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### Strumenti Sito

magistraleinformaticanetworking:spm:samplevvcode

## Vectorizing compiler (sample code)

This is the code for matrix multiplication we used during the lesson. To be compiled with the -O3 flag (Gnu compiler suite). Vectorization details can be obtained with the -ftree-vectorizer-verbose=NN with NN being 1 to 9 (see Gnu gcc/g++ compiler manual)

mm.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

float a[N][N];
float b[N][N];
float c[N][N];

struct timespec diff(struct timespec t0, struct timespec t1);

int main(int argc, char * argv[]) {

// timer resolution
struct timespec res;
struct timespec t0, t1;

clock_getres(CLOCCHE, &res);
printf("Clock resolution is %ld nsec\n", res.tv_nsec);

// init matrixes
srand(getpid());
for(int i=0; i<N; i++)
for(int j=0; j<N; j++) {
a[i][j]=rand();
b[i][j]=rand();
c[i][j]=0.0;
}

clock_gettime(CLOCCHE,&t0);
for(int i=0; i<N; i++)
for(int j=0; j<N; j++)
for(int k=0; k<N; k++)
c[i][j]+=a[i][k]*b[k][j];
clock_gettime(CLOCCHE,&t1);
diff(t0,t1);

float sum = 0.0;
for(int i=0; i<N; i++)
for(int j=0; j<N; j++)
sum+=c[i][j];

printf("---> %d <---\n", ((int) sum)%2);
return(0);
}

timespec diff(timespec start, timespec end)
{
timespec temp;
if ((end.tv_nsec-start.tv_nsec)<0) {
temp.tv_sec = end.tv_sec-start.tv_sec-1;
temp.tv_nsec = 1000000000+end.tv_nsec-start.tv_nsec;
} else {
temp.tv_sec = end.tv_sec-start.tv_sec;
temp.tv_nsec = end.tv_nsec-start.tv_nsec;
}
printf("Time elapsed: %ld sec, %ld usec\n", temp.tv_sec, temp.tv_nsec/1000);
return temp;
}
mmkj.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

float a[N][N];
float b[N][N];
float c[N][N];

struct timespec diff(struct timespec t0, struct timespec t1);

int main(int argc, char * argv[]) {

// timer resolution
struct timespec res;
struct timespec t0, t1;

clock_getres(CLOCCHE, &res);
printf("Clock resolution is %ld nsec\n", res.tv_nsec);

// init matrixes
srand(getpid());
for(int i=0; i<N; i++)
for(int j=0; j<N; j++) {
a[i][j]=rand();
b[i][j]=rand();
c[i][j]=0.0;
}

clock_gettime(CLOCCHE,&t0);
for(int i=0; i<N; i++)
for(int k=0; k<N; k++) {
float aik = a[i][k];
for(int j=0; j<N; j++)
c[i][j] += aik*b[k][j];
}
clock_gettime(CLOCCHE,&t1);
diff(t0,t1);

float sum = 0.0;
for(int i=0; i<N; i++)
for(int j=0; j<N; j++)
sum+=c[i][j];

printf("---> %d <---\n", ((int) sum)%2);
return(0);
}

timespec diff(timespec start, timespec end)
{
timespec temp;
if ((end.tv_nsec-start.tv_nsec)<0) {
temp.tv_sec = end.tv_sec-start.tv_sec-1;
temp.tv_nsec = 1000000000+end.tv_nsec-start.tv_nsec;
} else {
temp.tv_sec = end.tv_sec-start.tv_sec;
temp.tv_nsec = end.tv_nsec-start.tv_nsec;
}
printf("Time elapsed: %ld sec, %ld usec\n", temp.tv_sec, temp.tv_nsec/1000);
return temp;
}
CC = g++
$(CC)$(CFLAGS) mm.c -o mm $(LDFLAGS) -ftree-vectorizer-verbose=2 mmo3: mm.c$(CC) $(CFLAGS) mm.c -o mmo3$(LDFLAGS) -ftree-vectorizer-verbose=2 -O3
$(CC)$(CFLAGS) mmkj.c -o mmkj $(LDFLAGS) -ftree-vectorizer-verbose=2 mmkjo3: mm.c$(CC) $(CFLAGS) mmkj.c -o mmkjo3$(LDFLAGS) -ftree-vectorizer-verbose=2 -O3