14:57 |
| aquarius | AudioStreamInput.cxx: // Not an exhaustive list. ogg and rm could be added if tested. | 14:57 |
| aquarius | grep: echoprint-codegen-ios: Is a directory | 14:57 |
| aquarius | no. :-) | 14:57 |
| dobey | i got that much from the maniacal laughter | 14:58 |
| aquarius | it wouldn't be hard to write a C++ app -- just use the library | 14:59 |
| aquarius | but I'm not interested in C++ :-) | 14:59 |
| aquarius | someone else could do that, though | 15:00 |
| aquarius | elleomea wrote "eyrie" for the N9 a while back which does this, so that should be even easier to port. | 15:00 |
| dobey | a test suite would be nice though; then i could set up a daily build which runs the tests on arm, i386, and amd64 | 15:02 |
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