Make N be the smallest power of 2 larger than 3*K+1

src/int_tools.c

@@ -0,0 +1,26 @@
+#include <math.h>
+#include "int_tools.h"
+
+// return smallest power of 2 that is > x
+int smallest_pow2(
+  int x
+){
+  return ipow(2,((int)log2(x)+1));
+}
+
+// integer power
+int ipow(
+  int x,
+  int n
+){
+  int out=1;
+  while (n>0)
+  {
+    if (n%2==1){
+      out*=x; 
+    }
+    n/=2;
+    x*=x;
+  }
+  return out;
+}