Chapter 5.9, Problem 5.8PP

Program Plan Intro

Given C code:

double aprod(double a[], long n)

{

long i;

double x, y, z;

double r = 1;

for(i=0; i<n-2; i+=3)

{

x = a[i];

y = a[i + 1];

z = a[i+2];

r = r*x*y*z;

}

for(;i<n ; i++)

r*=a[i];

return r;

}

Cycles per element (CPE):

• The CPE denotes performance of program that helps in improving code.
• It helps to understand detailed level loop performance for an iterative program.
• It is appropriate for programs that use a repetitive computation.
• The processor’s activity sequencing is controlled by a clock that provides regular signal of some frequency.

Memory aliasing:

• It denotes a case where two pointers might designate to memory location that is same.
• The compiler should assume that unlike pointers might be aliased for safe optimizations.
• The program aspects that could limit chances for a compiler in generating optimized code denote optimization blockers.
• If a compiler is unable to determine whether two pointers might be aliased, it should adopt that either case would be possible.
• The possible optimization set is been limited in this case.