Gwynne's Blog

The post title does not decieve; the ship’s warp drive now works.

That was an adventure in arctangents, power-of-two exponents, multiply-add operations, rounding errors… I have to say, this was a particular section of code where Mike’s style was a bit hard to decipher. No offense, Mike, but honestly, wow *sweat*. Let me hasten to clarify that the code wasn’t actually bad, just confusing. Confusing because of sections like this:

i := BSR((s + 1), 1);
j := trunc(72 / i);
z := round(round(exp2((s + 8) / 3)) / i);

Which in C was translated to:

uint32_t i = (s + 1) >> 1,
         j = 72 / i,
         z = lround(exp2((s + 8) / 3) / i);

That was an example where the translation was mostly one-to-one, save for BSR() being >> and trunc() not being needed at all, and one of the round()s being detrimental to the calculation… see how even the simplest-seeming things proliferate? Then there was the calculation of the angle from the player’s current position to the warp destination. In Pascal code that was a lot of fun with FixRatio() and AngleFromSlope() and various manual additions and subtractions of 180 and divisions by 10 and what have you. In C, because I chose to store the current player’s angle in a different form than Mike (I store the actual angle in degrees, whereas he stored an index into the set of 35 ship sprites – which was appropos at the time), I got to do some magic with atan2():

double          dx = d.x - pos.x,
                dy = d.y - pos.y,
                theta = atan2(-dy, dx), theta_deg = round(fma(theta, 180.0 / M_PI, 360.0 * signbit(theta)));

And that just gives me the angle from the player’s current position to the warp destination (nor is this the exact code; there are even more calculations done to get the correct coordinate values that aren’t necessary to this discussion); from there I have to calculate the difference between that and the player’s current facing and turn one increment per “tick” of the game timer to eventually reach the correct facing. Those of you who remember the original game (or have been playing it in SheepShaver, which actually emulates it damn near flawlessly if you run it with a NewWorld ROM and OS 9.0.4) will remember that the ship tends to oscillate back and forth between two facing angles during a warp jump, as there are only 36 sprites, meaning the angle the ship needs to be traveling almost never corresponds to a particular sprite. More multiplies and divides by 10, but there I got a break; the code to handle that was already implemented in the ship navigation subsystem, which handles the turn left and turn right keys. I passed the necessary numbers over to that and it did the job for me.

I was not able to pass off the responsibility of moving the ship to the ship engine subsystem (which handles forward and reverse thrust, as well as full stop), as that code carefully limits the player’s maximum speed for impulse drive. Also, the warp drive has to do some different management of non-maximum speeds; in the end it was better to reimplement it in the warp drive subsystem. The warp drive does, however, rely on the impulse engines to drop out of warp, by requesting a full stop. This had the rather neat side effect of automatically disabling the impulse drive’s user responses while warp was active, without me having to check for that anywhere in the impulse code.

Oh, and the emergency warp drive also works.

But enough about the warp drive. I’ve also got the energy capcaitor (remember? that green bar telling you you’re gonna die ’cause you used up too much power just getting where you were going and had nothing left to charge your lasers with when you got there?) going. The navigation (again, turn left and right) system is now separate from the impulse drive and can take individual damage. Yes that’s right, in version 3.0 of Missions, the turn thrusters can start to die just like everything else, although I was lenient and gave them very low hit-to-damage ratios. Speaking of which, the damage system is implemented too; ship’s systems can now take damage and lose functionality, though right now there’s nothing that does damage to them. Obviously to do the warp drive I had to upgrade the long range scanners, so those are now even closer to fully functional.

Oh, and I also made the “lights” draw exactly correctly at last. They weren’t quite right before.

Yay progress!

I’m very tired, so I don’t have the oomph to do all the fancy stuff I usually do in one of these posts, sorry guys. Quick list of things that’ve gotten done:

1. The long range and sector scans are complete.
2. The viewscreen displays planets and their stars.
3. The little scrolling red thing under the viewscreen (“lights”) is working.
4. A whole long list of off-by-a-few pixel errors is now fixed.
5. I went through all the images and fixed the color correction profiles, now it actually looks like the old game.
6. The sound toggle works!

As usual, there’s lots of infrastructure behind what seem like minor interface changes. The speed of things will tend towards increase, not decrease. Thanks to all who keep up with this; I appreciate your faith in me, not to mention the attention :-).

Skip the roleplay blurb

Ah, the sweet scent of progress. I’ve made a build that makes the starfield appear in the viewscreen, and to test the star scrolling I made the arrow keys move it around. Not exactly a playable game quite yet, but now there’s actually a game screen to be had. Behind the starfield of that viewscreen, there’s planets and starbases and crew and cargo all set up and just waiting to be displayed. Still need to tweak the starfield generation to be a little more evenly distributed, but that’s a detail. Here’s a screenshot for you, enjoy and drool.

Missions of the Reliant viewscreen shot

Alliance Headquarters
Stardate 2310.14179785535022

I’ve accomplished surprisingly little in the last couple of days, in functional terms. I can sum up why pretty easily: I’ve had to stop and puzzle out exactly how Michael did some of the things in his code. Player velocity, especially, is giving me grief.

This isn’t Michael’s fault. He didn’t write obscure code (well, a little…) or implement anything stupidly. The problem was his confinement to old Mac Toolbox APIs in Pascal. One does not simply toss around floating-point math in System 7. (Nor does one simply walk into Mordor, but that’s another story.) Pascal had a floating-point type (REAL), but in those days it was slower than my brain on a Monday morning. I’m not sure why, since almost every Mac since the Mac II had a MC68881 or better FPU, but we were always told to use the FixMath package for efficiency just the same. So we used fixed point types and did fun little things like this:

integerPart := trunc(Fix2X(fixedValue));
fractionPart := fixedValue - Long2Fix(integerPart);

With math like that, and manual compensation for overflow going on, I think I can be forgiven for having to stare blindly at the uncommented code for about two hours before it finally made sense to me. It’s been quite a few years since I’ve worked without native floating-point, and a lot of that time was spent dredging up the memories. 21 lines of Michael’s Pascal code, all of them necessary in the environment it was written for, boil down to a single line in modern C, and in fact a single assembly language instruction too if you care to look at things at that level. In these days of multimedia CPU extensions, if I thought it were necessary for performance I could write it such that all the calculations for all the game objects that needed to move around were done in one vector instruction (SIMD add). I don’t think it’s necessary, but the fact that I could is a sign of just how much CPUs have changed. It’s also a tribute to all those people who did it the hard way 15 years ago.

Other progress includes implementation of the sector object map (meaning planets and starbases, and their locations), reconversion of the rather broken SapirSans font (just opening it in Font Book made ATSUI whine quite loudly, and the italic variant was progmatically indistinguishable from the plain one) into a correctly-formed font suitcase by the very helpful if cryptic FontForge font editor program, and cargo, personnel, and crew management code. As usual, all of this stuff is backend and not visible in a build yet, so I have no screenshots to show. I will soon, though; now that I’ve figured out how the player moves around I can at least make the viewscreen work. Stay tuned.

P.S.: If there’s anyone who follows and enjoys the little roleplay blurbs, speak up in a comment and I’ll continue them. It only takes one voice!

Alliance Headquarters
Stardate 2310.13816640048673

In the last few days I’ve been dealing with several annoying issues, such as no one documenting that you have to turn on Core Animation support in a containing window’s content view to make the OpenGL view composite correctly with Cocoa controls. Four hours wasted on one checkbox. Sigh.

Still, there’s some progress to be had.

1. The loading bar now displays and loads all the various data needed.
2. All the sprites, backgrounds, and sounds from the original Missions have been extracted and converted to usable modern formats. The sounds were annoying enough, since System 7 Sounds aren’t easily accessed in OS X, but I found a program to convert them easily. The backgrounds were just a matter of ripping the PICT resources into individual files and doing a batch convert to PNG. The sprites… those were a problem. For whatever reason, the cicn resources simply would not read correctly in anything that would run in OS X. Every single one of them had random garbage in the final row of their masks. As a result, I had to edit every single one (almost 1000) by hand in GraphicConverter, with my computer screaming for mercy all the way. Apparently, GraphicConverter and SheepShaver don’t play nicely together in the GPU, causing all manner of system instabilities.
3. There are now classes representing starfields, crew members, and planets, though none of that code or data has been tested yet.
4. I’m now building with PLBlocks GCC instead of Clang. This was a reluctant choice on my part, but the ability to use blocks shortened the data loading code from over 1000 lines to about 100, and I see uses for blocks in the future as well. Pity the Clang that comes with 10.6 refuses to work correctly with files using blocks and the 10.5 SDK.
5. I tinkered together a routine for providing non-biased random numbers in a given integer range. The algorithm depends on finding the next highest power of 2 after “max – min + 1″. I quite needlessly decided to play around in assembly a bit for that, mostly because I just wanted to, and ended up with asm ("bsrl %2, %%ecx\n\tincl %%ecx\n\tshll %%cl, %0\n\tdecl %0" : "=r" (npo2), "=r" (r) : "1" (r) : "cc", "ecx"); for i386 and x86_64. I fall back on a pure-C approach for PPC compilation. I haven’t benchmarked this in any way, and I know for a fact that doing so would be meaningless (as the arc4random() call is inevitably far slower than either approach). It was mostly an exercise in knowing assembly language.
6. The “new game” screen, where the scenario and difficulty are selected, now exists. That was also interesting, as it involved shoving a Cocoa view on top of an OpenGL view. I can use that experience for all the other dialogs in the game.

As always, more updates will be posted as they become available.

Alliance Headquarters
Stardate 2310.12630998555023

Progress today was unfortunately small, interrupted by a sudden power outage and further stalled by an Internet service that refused to be restored, but here’s the usual list of what was accomplished.

1. Cleaned up the code a bit more
2. Made the main menu buttons draw and interact. Mostly, anyway; they highlight for mouse clicks and key presses, but they don’t do anything else yet.

Yep, that’s all *shame*. I suspect I’ll have better luck tomorrow.

Alliance Headquarters
Stardate 2310.11526541942353

P.S.: Neither the gibberish in the report nor the numbers in the signature are random. A copy of the latest build will be sent to the first person to correctly guess what either of them actually mean in a comment on this blog.

“For all we know, at this very moment, somewhere far beyond all those distant stars, Benny Russell is dreaming of us.” – Avery Brooks as Benjamin Sisko, Star Trek: Deep Space 9, “Far Beyond the Stars”.

Working on Missions at the level I am so far, I feel about that far away from the game’s universe. Still, there’s been a bit of progress today.

1. First off, I went to grab the main screen out of the original Missions. This time I didn’t have to play around with PICT resources (I did anyway, but that’s besides the point). There was a nice non-composited Photoshop document sitting around with all its individual layers to play with. I tore into it with a vengeance – poor file. In the end, I didn’t do much, just added my copyright to Michael’s and erased the UI buttons.
   
   Erased the UI buttons?
   
   Well, yes. Having looked through the old code, Michael had used QuickDraw as it was meant to be used and been drawing the user interaction with the buttons by writing over the bitmap data with DrawString(). An time-honored and venerable way of doing things in the Mac Toolbox, but not at all suited to efficiency in an OpenGL application. Wiping out the buttons was the first step in separating them out entirely for compositing as OpenGL textures. Probably overkill anyway in the end, but keep in mind this is a learning experience for me and I figured I’d use the general code instead of special-casing this screen more than necessary.
2. Once I had the main screen image re-composited into a nice PNG (bye-bye PICT!), I plugged that into glTexImage2D() and voila, the main screen now displayed in the window! Of course, that screen was bereft of all the nice details that make Missions what it is, so I set about adding the little touches back in. The most obvious of these was the version number in the lower-right corner of the screen. It took me a while to figure out how to get the arcane combination of string drawing in NSImage and writing into an OpenGL texture object correct, but I got there in the end thanks to a little timely help. Incompatible coordinate systems and swapped RGBA/BGRA component ordering were the order of that couple of hours. Whew. A few calls to -[NSBundle objectForInfoDictionaryKey:] and several searches online for versions of the embedded fonts that worked properly later, I had the version number composited neatly on top of the background. Progress!
3. Of course, the code was a disaster at this point. I’d gone through so many dozen iterations of fixing my snafus… well, long story short, I took some time out to reorganize, and got my texture loading and sprite management all neatly separated into their respective classes, including having the sprite class (replacing Michael’s use of SAT in the original code) do the necessary coordinate transformation so I could use the numbers from the original code cleanly. Not to mention some carefully managed global constants to hold useful values, such as references to the fonts and custom colors being used.

And here’s the reward of all that hard work:

First draft of the Missions of the Reliant main screen

I know it doesn’t look like much, but as with all programming, it’s the infrastructure behind it that counts. It’s something most users never see and don’t realize the sheer difficulty of maintaining, but it’s there and it’s important. With all that structure in place, once I’ve gotten some sleep I can make much faster progress tomorrow.

Stay tuned for further updates.

Alliance Headquarters
Stardate 2310.11299452429843

Well, having the project file for Missions in place, I went to organize some of the resources – sprites, backgrounds, strings, all that fun jazz, and there’s plenty of it. In particular, I found myself re-engineering a couple of icons to support the much larger icon sizes we’ve gotten in Mac OS since the ancient days – 8-bit 32×32 icons are well and good, but how’s a 32-bit 512×512 snapshot with alpha channel sound? Pretty good? I thought so. A couple hours tweaking around in GraphicConverter and Photoshop Elements later, I had a nice large icon for the application and saved games. Of course I kept the original icon for 32×32 and 16×16 sizes.

One might ask, what the heck was I doing playing around with graphics when there’s so much code to write? There are two answers. One, that’s just the way I work: Once I get it into my head to finish a task, I get a bit exclusive about it. Two, it was fun, and a part of adding the tiny little bits of personal touch to the port. I wouldn’t want to detract from Michael’s work, of course, but at the same time I am putting in quite a bit of effort to bring that work to the modern audience, so I see no reason that effort can’t be remotely noticable.

Of course, most of the original graphics were vector models done in an old program called Infini-D. Unfortunately, I can’t find this program or anything which can read its format…

Having finished poking around in Photoshop Elements, I went to look up the fundamentals of OpenGL 2D on Mac OS X. Four hours of playing around with CGImage, NSOpenGLView, and glTexImage2D later, I figured out why the alpha channel in the PNG I was using to test was being completely ignored: I never called glEnable(GL_BLEND);. Egg on face much? Oh well. At least I finally made it work. I now have a basic setup in place with which to draw sprites and backgrounds in the game window. Not bad for a few hours and not having done OpenGL in five years, if you ask me.

At least I was vindicated in thinking NSOpenGLView had to be at least a little bit useful despite loud claims by OpenGL coders that I might as well resign myself to subclassing NSView and doing the setup by hand!

That’s about it for today. I’d like, however, to share this amusingly useful little macro with my fellow Objective-C users who aren’t in GC-land yet. I wanted a nice compact way to add a Core Foundation object to an NSAutoreleasePool without doing lots of ugly typecasts. The result was this:

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#define CFAutorelease(cftyp)        ((typeof((cftyp)))[((id)(cftyp)) autorelease])

Nothing like cheating a bit with typeof(); despite appearances, the expression is not evaluated twice! That let me write bits like CGColorSpaceRef colorSpace = CFAutorelease(CGColorSpaceCreateDeviceRGB()); instead of CGColorSpaceRef colorSpace = (CGColorSpaceRef)[(id)CGColorSpaceCreateDeviceRGB() autorelease];. Much more readable, IMHO. The fact that sending autorelease to nil/NULL does nothing and returns NULL is just a lovely little bonus. This doesn’t work quite right in GC code, of course, so don’t try it there.

The other thing that made me happy was thumbing my nose at all the “ARB_texture_rectangle is so useless” noise. Sure, if you’re doing fancy 3D drawing, a texture with non-parameterized coordinates and no non-clamp wrapping and no mipmaps or borders is a problem. Not so much in simple 2D. Why complicate backwards compatibility by using ARB_texture_non_power_of_two?

Yes, I am a woman. And I’m 27. And I’m a programmer.

That is all.

“Anything that happens, happens. Anything that, in happening, causes something else to happen, causes something else to happen. Anything that, in happening, causes itself to happen again, happens again.

It doesn’t necessarily do it in chronological order, though.” – Mostly Harmless, Douglas Adams.

Those who have been using Macs for at least 14 years may or may not remember a space game for old Macs that went by the name “Missions of the Reliant”.

It was a really fun little game with a few missions in it, changable crew members in your ship, powerups for your ship, a nice big galaxy to hang around in, systems that took damage and could be repaired… if you’re thinking Rescue!, don’t, Missions was much better.

Anyway, like all the old Mac games, it’s long since nonfunctional on modern machines. But I wasn’t willing to settle for that, so I pulled up my e-mail and wrote a letter to Michael Rubin, the original author of Missions, asking if I might get the source code and take a crack at porting it to OS X.

His enthusiasm was beyond anything I could have hoped for. I’m very grateful to him for the opportunity he’s given me to bring a classic back to the Mac. I’ll be posting updates here regularly about my progress on the port.

Progress Report 1

Well, I’ve got the code, and I’ve looked it over. Ah, the old glory days of Pascal, inline A-traps, GWorlds, manual event handling… The Mac Toolbox did almost nothing for you; it was a true low-level interface to the OS, something I feel we’ve gotten away from in these days of Cocoa. Sure, OS X has the POSIX interfaces, but they’re a whole different world. Anyway, the code is a real trip back to olden times, and I love every minute of it.

First step was to create the Xcode project. That took about three hours.

Wait, what? Three hours? Well, once you figure setting up the project settings, the target settings, tweaking the things Xcode’s templates don’t get quite right, editing the pregenerated files to not have broken line breaks and incorrect heading comments, and writing the entire Info.plist for the application, that’s a lot of work! I had to look up Info.plist keys, UTI listings, sweep the original source code for the proper value of NSHumanReadableCopyright, and ask a question or two about semantics in the #macdev IRC channel.

Next step, I figure, is to sweep up all the original visual resources – strings, pictures, icons – and reorganize them out of old-style rsrc files into a modern application’s Resources folder. Yes, I’m aware you can still use resource files in OS X, but I feel if you’re going to do something, you might as well do it right!

After that, I have to take a little time out to brush up on my OpenGL 2D, it’s been awhile since I used it and I never did use it for anything this complex. Binding several dozens of textures to represent all the various sprites should be a fascinating undertaking.

I’m enjoying the hell out of myself *grin*. Thanks again, Michael!

Time and time again a thread will come up on the xcode-users mailing list about how to make Xcode put a build number in an application’s Info.plist.

The first answer is always agvtool, but it’s the wrong answer, as agvtool is a version manager for public versions. It’s what generates all those wacky numbers you see in Mac software, such as “Mac OS X Version 10.6.2 Build 10C540″ or “Xcode version 3.2.1 build 1613.0″. It’s certainly not the simple build number people are looking for.

Everyone has their own way of dealing with this, as Xcode makes it extremely difficult to handle it in any elegant way. For example, because Xcode absolutely insists on processing Info.plist before doing anything else in a build (why? why!?), you can’t just plug in a build setting replacement and be done. Various and sundry methods exist, most of which involve either writing the value to the generated Info.plist in the built product or modifying the original Info.plist on every build.

I don’t like those methods, so I came up with one that will work nicely and store the build number as a setting within the project file. Much nicer, IMO, than having to touch your Info.plist file every build and then committing the numbers to your version control system.

1. Add a new Run Script build phase to your project. Place it before all other build phases if you want the number to increase for all builds, or after if you want it only to increase on successful builds.
2. Make sure “Run script only when installing” is shut off.
3. Enter “/usr/bin/osascript” as the Shell for the script.
4. Enter this script:

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   tell application "Xcode" set prj to system attribute "PROJECT_NAME" repeat with config in build configurations of project prj try set x to build setting "CURRENT_PROJECT_VERSION" of config set value of x to ((((value of x) as number) + 1) as string) on error set value of build setting "CURRENT_PROJECT_VERSION" of config to "1" end try end repeat end tell set srcrt to system attribute "SRCROOT" set iplstf to system attribute "INFOPLIST_FILE" do shell script "touch " & srcrt & "/" & iplstf

5. In your Info.plist file, add or set a key like this:

   1 2	<key>CFBundleVersion</key> <string>${CURRENT_PROJECT_VERSION}</string>

Figuring out how to make build numbers on a per-target or per-configuration basis is left as an exercise to the reader :-).

P.S. I hate Applescript, but it’s the only way I know of to set build settings in an Xcode project.

I’ve gotten this question once or twice already. I didn’t realize I even had that many readers yet! But the ones I do have don’t seem to get the reference.

Sa souvraya niende misain ye.

The line is written in the Old Tongue language from the excellent Wheel of Time series by the late Robert Jordan, and its exact translation into plain English is “I am lost within my own mind.”

String parsing in C is painful and annoying.

I want to parse the components of an absolute POSIX path. Here’s the code to do it in several languages.

Ah, the wonderful world of the command line. I wouldn’t be able to look at myself in the mirror (and by mirror, I mean reflection in my monitor) if I couldn’t play the shell as if it were a finely tuned 128-key instrument. But I like to add a little pizzaz to the very black-and-white (or black-and-amber, or black-and-green) world of Terminal.

To do this, one adds ANSI color codes to things. Pass a proper flag or two to ls, set CLICOLOR in your environment, and most of all, set your PS1 to something interesting. Here’s mine for my local machine:

PS1='\[\033[35m\]\u@\h\[\033[00m\]:\[\033[94m\]\w\[\033[96m\]\$\[\033[00m\] '

The result looks something like this:

While in the process of working on the WordPress plugin mentioned in my last post, I found myself having to do a edit/save/upload cycle annoyingly often, as this WordPress install doesn’t run on my local machine and I didn’t feel like dealing with getting httpd up and running here again. More than once I caught myself trying to figure out why my changes weren’t having an effect until I realized I was forgetting the upload step. And entering a passphrase for scp every time I hit Save is tedious at best. But this blog is hosted on DreamHost, and TextMate doesn’t have SFTP support, so I couldn’t just mount a network drive in the Finder.

But I’d heard of this magical, wonderful thing called sshfs that would let me mount an sftp server as a volume on my machine. That would solve a lot of problems! At first I did the obvious: I went to Terminal and entered sudo port install macfuse sshfs. It didn’t work. Small wonder; the last version of MacFUSE in MacPorts is 2.0.3, which is a considerable distance behind the most recent release, 2.1.5). So I used the MacFUSE prefpane to update to 2.1.5, but then the sshfs install wanted nothing to do with me because it was built against the older version. I went to download a prebuilt binary, since that was just easier, but there wasn’t one for Snow Leopard. I tried to build sshfs from source, but the prefpane hadn’t installed sufficient libraries to do that with. So I went to build MacFUSE itself from source.

So I was playing around with the rather nice SyntaxHighlighter WordPress plugin. It worked pretty nicely. But it had some issues, IMO:

1. It repurposes the class attribute to act like a pseudo-CSS ruleset with custom rules. To me that’s just ugly.
2. It does all its work client-side. For some things that’s a nice touch, but for a blog with mostly static content it’s wasted time.
3. It does almost everything in JavaScript. I have a personal distaste of working with JavaScript for no especial reason whatosever.
4. It’s LGPLv3. I prefer less restrictive licenses for OSS.

On the other hand, I know the Pygments syntax highlighter pretty well, and I already had a written style plugin for it to get the syntax coloring I like. But there’s no mature Pygments plugin for WordPress that I could find. So I did what any good programmer would do and set out to write my own. I have the working knowledge of PHP (I’m a core dev, for mercy’s sake) and Python to do it with, after all. Not so much WordPress’ plugin API, though, so I took the SyntaxHighlighter plugin as a starting point.

So I was looking at the macro used to calculate 16-bit parity in pure C without branching:

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#define parity(v)   ({ \
        uint16_t pv = (v); \
        pv ^= (uint16_t)(pv < < 8); \
        pv ^= (uint16_t)(pv << 4); \
        pv ^= (uint16_t)(pv << 2); \
        pv ^= (uint16_t)(pv << 1); \
        (uint16_t)(pv & 0x0001); \
    })

It uses GCC’s handy compound statement syntax, but otherwise it’s plain old C. Let’s look at the 64-bit ASM this compiles to at -Os: (more…)

Given this code:

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- (void)calculateData:(int32_t)n intoLeftBuffer:(int16_t *)lbuf rightBuffer:(int16_t *)rbuf
{
    static uint64_t            (*calculateInternalCall)(id, SEL) = NULL;

    if (!calculateInternalCall)
        calculateInternalCall = (uint64_t (*)(id, SEL))[self methodForSelector:@selector(calculateInternal)];
    
    uint64_t    leftEnableMask = self.isEnabled && lbuf ?
                          ((-(is0Enabled & leftEnabled[0])) & 0xFFFF000000000000) |
                          ((-(is1Enabled & leftEnabled[1])) & 0x0000FFFF00000000) |
                          ((-(is2Enabled & leftEnabled[2])) & 0x00000000FFFF0000) |
                          ((-(is3Enabled & leftEnabled[3])) & 0x000000000000FFFF)
                      : 0,
                rightEnableMask = self.isEnabled && rbuf ?
                          ((-(is0Enabled & rightEnabled[0])) & 0xFFFF000000000000) |
                          ((-(is1Enabled & rightEnabled[1])) & 0x0000FFFF00000000) |
                          ((-(is2Enabled & rightEnabled[2])) & 0x00000000FFFF0000) |
                          ((-(is3Enabled & rightEnabled[3])) & 0x000000000000FFFF)
                : 0;

    for (int32_t i = 0; i < n; ++i)
    {
        uint64_t     data = calculateInternalCall(self, @selector(calculateInternal)),
                     lv = data & leftEnableMask, rv = data & rightEnableMask;
        int16_t      *l = (int16_t *)&lv, *r = (int16_t *)&rv;
        lbuf[i] += l[0] + l[1] + l[2] + l[3];
        rbuf[i] += r[0] + r[1] + r[2] + r[3];
    }
}

Where are the two NULL dereferences Clang claims to have found?

We all make mistakes when coding, and some of them are quite deeply foolish. But this particular snafu I just made takes the cake, in my opinion (dumbed-down code):

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// Written as a static inline C function for max
// speed; this is called in a very tight loop, usually
// at something like 40,000 times per second.
static inline uint8_t _readByte(NSUIntger *cursor,
                                const char *bytes,
                                NSUInteger maxlen)
{ return (*cursor < maxlen) ? bytes[*cursor++] : 0x66; }
// Macro for readability, known to be called only from the one function
#define readByte() _readByte(&cursor, buffer, bufferlen)
// Macro to skip so many bytes
#define skipBytes(n) do { \
    __typeof__(n) nn = (n); \
    for (uint8_t i = 0; i < nn; ++i) \
        readByte(); \
    } while (0)
- (void)processBuffer
{
    // assume the declarations of n, cursor, buffer, bufferlen
    // ...
    n = readByte();
    // ...
    else if (n > 0x29)
        skipBytes((uint8_t[16]){0,0,0,1,1,2,0,0,0,0,2,2,3,3,4,4})(n & 0xF0) >> 4);
}

See it? (Hint: Look at the implementation of skipBytes().)