1 files changed, 30 insertions, 0 deletions
diff --git a/fibonacci5.c b/fibonacci5.c
new file mode 100644
index 0000000..c642aa5
--- /dev/null
+++ b/fibonacci5.c
@@ -0,0 +1,30 @@
+#include "c23-fallback.h"
+#include <stdio.h>
+
+/**
+ ** Rewrite the recursive Fibonacci such that it unrolls two
+ ** successive recursive calls.
+ **/
+
+void fib2rec(size_t n, size_t buf[2]) {
+  if (n > 1) {
+    buf[0] += buf[1];
+    buf[1] += buf[0];
+    fib2rec(n-2, buf);
+  }
+}
+
+size_t fib2(size_t n) {
+  size_t res[2] = { 1, 1, };
+  if (n > 2) fib2rec(n-1, res);
+  return res[!(n%2)];
+}
+
+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;
+}