C: sum of multiples + complex numbers

c/sum-of-multiples/src/sum_of_multiples.c

@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <malloc.h>
+
+/* V1: initial version
+ * V2: bug fix: force full unsigned allocation instead of bytes.
+ */
+#include "sum_of_multiples.h"
+
+#define BITS (sizeof(unsigned)*8)
+
+#define getbit(i) (!!(sieve[(i) / BITS] & (1 << ((i) % BITS))))
+#define setbit(i) (sieve[(i) / BITS] |= (1 << ((i) % BITS)))
+
+/* use a kind of eratosthenes's sieve, to avoid the trivial solution :-)
+ */
+unsigned sum(const unsigned *f, const size_t n, const unsigned l)
+{
+    unsigned sieve_size = (l-1)/BITS+1;
+    unsigned num, i, res=0;
+    unsigned *sieve;
+
+    sieve = calloc(sieve_size, sizeof(unsigned)); /* l bits array */
+    if (!sieve)
+        return 0;
+    for (i=0; i<n; ++i) {
+        if (f[i]) {
+            for (num=f[i]; num<l; num+=f[i]) {
+                if (!getbit(num)) {
+                    res+=num;
+                    setbit(num);
+                }
+            }
+
+        }
+    }
+    free(sieve);
+    return res;
+}
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#ifdef UNIT_TEST
+int main(int ac, char **av)
+{
+    unsigned input[256];
+    int last, i;
+    if (ac>2) {
+        last=atol(av[1]);
+        for (i=2; i<ac; ++i) {
+            input[i-2]=atoi(av[i]);
+        }
+        printf("sum(..., %u, %u)=%u\n", i-2, last,
+               sum(input, (unsigned)i-2, (unsigned)last));
+    }
+}
+#endif