1 files changed, 53 insertions, 0 deletions
diff --git a/misc/examples/algo/prime.c b/misc/examples/algo/prime.c
new file mode 100644
index 00000000..e705dcb7
--- /dev/null
+++ b/misc/examples/algo/prime.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <math.h>
+#include <time.h>
+#include <stc/cbits.h>
+#include <stc/algo/filter.h>
+#include <stc/algo/crange.h>
+
+
+cbits sieveOfEratosthenes(int64_t n)
+{
+    cbits bits = cbits_with_size(n/2 + 1, true);
+    int64_t q = (int64_t)sqrt((double) n) + 1;
+    for (int64_t i = 3; i < q; i += 2) {
+        int64_t j = i;
+        for (; j < n; j += 2) {
+            if (cbits_test(&bits, j>>1)) {
+                i = j;
+                break;
+            }
+        }
+        for (int64_t j = i*i; j < n; j += i*2)
+            cbits_reset(&bits, j>>1);
+    }
+    return bits;
+}
+
+int main(void)
+{
+    int64_t n = 1000000000;
+    printf("Computing prime numbers up to %" c_ZI "\n", n);
+
+    clock_t t1 = clock();
+    c_with (cbits primes = sieveOfEratosthenes(n + 1), cbits_drop(&primes)) {
+        int64_t np = cbits_count(&primes);
+        clock_t t2 = clock();
+
+        printf("Number of primes: %" c_ZI ", time: %f\n\n", np, (float)(t2 - t1) / (float)CLOCKS_PER_SEC);
+        puts("Show all the primes in the range [2, 1000):");
+        printf("2");
+        c_forrange (i, 3, 1000, 2)
+            if (cbits_test(&primes, i>>1)) printf(" %lld", i);
+        puts("\n");
+
+        puts("Show the last 50 primes using a temporary crange generator:");
+        crange R = crange_make(n - 1, 0, -2);
+        c_forfilter (i, crange, R
+                      , cbits_test(&primes, *i.ref>>1)
+                      , c_flt_take(i, 50)) {
+            printf("%lld ", *i.ref);
+            if (c_flt_last(i) % 10 == 0) puts("");
+        }
+    }
+}