restructurization

_snippets/simple_Eratosfen_sieve.c

@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <stdlib.h>
+#include <omp.h>
+#include <usefull_macros.h>
+
+// 1GB of RAM
+#define MASKSZ      (1073741824L)
+#define MNUMBERS    (MASKSZ*8)
+static uint8_t *masks;
+
+static inline __attribute__((always_inline)) uint8_t get(uint64_t idx){
+    register uint64_t i = idx >> 3;
+    register uint8_t j = idx - (i<<3);
+    return masks[i] & (1<<j);
+}
+
+static inline __attribute__((always_inline)) void reset(uint64_t idx){
+    register uint64_t i = idx >> 3;
+    register uint8_t j = idx - (i<<3);
+    masks[i] &= ~(1<<j);
+}
+
+int main(){
+    masks = malloc(MASKSZ);
+    double t0 = dtime();
+    memset(masks, 0b10101010, MASKSZ); // without even numbers
+    masks[0] = 0b10101100; // with 2 and withoun 0 and 1
+    for(uint64_t i = 3; i < 64; i += 2){
+        if(get(i)){
+            for(uint64_t j = i*2; j < MNUMBERS; j += i){
+                reset(j);
+            }
+        }
+    }
+    printf("\tfirst 64: %g\n", dtime()-t0);
+#define THREADNO	8
+    omp_set_num_threads(THREADNO);
+#pragma omp parallel for shared(masks)
+    for(uint64_t i = 0; i < THREADNO; ++i){
+        for(uint64_t idx = 65 + 2*omp_get_thread_num(); idx < MNUMBERS; idx += THREADNO*2){
+        if(get(idx)){
+            for(uint64_t j = idx*2; j < MNUMBERS; j += idx){
+                reset(j);
+            }
+        }}
+    }
+    printf("\tfull table: %g\n", dtime()-t0);
+    for(uint64_t i = 0; i < 1000; ++i){
+        if(get(i)) printf("%zd\n", i);
+    }
+	for(uint64_t last = MNUMBERS-1; last > 1000; --last){
+		if(get(last)){ printf("last in list: %zd\n", last); break;}
+	}
+    return 0;
+}