Added example 6

1 files changed, 94 insertions, 0 deletions

diff --git a/06_storage/primes.c b/06_storage/primes.c
new file mode 100644
index 0000000..4a17e8d
--- /dev/null
+++ b/06_storage/primes.c
@@ -0,0 +1,94 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+#include <pthread.h>
+
+#include "primes.h"
+#include "storage.h"
+
+#define NTHREADS 16
+#define INDEX(i) ((i) >> 3)
+#define MASK(i) (unsigned char)(1 << ((i) % 8))
+
+unsigned char primes_table[TABLESIZE];
+struct interval { int low; int high; int count; };
+
+void *pthread_routine(void *);
+int primes_in_range(int, int, void (*)(const char *));
+void set_nonprime(unsigned char *, int);
+bool isprime(const unsigned char *, int);
+
+int primes_in_range(int low, int high, void (*log)(const char *)) {
+        static bool table_is_loaded = false;
+
+        pthread_t threads[NTHREADS];
+        struct interval args[NTHREADS];
+
+        if (low < 0 || high < low)
+                return 0;
+
+        if (!table_is_loaded) {
+                if (!read_table(primes_table)) {
+                        generate_primes(primes_table, log);
+                        if (!store_table(primes_table))
+                                log("Error storing table to indexed DB");
+                }
+                
+                table_is_loaded = true;
+        }
+
+        int interval_size = (high-low)/NTHREADS + 1;
+        for (int i = 0; i < NTHREADS; i++) {
+                args[i].low = low + i*interval_size;
+                args[i].high = args[i].low + interval_size;
+                pthread_create(&threads[i], NULL, pthread_routine, &args[i]);
+        }
+
+        log("All threads have started, computing..."); 
+
+        int result = 0;
+        for (int i = 0; i < NTHREADS; i++) {
+                pthread_join(threads[i], NULL);
+                result += args[i].count;
+        }
+
+        return result;
+}
+
+void set_nonprime(unsigned char *table, int n) {
+        table[INDEX(n)] &= ~MASK(n);
+}
+
+bool isprime(const unsigned char *table, int n) {
+        return table[INDEX(n)] & MASK(n);
+}
+
+void generate_primes(unsigned char *table, void (*log)(const char *)) {
+        memset(table, 0xFF, TABLESIZE);
+        set_nonprime(table, 0);
+        set_nonprime(table, 1);
+        for (long long i = 0; i < MAX_PRIME; i++) {
+                if (i % 100000000 == 0 && log != NULL) {
+                        char msg[200];
+                        sprintf(msg, 
+                            "Could not read table of primes, generating it\n"
+                            "Done %llu / %d", i, MAX_PRIME);
+                        log(msg);
+                }
+                if (!isprime(table, i))
+                        continue;
+                for (long long int j = 2*i; j < MAX_PRIME; j += i)
+                        set_nonprime(table, j);
+        }
+}
+
+void *pthread_routine(void *arg) {
+        struct interval *interval = arg;
+
+        interval->count = 0;
+        for (int i = interval->low; i < interval->high; i++)
+                if (isprime(primes_table, i))
+                        interval->count++;
+
+        return NULL;
+}