Jump to content United States-English
HP.com Home Products and Services Support and Drivers Solutions How to Buy
» Contact HP
More options
HP.com home
 Fortran 90, Fortran 77, C, aC++: Exemplar Programming Guide

Chapter 8 Programming conventions for optimal code
» 

Technical documentation

Complete book in PDF
» Feedback
Content starts here

 » Table of Contents

 » Glossary

spacerspacerspacer
spacer
spacer
  		 
 

Table of Contents

Aliasing in Fortran
Aliasing in C
ANSI algorithm
Type-safe algorithm
Specifying aliasing modes
Iteration and stop values
Global variables
False cache line sharing
Aligning data to avoid false sharing
Distributing iterations on cache line boundaries
Thread-specific array elements
Scalars sharing a cache line
Working with unaligned arrays
Working with dependences
Floating-point imprecision
Enabling sudden underflow
Invalid subscripts
Misused directives and pragmas
Loop-carried dependences
Reductions
Nondeterminism of parallel execution
Hidden ordered sections
Misused memory classes
Improper dynamic allocations
Incorrect array pointers
Hidden dependences
Triangular loops
Parallelizing the outer loop
Parallelizing the inner loop
Examining the code
Compiler assumptions
Incrementing by zero
Trip counts that may overflow

This chapter discusses coding tips and common optimization problems you may encounter when developing programs for SMP servers and presents some possible solutions.

Optimization can remove instructions, replace them, and change the order in which they execute. In some cases, improper optimizations can cause unexpected or incorrect results or code that slows down at higher optimization levels. In some cases, user error can cause similar problems in code that contains syntactically-correct constructs or directives that are used improperly. If you encounter any of these problems, look for the following possible causes:

  • Aliasing

  • False cache line sharing

  • Floating-point imprecision ( roundoff error)

  • Invalid subscripts

  • Misused directives and pragmas

  • Misused memory classes

  • Triangular loops

  • Compiler assumptions

NOTE: Compilers perform optimizations assuming that the source code being compiled is valid. Optimizations done on source that violates certain ANSI standard rules can cause the compilers to generate incorrect code.


Message-passing programming vs. shared-memory programming
  		 


Aliasing in Fortran  
Printable version
Privacy statement Using this site means you accept its terms Feedback to webmaster
© Hewlett-Packard Development Company, L.P.