From 02481656966b0a8dfc95cf3c22bcc049660ff7d4 Mon Sep 17 00:00:00 2001
From: Federico Igne <git@federicoigne.com>
Date: Sat, 26 Dec 2020 17:48:38 +0000
Subject: Move Rust exercises in a subdirectory

---
 rust/grains/src/lib.rs | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 rust/grains/src/lib.rs

(limited to 'rust/grains/src/lib.rs')

diff --git a/rust/grains/src/lib.rs b/rust/grains/src/lib.rs
new file mode 100644
index 0000000..05449be
--- /dev/null
+++ b/rust/grains/src/lib.rs
@@ -0,0 +1,23 @@
+pub fn square(s: u32) -> u64 {
+    assert!(s > 0 && s < 65,"Square must be between 1 and 64");
+    2_u64.pow(s-1)
+}
+
+/// This version uses the already defined `square(s)` function.
+///
+/// There is also a faster way to compute this according to
+/// [Wolfram|Alpha](https://www.wolframalpha.com/input/?i=sum_0%5En+2%5En)
+///
+/// 2_u64.pow(65) - 1 == 18_446_744_073_709_551_615
+///
+/// this solution however doesn't work because
+///
+/// 2_u64.pow(65) == 18_446_744_073_709_551_616
+///
+/// which overflows since
+///
+/// std::u64::MAX == 18_446_744_073_709_551_615
+///
+pub fn total() -> u64 {
+    (1..65).map(square).sum() // std::u64::MAX
+}
-- 
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