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c# ean 13 check Language Python Visual Basic in Visual C#
Language Python Visual Basic Generating UPC  13 In Visual C# Using Barcode encoder for VS .NET Control to generate, create EAN13 image in Visual Studio .NET applications. www.OnBarcode.comRead UPC  13 In Visual C# Using Barcode reader for .NET framework Control to read, scan read, scan image in VS .NET applications. www.OnBarcode.comStraight Time 3.24 6.26
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For details on binding variables 2 to their values, see Section 3 10.6, Binding Time.
CROSSREFERENCE
C++ Example of a LogBaseTwo Routine Based on System Routines
unsigned int Log2( unsigned int x ) { return (unsigned int) ( log( x ) / log( 2 ) ); } This routine was really slow, and since the value of log(2) never changed, I replaced log(2) with its computed value, 0.69314718. Then the code looked like this: C++ Example of a LogBaseTwo Routine Based on a System Routine and a Constant
unsigned int Log2( unsigned int x ) { 0 LOG2 is a named constant equal to 0.69314718.
return (unsigned int) ( log( x ) / LOG2 ); } Since log() tends to be an expensive routine, much more expensive than type conversions or division, you d expect that cutting the calls to the log() function by half would cut the time required for the routine by about half. Here are the measured results: CodeTuned Time 5.97 12.3 1.50
Language C++ Java PHP
Straight Time 9.66 17.0 2.45
Time Savings 38% 28% 39% In this case, the educated guess about the relative importance of the division and type conversions and the estimate of 50 percent were pretty close. Considering the predictability of the results described in this chapter, the accuracy of my prediction in this case proves only that even a blind squirrel finds a nut occasionally. Be Wary of System Routines
System routines are expensive and provide accuracy that s often wasted. Typical system math routines, for example, are designed to put an astronaut on the moon within 2 feet of the target. If you don t need that degree of accuracy, you don t need to spend the time to compute it either. In the previous example, the Log2() routine returned an integer value but used a floatingpoint log() routine to compute it. That was overkill for an integer result, so after my first attempt, I wrote a series of integer tests that were perfectly accurate for calculating an integer log . Here s the code: 2 C++ Example of a LogBaseTwo Routine Based on Integers
unsigned int Log2( unsigned int x ) { de Complete
26. CodeTuning Techniques
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if ( x < 2 ) return 0 ; if ( x < 4 ) return 1 ; if ( x < 8 ) return 2 ; if ( x < 16 ) return 3 ; if ( x < 32 ) return 4 ; if ( x < 64 ) return 5 ; if ( x < 128 ) return 6 ; if ( x < 256 ) return 7 ; if ( x < 512 ) return 8 ; if ( x < 1024 ) return 9 ; ... if ( x < 2147483648 ) return 30; return 31 ; } This routine uses integer operations, never converts to floating point, and blows the doors off both floatingpoint versions. Here are the results: CodeTuned Time 0.662 0.882 3.45
Language C++ Java PHP
Straight Time 9.66 17.0 2.45
Time Savings 93% 95% 41% Performance Ratio 15:1 20:1 2:3 Most of the socalled transcendental functions are designed for the worst case that is, they convert to doubleprecision floating point internally even if you give them an integer argument. If you find one in a tight section of code and don t need that much accuracy, give it your immediate attention. Another option is to take advantage of the fact that a rightshift operation is the same as dividing by two. The number of times you can divide a number by two and still have a nonzero value is the same as the log2 of that number. Here s how code based on that observation looks:

