Data commit

Task/Tau-function/C/tau-function.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+
+// See https://en.wikipedia.org/wiki/Divisor_function
+unsigned int divisor_count(unsigned int n) {
+    unsigned int total = 1;
+    // Deal with powers of 2 first
+    for (; (n & 1) == 0; n >>= 1) {
+        ++total;
+    }
+    // Odd prime factors up to the square root
+    for (unsigned int p = 3; p * p <= n; p += 2) {
+        unsigned int count = 1;
+        for (; n % p == 0; n /= p) {
+            ++count;
+        }
+        total *= count;
+    }
+    // If n > 1 then it's prime
+    if (n > 1) {
+        total *= 2;
+    }
+    return total;
+}
+
+int main() {
+    const unsigned int limit = 100;
+    unsigned int n;
+
+    printf("Count of divisors for the first %d positive integers:\n", limit);
+    for (n = 1; n <= limit; ++n) {
+        printf("%3d", divisor_count(n));
+        if (n % 20 == 0) {
+            printf("\n");
+        }
+    }
+
+    return 0;
+}