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// CC -64 -LANG:std -LANG:restrict -Ofast -PHASE:clist -IPA=off -IPA:INLINE=off
//
// When compiled with the above options, these are the results on convex:
// func1: 34.6484
// func2: 24.6603
// func3: 17.2822
//
// func1 is a simple C-style loop.
// func2 has the pointers stuck inside a struct. Prefetching no longer occurs.
// func3 has the pointers inside "iterator" structs, and a read is done
// using an inline operator(). This somehow results in the loop
// being unrolled only twice, instead of 4 times.
#include <iostream.h>
#include <sys/resource.h>
// Paste the Timer class in here so you don't have to have Blitz++
class Timer {
public:
Timer()
{
state_ = uninitialized;
}
void start()
{
state_ = running;
t1_ = systemTime();
}
void stop()
{
t2_ = systemTime();
state_ = stopped;
}
/* Compaq cxx compiler in ansi mode cannot print out long double type! */
#if defined(__DECCXX)
double elapsedSeconds()
#else
long double elapsedSeconds()
#endif
{
return t2_ - t1_;
}
private:
Timer(Timer&) { }
void operator=(Timer&) { }
long double systemTime()
{
getrusage(RUSAGE_SELF, &resourceUsage_);
double seconds = resourceUsage_.ru_utime.tv_sec
+ resourceUsage_.ru_stime.tv_sec;
double micros = resourceUsage_.ru_utime.tv_usec
+ resourceUsage_.ru_stime.tv_usec;
return seconds + micros/1.0e6;
}
enum { uninitialized, running, stopped } state_;
struct rusage resourceUsage_;
long double t1_, t2_;
};
// func1: Simple version
void func1(double* restrict x, double* restrict y, double a, int N)
{
for (int i=0; i < N; ++i)
y[i] += a*x[i];
}
// func2: With pointers inside a struct
struct A {
double* restrict x;
double* restrict y;
double a;
int N;
};
void func2(A& z)
{
for (int i=0; i < z.N; ++i)
z.y[i] += z.a * z.x[i];
}
// func3: with very simple "iterators" (the B struct).
struct B {
int q;
double* restrict data;
double operator()(int i)
{ return data[i]; }
};
struct C {
B x;
B y;
double a;
int N;
};
void func3(C& z)
{
for (int i=0; i < z.N; ++i)
z.y.data[i] += z.a * z.x(i);
}
// Initialize array
void init(double* x, int N)
{
for (int i=0; i < N; ++i)
x[i] = 1.0;
}
int main()
{
Timer timer;
int N = 1000000;
int iters = 20;
double Mflops = N * iters * 2 / 1000000.;
double* x = new double[N];
double* y = new double[N];
double a = .14989182;
init(x,N);
init(y,N);
timer.start();
for (int i=0; i < iters; ++i)
func1(x,y,a,N);
timer.stop();
cout << "func1: " << Mflops/timer.elapsedSeconds() << endl;
timer.start();
A z;
z.x = x;
z.y = y;
z.a = a;
z.N = N;
for (int i=0; i < iters; ++i)
func2(z);
timer.stop();
cout << "func2: " << Mflops/timer.elapsedSeconds() << endl;
timer.start();
{
C z;
z.x.data = x;
z.y.data = y;
z.a = a;
z.N = N;
for (int i=0; i < iters; ++i)
func3(z);
}
timer.stop();
cout << "func3: " << Mflops/timer.elapsedSeconds() << endl;
}
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