Data commit

Task/Modular-exponentiation/Rust/modular-exponentiation-1.rust

@@ -0,0 +1,48 @@
+/* Add this line to the [dependencies] section of your Cargo.toml file:
+num = "0.2.0"
+*/
+
+
+use num::bigint::BigInt;
+use num::bigint::ToBigInt;
+
+
+// The modular_exponentiation() function takes three identical types
+// (which get cast to BigInt), and returns a BigInt:
+fn modular_exponentiation<T: ToBigInt>(n: &T, e: &T, m: &T) -> BigInt {
+    // Convert n, e, and m to BigInt:
+    let n = n.to_bigint().unwrap();
+    let e = e.to_bigint().unwrap();
+    let m = m.to_bigint().unwrap();
+
+    // Sanity check:  Verify that the exponent is not negative:
+    assert!(e >= Zero::zero());
+
+    use num::traits::{Zero, One};
+
+    // As most modular exponentiations do, return 1 if the exponent is 0:
+    if e == Zero::zero() {
+        return One::one()
+    }
+
+    // Now do the modular exponentiation algorithm:
+    let mut result: BigInt = One::one();
+    let mut base = n % &m;
+    let mut exp = e;
+
+    // Loop until we can return out result:
+    loop {
+        if &exp % 2 == One::one() {
+            result *= &base;
+            result %= &m;
+        }
+
+        if exp == One::one() {
+            return result
+        }
+
+        exp /= 2;
+        base *= base.clone();
+        base %= &m;
+    }
+}

Task/Modular-exponentiation/Rust/modular-exponentiation-2.rust

@@ -0,0 +1,20 @@
+fn main() {
+    let (a, b, num_digits) = (
+  "2988348162058574136915891421498819466320163312926952423791023078876139",
+  "2351399303373464486466122544523690094744975233415544072992656881240319",
+  "40",
+                    );
+
+    // Covert a, b, and num_digits to numbers:
+    let a = BigInt::parse_bytes(a.as_bytes(), 10).unwrap();
+    let b = BigInt::parse_bytes(b.as_bytes(), 10).unwrap();
+    let num_digits = num_digits.parse().unwrap();
+
+    // Calculate m from num_digits:
+    let m = num::pow::pow(10.to_bigint().unwrap(), num_digits);
+
+    // Get the result and print it:
+    let result = modular_exponentiation(&a, &b, &m);
+    println!("The last {} digits of\n{}\nto the power of\n{}\nare:\n{}",
+             num_digits, a, b, result);
+}