Dr. Dobb's Journal - April 2008 - (Page 47)

d04orlov_p5ds 2/13/08 8:56 AM Page 47 GCD computation is easy with C++ templates; see Listing Four. Now you can compute the constants that were defined in Listing Two. Because these constants are derived from m, the parameter to next(max), they are also kept in a traits structure specialized on max; see Listing Five. You don’t just compute rem, last, and gcd, but also determine the dispatch ID, which is used to select one of the three variants of next(max) implementations—actually, next () because m is now a compiletime constant. The NO_LOOP variant is selected when there are no remainder values in the value_t range, and no loop is necessary. Unless a very strange platform is used, m is a power of 2. The RETRY_SAME variant is actually the SimpleRange implementation, and is selected when m and rem are relatively prime, and m cannot be reduced once a random value is rejected. Finally, the REDUCE_MAX variant is selected when m and rem share a common factor, which allows reduction of m—as in the m=684 and rem=340 example discussed previously. Because C++ doesn’t allow partial specialization for member functions, and you need partial specialization on a dispatch ID, a private class Dispatch is used. Because Dispatch is specialized on all three values of dispatch_t, only a declaration is necessary for the nonspecialized template (see Listing Six). Listings Seven and Eight show the straightforward specializations for the NO_LOOP and RETRY_SAME dispatch IDs. Listing Nine shows the REDUCE_MAX specialization, which implements the previously described buckets-based approach, with a small variation—the remainder range is not partitioned into GCD subranges, but instead a modulo GCD value is used. That is, low-order bits of rnd are used instead of the high-order bits. The Greatest Common Divisor algorithm computation is easy with C++ templates HD PHOTO N O W A V A I LA B LE F O R D O W N L O A D I S 4 0 - 6 0 % F A ST E R I N P I C TO O LS . Speed-optimized HD Photo libraries are now available within the PICTools Software Development Kit (SDK). Microsoft’s HD Photo offers higher image quality, greater preservation of data and advanced features for today’s digital imaging applications. It is a still image compression algorithm for continuous tone photographic images and features lossy, as well as lossless, compression, multiple colorspaces, a wide dynamic range, and extensive metadata support. PICTools SDKs contain low-level C libraries offering advanced image compression, decompression, and editing. Maximum code speed has been achieved through algorithm and machine code optimizations. Also available for .NET and ActiveX. Supported across: 32-bit Sun Solaris 32-bit and 64-bit Linux 32-bit and 64-bit Microsoft Windows IBM AIX Mac OS X Evaluation The supplied code (available online; see “Resource Center,” page 5) can be used to estimate the runtime optimization resulting from the use of SmartRange. The theoretical limit is 25 percent off the original runtime: Going down from the expected 2 calls to Contact us for more information. W W W . P E G A S U S I M A G I N G . C O M Pegasus is a registered trademark of Pegasus Imaging Corporation in the United States. The names of actual companies and products mentioned herein may be the trademarks of their respective owners. April 2008 l www.ddj.com l Dr. Dobb’s Journal 47 http://www.pegasusimaging.com http://www.pegasusimaging.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - April 2008

Dr. Dobb's Journal - April 2008 Contents Hmmmm Alia Vox Developer Diaries Dr. Dobb's Excellence in Programming Award Conversations Fast String Search on Multicore Processors The Byzantine Generals Problem Optimizing Math-Intensive Applications with Fixed-Point Arithmetic Random Numbers in a Range Using Generic Programming The Agile Edge Effective Concurrency Swaine's Flames

Dr. Dobb's Journal - April 2008

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