From b3e9e62599532050fc776c5e8f076915b56c2235 Mon Sep 17 00:00:00 2001
From: David Faulkner <d@davo.co>
Date: Fri, 7 Aug 2026 23:40:47 -0500
Subject: Import official C23 code examples for Modern C (Jens Gustedt, 2024)

- Add official C source files, Makefile, c23-fallback.h, and LICENSE
- Update README.md with study mirror notice
---
 fibonacciRet.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 fibonacciRet.c

(limited to 'fibonacciRet.c')

diff --git a/fibonacciRet.c b/fibonacciRet.c
new file mode 100644
index 0000000..bfefa80
--- /dev/null
+++ b/fibonacciRet.c
@@ -0,0 +1,46 @@
+#include "c23-fallback.h"
+#include <stdio.h>
+
+typedef struct fibonaccipair fibonaccipair;
+
+struct fibonaccipair {
+  size_t prev;
+  size_t act;
+};
+
+fibonaccipair fiboNext(fibonaccipair ret) {
+  size_t res = ret.act + ret.prev;
+  ret.prev = ret.act;
+  ret.act = res;
+  return ret;
+}
+
+fibonaccipair fibonacci2(size_t n, fibonaccipair ret) {
+  if (n) {
+    return fibonacci2(n-1, fiboNext(ret));
+  } else
+    return ret;
+}
+
+fibonaccipair fibonacci3(size_t n, fibonaccipair ret) {
+  while (n --> 0) {
+    ret = fiboNext(ret);
+  }
+  return ret;
+}
+
+size_t fibonacci(size_t n) {
+  register fibonaccipair res = { 1, 1, };
+  if (n > 2) res = fibonacci2(n - 2, res);
+  return res.act;
+}
+
+
+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("fibonacci(%zu) is %zu\n",
+           n, fibonacci(n));
+  }
+  return EXIT_SUCCESS;
+}
-- 
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