c# ean 13 check Language Python Visual Basic in Visual C#

Encode EAN-13 Supplement 5 in Visual C# Language Python Visual Basic

Language Python Visual Basic
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Straight Time 3.24 6.26
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First Optimization 2.60 0.16
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Second Optimization 2.53 0.31
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This is a good example of theory not holding up very well to practice. The code with reduced strength seems like it should be faster, but it isn t. One possibility is that decrementing a loop by 1 instead of incrementing it by +1 in Visual Basic hurts performance, but you d have to measure that hypothesis to be sure.
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Initialize at Compile Time
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If you re using a named constant or a magic number in a routine call and it s the only argument, that s a clue that you could precompute the number, put it into a constant, and avoid the routine call. The same principle applies to multiplications, divisions, additions, and other operations. I once needed to compute the base-two logarithm of an integer, truncated to the nearest integer. The system didn t have a log-base-two routine, so I wrote my own. The quick and easy approach was to use the fact that
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log(x) = log(x) / log(base) base
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Given this identity, I could write a routine like this one:
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de Complete
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26. Code-Tuning Techniques
Page 26
For details on binding variables 2 to their values, see Section 3 10.6, Binding Time.
CROSS-REFERENCE
C++ Example of a Log-Base-Two 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 Log-Base-Two 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:
Code-Tuned 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 floating-point 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 Log-Base-Two Routine Based on Integers
unsigned int Log2( unsigned int x ) {
de Complete
26. Code-Tuning Techniques
Page 27
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 floating-point 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 so-called transcendental functions are designed for the worst case that is, they convert to double-precision 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 right-shift 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:
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