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    <p>Maybe the first value is much larger? apart from CoreFoundation's CFNumber caching, the "new" runtime uses tagged pointers, allowing integers within the range of 24 bit to be encoded directly into the pointer - the runtime then figure out it's a tagged pointer by looking at the last bit (and that its a CFNumber by looking at the 3 bits before the last bit and the target number size - 8, 16, 32, 64 bit - using the next 4 bits before). <br/>On a 32-bit system (current iPhones), that means that for ("small") negative 32 bit numbers or large positive numbers, CoreFoundation will allocate an object. For everything else, it uses the following expression that is way faster:</p> <pre><code> case kCFNumberSInt32Type: { int32_t value = *(int32_t *)valuePtr; // this loads the actual numerical value passed to CFNumberCreate() #if !__LP64__ // We don't bother allowing the min 24-bit integer -2^23 to also be fast-pathed; // tell anybody that complains about that to go ... hang. int32_t limit = (1L &lt;&lt; 23); if (value &lt;= -limit || limit &lt;= value) break; #endif uintptr_t ptr_val = ((uintptr_t)((intptr_t)value &lt;&lt; 8) | (2 &lt;&lt; 6) | kCFTaggedObjectID_Integer); return (CFNumberRef)ptr_val; } </code></pre> <p>(note that <code>!__LP64__</code> is true for 32-bit systems)</p> <p>Taken from: <a href="http://www.opensource.apple.com/source/CF/CF-744.12/CFNumber.c" rel="nofollow">http://www.opensource.apple.com/source/CF/CF-744.12/CFNumber.c</a></p> <p><p></p> <p>Also, there is a caching mechanism that prevents a range of numbers from being re-created multiple times, just search for "__CFNumberCache" in the same source file.</p>
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    1. POOptimizing NSNumber numberWithInt:
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    1. USMartin Ullrich
    1. USMartin Ullrich
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    1. COThat was not the scenario at the time of the question being asked. Tagged integers were added in iOS 6 and Mac OSX Lion, thus not an issue in the situation given.
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      1. USRichard J. Ross III
    2. COwe shouldn't make this a personal discussion. i just wanted to add it to this "old" question - according to my information tagged pointers were added to the runtime along with the support for weak references in iOS 5.
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      1. USMartin Ullrich
 

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