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quicksort.cpp
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quicksort.cpp
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#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <limits.h>
#include <string.h>
#include <mpi.h>
#include <unistd.h>
char *int2bin(int i);
int bin2int(const char *str);
void gen_arr(int* arr, int n, int seed);
void print_array(int* arr, int len);
char* get_next_sublabel(char* label, int dim);
int pivoting(int len, int* arr, char* label, int dim);
int partition(int len, int* arr, int pivot);
int send_and_receive(int len, int** p_t_arr, int b_index, char* label, int dim);
void sequential_quicksort(int* arr, int len);
int main (int argc, char* argv[]) {
int master_id = 0;
int task_id;
int task_quant;
// just for master
double start, end, cpu_time_used;
int len = 6; // quantity of integers per process
int* arr = malloc(len * sizeof(int));;
MPI_Init(NULL, NULL);
MPI_Comm_rank(MPI_COMM_WORLD, &task_id);
MPI_Comm_size(MPI_COMM_WORLD, &task_quant);
gen_arr(arr, len, task_id);
// checking if task_quant is a power of 2.
// from https://stackoverflow.com/questions/3638431/determine-if-an-int-is-a-power-of-2-or-not-in-a-single-line
if ((task_quant & (task_quant - 1)) != 0) {
printf("number of processors was not a power of two.");
return 0;
}
int dim = (int) (log(task_quant) / log(2));
char* label = malloc(dim * sizeof(char) + 1);
label = int2bin(task_id);
label += strlen(label) - dim;
MPI_Barrier(MPI_COMM_WORLD);
if (task_id == master_id) {
printf("Master: starting the clock.\n");
start = MPI_Wtime();
}
//actual algorithm is here
for(dim = strlen(label); dim > 0; dim--){
MPI_Barrier(MPI_COMM_WORLD);
int pivot = pivoting(len, arr, label, dim);
int b_index = partition(len, arr, pivot);
MPI_Barrier(MPI_COMM_WORLD);
len = send_and_receive(len, &arr, b_index, label, dim);
}
//print_array(arr, len);
MPI_Barrier(MPI_COMM_WORLD);
if (task_id == master_id) {
printf("Master: ending the clock.\n");
end = MPI_Wtime();
cpu_time_used = end - start;
printf("We took %f time to sort the array.\n", cpu_time_used);
}
sequential_quicksort(arr, len);
// print in order
//
int token = 0;
if (task_id == master_id)
{
print_array(arr, len);
MPI_Send(&token, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
} else {
int buffer;
MPI_Status status;
MPI_Probe(MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status);
MPI_Get_count(&status, MPI_INT, &buffer);
if (buffer == 1) {
print_array(arr, len);
MPI_Recv(&token, buffer, MPI_INT, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status);
if (task_id + 1 != task_quant) {
MPI_Send(&token, 1, MPI_INT, ++task_id, 0, MPI_COMM_WORLD);
}
}
}
MPI_Finalize();
return 0;
}
void gen_arr(int* arr, int n, int seed)
{
srand((unsigned int)time(NULL) + seed);
int i;
for (i = 0; i < n; i++)
{
double scaled = (double)rand()/RAND_MAX;
arr[i] = (int) (100 - 0 +1)*scaled + 0;
}
}
void print_array(int *arr, int len) // used for debugging
{
int i;
for (i = 0; i < len; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
}
// From stackoverflow
// https://stackoverflow.com/questions/1024389/print-an-int-in-binary-representation-using-c
char * int2bin(int i)
{
size_t bits = sizeof(int) * CHAR_BIT;
char * str = malloc(bits + 1);
if(!str) return NULL;
str[bits] = 0;
// type punning because signed shift is implementation-defined
unsigned u = *(unsigned *)&i;
for(; bits--; u >>= 1)
str[bits] = u & 1 ? '1' : '0';
return str;
}
int bin2int(const char *str)
{
return (int) strtol(str, NULL, 2);
}
void sequential_quicksort(int *arr, int len)
{
if (len < 2) return;
int pivot = arr[len / 2];
int i, j;
for (i = 0, j = len - 1; ; i++, j--)
{
while (arr[i] < pivot) i++;
while (arr[j] > pivot) j--;
if (i >= j) break;
// swap pivot in
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
sequential_quicksort(arr, i);
sequential_quicksort(arr + i, len - i);
}
int pivoting(int len, int* arr, char* label, int dim)
{
MPI_Status status;
// pivot step. Either generate the pivot and send it over, or receive it.
int pivot;
// find out if I need to generate the pivot
int bool_gen_pivot = 1;
int c;
for (c = strlen(label) - dim; c < strlen(label); c++){
if (label[c] != '0'){
bool_gen_pivot = 0;
break;
}
}
if (bool_gen_pivot == 1) {
if (len == 0) { pivot = 50;}
else { pivot = arr[len - 1]; }
//send it over to the right people
char* next = malloc(strlen(label) * sizeof(char));
strcpy(next, label);
int j;
for(j = 0; j < pow(2, dim) - 1; j++) {
char* temp = get_next_sublabel(next, dim);
free(next);
next = temp;
//printf("I am %d sending %d to %d\n", bin2int(label), pivot, bin2int(next));
MPI_Send(&pivot, 1, MPI_INT, bin2int(next), 0, MPI_COMM_WORLD);
}
free(next);
} else {
char* temp = malloc(strlen(label) * sizeof(char));
strcpy(temp, label);
int j;
for (j = strlen(label) - dim; j < strlen(label); j++){
temp[j] = '0';
}
MPI_Recv(&pivot, 1, MPI_INT, bin2int(temp), 0, MPI_COMM_WORLD, &status);
//printf("I am %d receiving %d from %d\n", bin2int(label), pivot, bin2int(temp));
free(temp);
}
return pivot;
}
char* get_next_sublabel(char* label, int dim){
char* next = malloc(dim * sizeof(label));
strcpy(next, label);
char* suffix = malloc(dim * sizeof(label));
char* to_delete = suffix;
int i;
for(i = 0; i < dim; i++){
suffix[i] = label[strlen(label) - dim + i];
}
int j = bin2int(suffix);
j++;
suffix = int2bin(j);
suffix += strlen(suffix) - dim;
for(i = 0; i < dim; i++){
next[strlen(next) - dim + i] = suffix[i];
}
free(to_delete);
return next;
}
int partition(int len, int* arr, int pivot)
{
if (len == 0){ return 0; }
// claim: [0,b) is <= than pivot, [b, n) is > than pivot.
int a = 0;
int b = len;
int temp = 0;
while(a != b)
{
if (arr[a] <= pivot) {
a++;
}
else{
temp = arr[b - 1];
arr[b - 1] = arr[a];
arr[a] = temp;
b--;
}
}
if (a == 0) { return 0; }
return b;
}
int send_and_receive(int len, int** p_t_arr, int b_index, char* label, int dim){
int* arr = *p_t_arr;
MPI_Status status;
// figure out if I send the higher or the lower arr.
int receive_size;
int send_size;
int* receive;
int* send;
int* temp;
char* contact_label = malloc(sizeof(char) * strlen(label));
strcpy(contact_label, label);
if(label[strlen(label) - dim] == '0')
{
//receive lower, send higher
contact_label[strlen(label) - dim] = '1';
MPI_Probe(bin2int(contact_label), 0, MPI_COMM_WORLD, &status);
MPI_Get_count(&status, MPI_INT, &receive_size);
receive = (int *)calloc(receive_size, sizeof(int));
MPI_Recv(receive, receive_size, MPI_INT, bin2int(contact_label), 0,
MPI_COMM_WORLD, &status);
send_size = len - b_index;
send = malloc(sizeof(int) * send_size);
int i = 0;
int c;
for (c=len - 1; c > (len - send_size - 1); c--)
{
send[i] = arr[c];
i++;
}
MPI_Send(send, send_size, MPI_INT, bin2int(contact_label), 0,
MPI_COMM_WORLD);
// make new array
temp = malloc(sizeof(int) * (len - send_size + receive_size));
for(i=0; i < len - send_size; i++) { temp[i] = arr[i]; }
if (receive_size == 1 && receive[0] == -1) { receive_size = 0; }
for(i=0; i < receive_size; i++) { temp[i + len - send_size] = receive[i]; }
} else
{
//send lower, receive higher
contact_label[strlen(label) - dim] = '0';
send_size = b_index;
if(send_size == 0) // send nothing
{
send_size = 1;
send = malloc(sizeof(int));
*send = -1;
send_size = 0;
} else
{
send = malloc(sizeof(int) * send_size + 1);
int i;
for (i=0; i < send_size; i++) { send[i] = arr[i]; }
}
MPI_Send(send, send_size, MPI_INT, bin2int(contact_label), 0,
MPI_COMM_WORLD);
MPI_Probe(bin2int(contact_label), 0, MPI_COMM_WORLD, &status);
MPI_Get_count(&status, MPI_INT, &receive_size);
receive = (int *)calloc(receive_size, sizeof(int));
MPI_Recv(receive, receive_size, MPI_INT, bin2int(contact_label), 0,
MPI_COMM_WORLD, &status);
// make new array
temp = malloc(sizeof(int) * (len - send_size + receive_size));
int i;
for(i=0; i < len - send_size; i++) { temp[i] = arr[i + send_size]; }
if (receive_size == 1 && receive[0] == -1) { receive_size = 0; }
for(i=0; i < receive_size; i++) { temp[i + len - send_size] = receive[i]; }
}
free(*p_t_arr); // for some reason doesnt work
*p_t_arr = temp;
free(send);
free(receive);
free(contact_label);
return len - send_size + receive_size;
}