Data commit

Task/Blum-integer/C/blum-integer.c

@@ -0,0 +1,71 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <locale.h>
+
+int inc[8] = {4, 2, 4, 2, 4, 6, 2, 6};
+
+bool isPrime(int n) {
+    if (n < 2) return false;
+    if (n%2 == 0) return n == 2;
+    if (n%3 == 0) return n == 3;
+    int d = 5;
+    while (d*d <= n) {
+        if (n%d == 0) return false;
+        d += 2;
+        if (n%d == 0) return false;
+        d += 4;
+    }
+    return true;
+}
+
+// Assumes n is odd.
+int firstPrimeFactor(int n) {
+    if (n == 1) return 1;
+    if (!(n%3)) return 3;
+    if (!(n%5)) return 5;
+    for (int k = 7, i = 0; k*k <= n; ) {
+        if (!(n%k)) {
+            return k;
+        } else {
+            k += inc[i];
+            i = (i + 1) % 8;
+        }
+    }
+    return n;
+}
+
+int main() {
+    int i = 1, j, bc = 0, p, q;
+    int blum[50], counts[4] = {0}, digits[4] = {1, 3, 5, 7};
+    setlocale(LC_NUMERIC, "");
+    while (true) {
+        p = firstPrimeFactor(i);
+        if (p % 4 == 3) {
+            q = i / p;
+            if (q != p && q % 4 == 3 && isPrime(q)) {
+                if (bc < 50) blum[bc] = i;
+                ++counts[i % 10 / 3];
+                ++bc;
+                if (bc == 50) {
+                    printf("First 50 Blum integers:\n");
+                    for (j = 0; j < 50; ++j) {
+                        printf("%3d ", blum[j]);
+                        if (!((j+1) % 10)) printf("\n");
+                    }
+                    printf("\n");
+                } else if (bc == 26828 || !(bc % 100000)) {
+                    printf("The %'7dth Blum integer is: %'9d\n", bc, i);
+                    if (bc == 400000) {
+                        printf("\n%% distribution of the first 400,000 Blum integers:\n");
+                        for (j = 0; j < 4; ++j) {
+                            printf("  %6.3f%% end in %d\n", counts[j]/4000.0, digits[j]);
+                        }
+                        break;
+                    }
+                }
+            }
+        }
+        i += (i % 5 == 3) ? 4 : 2;
+    }
+    return 0;
+}