Eval Expression is a Mac OS X service to evaluate the selected text of any text field as a Ruby expression. My instinct was to choose Perl, however Ruby offers binary in addition to decimal, hex and octal numerical literals. The service becomes infinitely more useful if you assign it a global shortcut in Keyboard preferences. In my case I assigned a combination that seemed obvious, ⌘= It came about as I was working on some layout in Xcode 4 / Interface Builder, and needed to adjust the Y position of a view by a specific number of units. I’m lazy, and figured the computer should do the work, so I typed 768-35 and tabbed out. Unlike Acorn and Opacity, which evaluates the expression in numerical entries automatically, Xcode simply complained. Not happy, I created this service and it works like a charm. Some examples: ...

I like to reuse the same private keys when generating a signing request to renew my Apple developer certificates. Unfortunately you can’t do this with Keychain Access, as it won’t save the signing request file after you step through the wizard. OpenSSL is your friend. Open Keychain Access, RMB on the key your wish to use and click Export “[Key Name]”. Save it as a .p12 file with a strong password. In my case it was StuartCarnie.p12. ...

Update: Added iPhone 5. Update: Added iPhone 4s, iPad 3rd gen. Update: Added iPhone 4, iPad 1st gen. I follow the excellent weekly posts by Mike Ash, and entered a brief discussion in comments about toll free bridging. In particular, the difference between calling a method via Objective-C (objc_msgSend) and it’s equivalent CoreFoundation C call. Mike suggested adding it to his original suite of tests, which lead to the following results. iPhone 5 (-mno-thumb) Custom Apple A6 ARM Cortex A15, up to 1.2GHz Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 0.3 3.1 C++ virtual method call 100000000 0.3 3.3 Integer division 100000000 1.1 10.9 Objective-C message send 100000000 1.4 13.7 Float division with int conversion 10000000 0.2 24.7 Floating-point division 100000000 2.5 24.8 Objective-C objectAtIndex: 10000000 0.4 35.9 CF CFArrayGetValueAtIndex 10000000 0.5 50.9 16 byte memcpy 10000000 0.7 65.8 16 byte malloc/free 10000000 4.8 482.7 NSAutoreleasePool alloc/init/release 100000 0.1 533.4 NSObject alloc/init/release 100000 0.1 1169.0 NSInvocation message send 100000 0.1 1391.8 16MB malloc/free 1000 0.0 13331.8 Zero-second delayed perform 1000 0.1 99329.1 pthread create/join 100 0.0 120390.0 1MB memcpy 100 0.0 421517.1 iPhone 5 (thumb) Custom Apple A6 ARM Cortex A15, up to 1.2GHz Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 0.3 3.1 C++ virtual method call 100000000 0.4 4.0 Integer division 100000000 1.1 10.8 Objective-C message send 100000000 1.4 13.6 Float division with int conversion 10000000 0.2 24.9 Floating-point division 100000000 2.6 26.4 Objective-C objectAtIndex: 10000000 0.4 35.6 CF CFArrayGetValueAtIndex 10000000 0.5 51.0 16 byte memcpy 10000000 0.7 65.8 16 byte malloc/free 10000000 4.7 474.3 NSAutoreleasePool alloc/init/release 100000 0.1 513.2 NSObject alloc/init/release 100000 0.1 1183.1 NSInvocation message send 100000 0.1 1241.5 16MB malloc/free 1000 0.0 12979.7 Zero-second delayed perform 1000 0.1 83574.5 pthread create/join 100 0.0 121289.2 1MB memcpy 100 0.0 426971.7 iPad 3 (thumb) Apple A5x ARM Cortex A9 1000MHz Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 1.1 11.5 C++ virtual method call 100000000 1.3 12.7 Floating-point division 100000000 2.6 26.1 16 byte memcpy 10000000 0.3 26.2 Float division with int conversion 10000000 0.3 26.3 Integer division 100000000 2.9 28.7 Objective-C message send 100000000 3.6 35.5 Objective-C objectAtIndex: 10000000 0.7 69.0 CF CFArrayGetValueAtIndex 10000000 1.3 131.7 16 byte malloc/free 10000000 4.3 433.9 NSAutoreleasePool alloc/init/release 100000 0.1 600.2 NSObject alloc/init/release 100000 0.1 1235.4 NSInvocation message send 100000 0.3 2966.6 16MB malloc/free 1000 0.0 11633.0 Zero-second delayed perform 1000 0.1 121336.0 pthread create/join 100 0.0 130293.3 1MB memcpy 100 0.2 1662780.4 iPad 3 (-mno-thumb) Apple A5x ARM Cortex A9 1000MHz Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 0.9 9.0 C++ virtual method call 100000000 1.1 11.1 Integer division 100000000 2.4 24.1 Floating-point division 100000000 2.6 26.1 Float division with int conversion 10000000 0.3 26.1 16 byte memcpy 10000000 0.3 27.1 Objective-C message send 100000000 2.7 27.2 Objective-C objectAtIndex: 10000000 0.7 68.4 CF CFArrayGetValueAtIndex 10000000 1.0 103.3 16 byte malloc/free 10000000 4.3 432.5 NSAutoreleasePool alloc/init/release 100000 0.1 570.4 NSObject alloc/init/release 100000 0.1 1209.9 NSInvocation message send 100000 0.2 1682.2 16MB malloc/free 1000 0.0 10251.2 pthread create/join 100 0.0 118494.2 Zero-second delayed perform 1000 0.1 121578.2 1MB memcpy 100 0.2 1635983.3 iPhone 4s (thumb) Apple A5 ARM Cortex A9 ~800MHz Name Iterations Total time (sec) Time per (ns) C++ virtual method call 100000000 1.1 11.3 IMP-cached message send 100000000 1.3 12.6 Integer division 100000000 3.1 31.4 Float division with int conversion 10000000 0.3 32.6 Floating-point division 100000000 3.3 32.6 16 byte memcpy 10000000 0.3 32.6 Objective-C message send 100000000 3.4 33.8 Objective-C objectAtIndex: 10000000 0.9 85.9 CF CFArrayGetValueAtIndex 10000000 1.6 165.0 16 byte malloc/free 10000000 5.4 542.2 NSAutoreleasePool alloc/init/release 100000 0.1 753.2 NSObject alloc/init/release 100000 0.2 1511.7 NSInvocation message send 100000 0.2 2111.9 16MB malloc/free 1000 0.0 19033.7 pthread create/join 100 0.0 142817.5 Zero-second delayed perform 1000 0.1 146302.7 1MB memcpy 100 0.2 1787482.1 iPhone 4 (-fthumb) Apple A4 ARM Cortex A8 ~800MHz Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 0.9 9.0 C++ virtual method call 100000000 1.0 10.2 16 byte memcpy 10000000 0.4 36.2 Integer division 100000000 4.1 40.6 Objective-C message send 100000000 4.1 40.8 Floating-point division 10000000 0.9 89.4 Objective-C objectAtIndex: 10000000 1.1 105.8 Float division with int conversion 10000000 1.1 105.8 CF CFArrayGetValueAtIndex 10000000 1.7 168.1 NSInvocation message send 100000 0.1 550.8 16 byte malloc/free 10000000 6.6 656.3 NSAutoreleasePool alloc/init/release 100000 0.1 979.5 NSObject alloc/init/release 100000 0.4 4277.9 16MB malloc/free 1000 0.0 20406.7 pthread create/join 100 0.0 139971.2 Zero-second delayed perform 1000 0.2 243883.3 1MB memcpy 100 0.1 1150657.9 iPhone 3GS (-fthumb) ARM Cortex A8 ~600MHz / 1.66 ns per cycle Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 1.2 11.7 C++ virtual method call 100000000 1.3 13.5 16 byte memcpy 10000000 0.5 46.0 Objective-C message send 100000000 5.4 53.9 Integer division 100000000 6.3 62.9 Floating-point division 10000000 1.2 117.4 Float division with int conversion 10000000 1.4 138.2 Objective-C objectAtIndex: 10000000 1.4 140.1 CF CFArrayGetValueAtIndex 10000000 2.2 220.0 16 byte malloc/free 10000000 6.4 642.6 NSInvocation message send 100000 0.1 723.0 NSAutoreleasePool alloc/init/release 100000 0.1 1305.9 NSObject alloc/init/release 100000 0.6 5743.7 16MB malloc/free 1000 0.0 16104.0 pthread create/join 100 0.0 185759.2 Zero-second delayed perform 1000 0.4 353519.4 1MB memcpy 100 0.2 2170179.2 iPhone 3GS (no thumb) ARM Cortex A8 ~600MHz / 1.66 ns per cycle Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 1.2 11.8 C++ virtual method call 100000000 4.3 42.9 Objective-C message send 100000000 5.9 59.2 CF CFArrayGetValueAtIndex 10000000 1.0 97.9 Integer division 100000000 9.8 98.4 16 byte memcpy 10000000 1.1 109.3 Floating-point division 10000000 1.2 118.5 Objective-C objectAtIndex: 10000000 1.3 129.0 Float division with int conversion 10000000 1.4 142.6 16 byte malloc/free 10000000 7.5 748.6 NSInvocation message send 100000 0.1 806.0 NSObject alloc/init/release 100000 0.5 4793.1 NSAutoreleasePool alloc/init/release 100000 0.5 4953.1 16MB malloc/free 1000 0.0 17969.2 Zero-second delayed perform 1000 0.2 211840.4 pthread create/join 100 0.0 214742.5 1MB memcpy 100 0.3 3162774.6 iPhone 3G ARM1176 ~412MHz / 2.4ns per cycle Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 3.9 38.6 C++ virtual method call 100000000 5.0 49.9 Floating-point division 10000000 0.8 81.3 Float division with int conversion 10000000 0.8 81.4 16 byte memcpy 10000000 1.4 136.0 Objective-C message send 100000000 14.9 148.6 Integer division 100000000 16.2 162.2 CF CFArrayGetValueAtIndex 10000000 2.0 201.7 Objective-C objectAtIndex: 10000000 4.2 418.3 NSInvocation message send 100000 0.2 1833.2 16 byte malloc/free 10000000 27.3 2729.8 NSObject alloc/init/release 100000 1.4 14179.1 NSAutoreleasePool alloc/init/release 100000 1.9 18956.7 16MB malloc/free 1000 0.0 47811.3 Zero-second delayed perform 1000 0.8 803419.3 pthread create/join 100 0.1 1085830.0 1MB memcpy 100 1.0 9902796.7 iPad (-fthumb) Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 0.7 7.1 C++ virtual method call 100000000 0.8 8.1 16 byte memcpy 10000000 0.3 27.7 Objective-C message send 100000000 3.2 32.3 Integer division 100000000 3.4 33.7 CF CFArrayGetValueAtIndex 10000000 0.6 58.8 Floating-point division 10000000 0.7 70.5 Objective-C objectAtIndex: 10000000 0.8 81.6 Float division with int conversion 10000000 0.8 83.1 16 byte malloc/free 10000000 3.6 357.8 NSInvocation message send 100000 0.0 470.8 NSAutoreleasePool alloc/init/release 100000 0.3 2957.0 NSObject alloc/init/release 100000 0.3 3080.2 16MB malloc/free 1000 0.0 14824.2 pthread create/join 100 0.0 127386.2 Zero-second delayed perform 1000 0.2 225271.3 1MB memcpy 100 0.1 1064566.2 iPad (-mno-thumb) Apple A4 ARM Cortex A8 ~1GHz / 1 ns per cycle Name Iterations Total time (sec) Time per (ns) IMP-cached message send 100000000 0.8 8.1 C++ virtual method call 100000000 2.2 21.8 16 byte memcpy 10000000 0.3 28.2 Objective-C message send 100000000 3.2 32.5 Integer division 100000000 3.4 33.9 CF CFArrayGetValueAtIndex 10000000 0.6 55.8 Floating-point division 10000000 0.7 70.9 Objective-C objectAtIndex: 10000000 0.8 81.6 Float division with int conversion 10000000 0.8 82.8 16 byte malloc/free 10000000 3.6 358.3 NSInvocation message send 100000 0.0 473.4 NSAutoreleasePool alloc/init/release 100000 0.3 3017.6 NSObject alloc/init/release 100000 0.3 3071.8 16MB malloc/free 1000 0.0 14623.6 pthread create/join 100 0.0 128674.6 Zero-second delayed perform 1000 0.3 255627.5 1MB memcpy 100 0.1 1063407.5 Note that I did reduce the iterations from the original tests, so whilst the total times are significantly less, the iteration times are still a reflection of overall performance. Compared to Mike’s results, these show that the IMP method is indeed faster as expected, but this was only after I changed to a release build. I also compiled these with Thumb disabled unless otherwise specified. I’ve recently watched some iTunes U videos released by Apple on optimizing OpenGL ES 2.0 and a key takeaway was that the Cortext A8 architecture should always be compiled with thumb enabled. The Cortex CPU uses the newer Thumb-2 instruction set, which has native instructions for floating point. The benefit of Thumb is reduced code size and potentially better performance by utilising the I-cache. ...

To make it easier to find the assembly generated when you ‘Show Assembly Code’, embed comments using: asm("# your comment")