feat: add pi

__std/pi/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "pi"
+version = "0.1.0"

__std/pi/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "pi"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

__std/pi/src/main.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let mut pi = 1f64;
+    for i in 1..1000000000u64 {
+        pi += if i % 2 == 1 { -1f64 } else { 1f64 } / (1f64 + i as f64 * 2f64);
+    }
+    println!("pi = {}", pi * 4f64);
+}