1 files changed, 30 insertions, 0 deletions
diff --git a/fibonacci4.c b/fibonacci4.c
new file mode 100644
index 0000000..ff250c7
--- /dev/null
+++ b/fibonacci4.c
@@ -0,0 +1,30 @@
+#include "c23-fallback.h"
+#include <stdio.h>
+
+/**
+ ** Rewrite the recursive Fibonacci such that it alternates the use of
+ ** the buffers.
+ **/
+
+void fib2rec(size_t n, size_t buf[2]) {
+  if (n) {
+    buf[n%2] += buf[!(n%2)];
+    fib2rec(n-1, buf);
+  }
+}
+
+
+size_t fib2(size_t n) {
+  size_t res[2] = { 1, 1, };
+  if (n > 2) fib2rec(n - 2, res);
+  return res[1];
+}
+
+int main(int argc, char* argv[argc+1]) {
+  for (int i = 1; i < argc; ++i) {             // process args
+    size_t const n = strtoull(argv[i], nullptr, 0); // arg -> size_t
+    printf("fib(%zu) is %zu\n",
+           n, fib2(n));
+  }
+  return EXIT_SUCCESS;
+}