Speaking in front of the reconstruction, reconstruction goal is to improve the readability of the code maintainability. The main goal here speak of the code is adjusted for the performance of the software. In many cases, performance, maintainability and readability are conflicting indicators, so before doing code tuning, it must find a good really need? To improve the performance of the software there are many ways, are listed in the following checklist, the code adjustment is a method other methods have had to die before using. In short, caution!
Checklist: Code-the Tuning Strategies,
Overall Program Performance
Have you Considered Improving Performance by Changing at The Program requirements?
Have you Considered Improving Performance by modifying at The Program's Design?
Have you Considered Improving Performance by modifying at The class Design?
Have you Considered Improving Performance by Avoiding Operating Interactions System?
Have you Considered Improving Performance by Avoiding the I / O?
Have you Considered Improving Performance by a using INSTEAD of AN A Compiled Language Interpreted Language?
Have you considered improving performance by using compiler optimizations?
Have you considered improving performance by switching to different hardware?
Have you considered code tuning only as a last resort?
Code-Tuning Approach
Is your program fully correct before you begin code tuning?
Have you measured performance bottlenecks before beginning code tuning?
Have you measured the effect of each code-tuning change?
Have you backed out the code-tuning changes that didn't produce the intended improvement?
Have you tried more than one change to improve performance of each bottleneck, i.e., iterated?
It will have reason to exist, since the total in some cases we had to use the code changes, he should know about some of the techniques used in time. The first thing to do is to measure. Good performance is not good, how fast, light-guessing is not enough, we must measure to know; how to adjust the effect, and only measure to know. Therefore, the measure is the first step. According to the famous 80/20 rule, there is always a small part of the code that consumes most of the performance, we need to find that a small part of the code by measuring, then adjust them to optimize.
We have different methods of adjustment, following checklist are listed, not one by one explain the book are reference examples. It should be noted that no matter which method, because the compiler, the language, the environment is different, the result is often unpredictable, so the results of how to adjust the code must be confirmed by measurement. It is also worth mentioning that the code can be adjusted to optimize multi-pronged approach, as better results. But we must note that the more often optimize readability maintainability worse, this trade-off, to what extent be considered good.
Checklist: Code the Tuning Techniques
the Improve Size Both Speed and
Substitute Table Lookups for Complicated Logic
Jam Loops
the Use of Floating-Point Integer Variables INSTEAD
the Initialize Data Time AT the compile
the Use Constants The correct type of
the Precompute Results
the Eliminate Common subexpressions
Translate key routines to assembler
Improve Speed Only
Stop testing when you know the answer
Order tests in case statements and if-then-else chains by frequency
Compare performance of similar logic structures
Use lazy evaluation
Unswitch loops that contain if tests
Unroll loops
Minimize work performed inside loops
Use sentinels in search loops
Put the busiest loop on the inside of nested loops
Reduce the strength of operations performed inside loops
Change multiple-dimension arrays to a single dimension
Minimize array references
Augment data types with indexes
Cache frequently used values
Exploit algebraic identities
Reduce strength in logical and mathematical expressions
Be wary of system routines
Rewrite routines in line
Checklist: Code-the Tuning Strategies,
Overall Program Performance
Have you Considered Improving Performance by Changing at The Program requirements?
Have you Considered Improving Performance by modifying at The Program's Design?
Have you Considered Improving Performance by modifying at The class Design?
Have you Considered Improving Performance by Avoiding Operating Interactions System?
Have you Considered Improving Performance by Avoiding the I / O?
Have you Considered Improving Performance by a using INSTEAD of AN A Compiled Language Interpreted Language?
Have you considered improving performance by using compiler optimizations?
Have you considered improving performance by switching to different hardware?
Have you considered code tuning only as a last resort?
Code-Tuning Approach
Is your program fully correct before you begin code tuning?
Have you measured performance bottlenecks before beginning code tuning?
Have you measured the effect of each code-tuning change?
Have you backed out the code-tuning changes that didn't produce the intended improvement?
Have you tried more than one change to improve performance of each bottleneck, i.e., iterated?
It will have reason to exist, since the total in some cases we had to use the code changes, he should know about some of the techniques used in time. The first thing to do is to measure. Good performance is not good, how fast, light-guessing is not enough, we must measure to know; how to adjust the effect, and only measure to know. Therefore, the measure is the first step. According to the famous 80/20 rule, there is always a small part of the code that consumes most of the performance, we need to find that a small part of the code by measuring, then adjust them to optimize.
We have different methods of adjustment, following checklist are listed, not one by one explain the book are reference examples. It should be noted that no matter which method, because the compiler, the language, the environment is different, the result is often unpredictable, so the results of how to adjust the code must be confirmed by measurement. It is also worth mentioning that the code can be adjusted to optimize multi-pronged approach, as better results. But we must note that the more often optimize readability maintainability worse, this trade-off, to what extent be considered good.
Checklist: Code the Tuning Techniques
the Improve Size Both Speed and
Substitute Table Lookups for Complicated Logic
Jam Loops
the Use of Floating-Point Integer Variables INSTEAD
the Initialize Data Time AT the compile
the Use Constants The correct type of
the Precompute Results
the Eliminate Common subexpressions
Translate key routines to assembler
Improve Speed Only
Stop testing when you know the answer
Order tests in case statements and if-then-else chains by frequency
Compare performance of similar logic structures
Use lazy evaluation
Unswitch loops that contain if tests
Unroll loops
Minimize work performed inside loops
Use sentinels in search loops
Put the busiest loop on the inside of nested loops
Reduce the strength of operations performed inside loops
Change multiple-dimension arrays to a single dimension
Minimize array references
Augment data types with indexes
Cache frequently used values
Exploit algebraic identities
Reduce strength in logical and mathematical expressions
Be wary of system routines
Rewrite routines in line
