Refactor interface to be compatible with rust-crypto

Cargo.toml

@@ -3,7 +3,7 @@ name = "rust-scrypt"
 authors = ["Constantine Kryvomaz <[email protected]>"]
 description = "Bindings into C for Tarsnap's `Scrypt` algorithm"
 repository = "https://github.com/r8d8/rust-scrypt"
-version = "1.2.0"
+version = "1.3.0"
 build = "build.rs"
 keywords = ["rust", "crypto", "scrypt"]
 readme = "README.md"

src/lib.rs

@@ -5,6 +5,8 @@
 #![cfg_attr(feature = "dev", plugin(clippy))]
 #![allow(non_upper_case_globals)]
 
+use std::mem::size_of;
+
 #[link(name = "scrypt")]
 extern "C" {
     pub fn crypto_scrypt(
@@ -33,6 +35,26 @@ pub struct ScryptParams {
     pub p: u32,
 }
 
+impl ScryptParams {
+
+    ///Create a new instance of ScryptParams
+    /// 
+    /// # Arguments:
+    /// log_n - The log2 of the Scrypt parameter N
+    /// r - The Scrypt parameter r
+    /// p - The Scrypt parameter p
+    /// 
+    pub fn new(n: u64, r: u32, p: u32) -> ScryptParams {
+        assert!(r > 0);
+        assert!(p > 0);
+        assert!(n > 0);
+        assert!(size_of::<usize>() >= size_of::<u32>() || (r <= std::usize::MAX as u32 && p < std::usize::MAX as u32));
+
+        ScryptParams { n,r, p }
+    }
+
+}
+
 /// Derive fixed size key for given `salt` and `passphrase`
 ///
 /// #Arguments: