c# - Performing bitwise left shifts on "signed" data in Java -- better to move to JNI? -

-

i've been asking questions on hex , bitwise manipulation (here , elsewhere) past week trying wrap head around representation in java. after googling , chagrin must ask 1 final time how perform logical arithmetic on bits ought unsigned, represented signed in java.

okay: porting c# program java. program deals bitmap manipulation, , such of data in app represented byte, unsigned 8-bit integer. there many suggestions instead use short data type in java in order "mimic" close possible unsigned 8-byte integer.

i don't believe that's possible me c# code performing various many shifting , and operations byte data. example, if data byte array, , block of code exists in c#:

int cmdtype = data[pos] >> 5; int len = (data[pos] & 0x1f) + 1;  if (cmdtype == 7) {     cmdtype = (data[pos] & 0x1c) >> 2;     len = ((data[pos] & 3) << 8) + data[pos + 1] + 1;     pos++; }

it's not simple matter of casting data short , being done work in java. far logic concerned requirement data stay in 8-bit unsigned significant; 16-bit unsigned screw math above up. right here? indeed, after having "fake casting" byte 0xff , char in java , not getting right results, afraid hit dead end.

now, in part of code, performing bitmap pixel manipulation. since it's long running process, decided make call native code through jni. realized in there use uint8_t data type , closest representation c# byte data type.

is solution make data-dependent functionality operate in jni? seems highly inefficient, both rewrote , perform. solution redo math in java logic remains same? seems right, has potential induce aneurysm, not mention faulty math.

i appreciate , suggestions.

just note: cannot cast directly short, because negative numbers logically extended.

that is, byte 1111 1101 (-5) when directly cast short result in 1111 1111 1111 1101 (-5), not 0000 0000 1111 1101 (253). must remove leading ones , operation when cast:

short shortvalue = ((short)(bytevalue)) & 0xff;

i know complex bit manipulation possible, because have done exact thing in handling legacy binary messaging protocol java swing application. highly recommend somehow abstracting away have deal once. whether means wrapping "bytes" in class store them shorts , handle conversion operations, or defining static utility conversion , bit operation in 1 pass, store bytes.


Comments

Post a Comment

Popular posts from this blog

android - Spacing between the stars of a rating bar? -

-
ho can set spacing beween stars? thats ratingbar: ratingbar = (ratingbar) inflater.inflate(r.layout.ratingbar, null); ratingbar.setlayoutparams(new layoutparams(layoutparams.wrap_content, layoutparams.wrap_content)); the layout: <?xml version="1.0" encoding="utf-8"?> <ratingbar xmlns:android="http://schemas.android.com/apk/res/android" style="@style/mystyle" android:layout_alignparentright="true" android:layout_height="19dp" android:layout_width="wrap_content" android:numstars="5"> </ratingbar> the style: <style name="mystyle" parent="@android:style/widget.ratingbar"> <item name="android:progressdrawable">@drawable/android_r2_ratingstar_yellow</item> <item name="android:indeterminatedrawable">@drawable/android_r2_ratingstar_grey</item> </style> thanks, cheers you have ...
Read more

html - Instapaper-like algorithm -

-
does of algorithm extracts contents webpage? instapaper ? there 2 steps instapaper does: find main content block on page (excluding headers, footers, menus etc) from content block extract , format text to find content block (typically html block element, div containing key page text content) instapaper uses algorithm 1 used readability . can @ source of readability.js see what's going on, @ core tries find area on page highest text/link ratio, although has other simple scoring metrics (e.g. off top of head, things ratio of text commas, para elements etc) go heuristics. once have identified root node element, relevant content, you'll need format it, if want can pull node element containing text out of source document , insert yours, in reality you'll want remove existing styles , apply own, standard , feel. if want output nice text-only can use jericho's renderer . update1 : should mention else instapaper - follow 'pagination' links (...
Read more

c# - How to execute a particular part of code asynchronously in a class -

-
i creating speech recognition engine that's going respond user commands.i have created button enable , disable speech recognition per user convenience.i have used dispose() of speech engine disable speech recoginition.here code private void button1_click(object sender, routedeventargs e) { engineon = !engineon; if (engineon) { speechengine = speech.createspeechengine(); //speech class creates , returns new speech engine. speechengine.audiolevelupdated += new eventhandler<audiolevelupdatedeventargs>(speechengine_audiolevelupdated); // use system's default microphone speechengine.setinputtodefaultaudiodevice(); speechengine.loadgrammar(new dictationgrammar()); // start listening speechengine.recognizeasync(recognizemode.multiple); } else { speechclass.myengine.dispose(); } } but disposal of speech obj...
Read more