init

.gitignore

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+/target

.vscode/launch.json

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+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "type": "lldb",
+            "request": "launch",
+            "name": "Debug executable 'isprime'",
+            "cargo": {
+                "args": [
+                    "build",
+                    "--bin=isprime",
+                    "--package=isprime"
+                ],
+                "filter": {
+                    "name": "isprime",
+                    "kind": "bin"
+                }
+            },
+            "args": [],
+            "cwd": "${workspaceFolder}"
+        },
+        {
+            "type": "lldb",
+            "request": "launch",
+            "name": "Debug unit tests in executable 'isprime'",
+            "cargo": {
+                "args": [
+                    "test",
+                    "--no-run",
+                    "--bin=isprime",
+                    "--package=isprime"
+                ],
+                "filter": {
+                    "name": "isprime",
+                    "kind": "bin"
+                }
+            },
+            "args": [],
+            "cwd": "${workspaceFolder}"
+        }
+    ]
+}

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "autocfg"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
+
+[[package]]
+name = "isprime"
+version = "0.1.0"
+dependencies = [
+ "num-bigint",
+]
+
+[[package]]
+name = "num-bigint"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f93ab6289c7b344a8a9f60f88d80aa20032336fe78da341afc91c8a2341fc75f"
+dependencies = [
+ "autocfg",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-integer"
+version = "0.1.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "225d3389fb3509a24c93f5c29eb6bde2586b98d9f016636dff58d7c6f7569cd9"
+dependencies = [
+ "autocfg",
+ "num-traits",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "578ede34cf02f8924ab9447f50c28075b4d3e5b269972345e7e0372b38c6cdcd"
+dependencies = [
+ "autocfg",
+]

Cargo.toml

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+[package]
+name = "isprime"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+num-bigint = "0.4.3"

src/main.rs

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+use std::io::{self, Write};
+use num_bigint::BigUint;
+
+fn log_2(x: BigUint) -> u64 {
+    x.bits() - 1
+}
+
+fn is_prime(number: BigUint) -> bool {
+    let a = log_2(number.clone()+1u8);
+    if BigUint::from(2u8).pow(a as u32)-BigUint::from(1u8) != number {
+        eprintln!("only supports numbers of type (2^x)-1");
+        std::process::exit(1);
+    }
+
+    let mut last = BigUint::from(4u8)%number.clone();
+    let two = BigUint::from(2u8);
+    for _i in 2..a {
+        last = (last.clone()*last-two.clone())%number.clone();
+    }
+    if last == BigUint::from(0u8) {
+        true
+    } else {
+        false
+    }
+}
+
+fn main() {
+    let mut buffer = String::new();
+    let stdin = io::stdin();
+    print!("please enter the number to check: ");
+    io::stdout().flush().expect("could not flush");
+    stdin.read_line(&mut buffer).expect("could not read from stdin");
+    buffer = buffer.trim().to_owned();
+    
+    let number = BigUint::parse_bytes(&buffer.as_bytes(), 10).expect("expected number");
+
+    // number = 2^x - 1
+    // x = log2(number + 1)
+
+    if is_prime(number.clone()) {
+        println!("{number} is a prime");
+    } else {
+        println!("{number} is not a prime");
+    }
+}