Add "std" feature adding requirements that don't work in std

.travis.yml

@@ -4,10 +4,20 @@ rust:
   - stable
   - beta
   - nightly
+addons:
+  apt:
+    packages:
+      - gcc-arm-none-eabi
+      - libnewlib-arm-none-eabi
 script: |
   cargo build --verbose &&
   cargo test  --verbose &&
-  cargo doc   --verbose
+  cargo doc   --verbose &&
+  cargo build --verbose --no-default-features &&
+  cargo test  --verbose --no-default-features &&
+  cargo doc   --verbose --no-default-features &&
+  rustup target add thumbv7em-none-eabihf &&
+  cargo build --verbose --no-default-features --target thumbv7em-none-eabihf
 
 matrix:
   include:

Cargo.toml

@@ -13,15 +13,20 @@ keywords = ["crypto", "curve25519", "rust-crypto"]
 categories = ["no-std", "algorithms"]
 repository = "https://github.com/shekohex/curve25519-rs"
 
-[dependencies]
-rand = "0.6.1"
+[dependencies.rand]
+version = "0.6.1"
+default-features = false
 
 [build-dependencies]
 cc = "1.0.26"
 
 [dev-dependencies]
 criterion = "0.2"
 
+[features]
+std = ["rand/std"]
+default = ["std"]
+
 [[bench]]
 name = "curve25519"
-harness = false
+harness = false

src/lib.rs

@@ -16,7 +16,12 @@ use core::{
     cmp::{min, Eq, PartialEq},
     ops::{Add, Mul, Sub},
 };
-use rand::{rngs::OsRng, Error as RndError, Rng};
+
+#[allow(unused_imports)]
+use rand::{Error as RndError, ErrorKind::Unavailable, Rng};
+
+#[cfg(feature = "std")]
+use rand::rngs::OsRng;
 
 /// Here the field is \Z/(2^255-19).
 ///
@@ -30,7 +35,7 @@ impl PartialEq for FieldElement {
     fn eq(&self, other: &FieldElement) -> bool {
         let &FieldElement(self_elems) = self;
         let &FieldElement(other_elems) = other;
-        self_elems.to_vec() == other_elems.to_vec()
+        self_elems == other_elems
     }
 }
 
@@ -2634,6 +2639,9 @@ pub fn curve25519(secret: [u8; 32], public: [u8; 32]) -> [u8; 32] {
 /// ```rust
 /// # use self::curve25519::curve25519_sk;
 /// # use rand::Error as RndError;
+/// # #[cfg(not(feature = "std"))]
+/// # fn main() { }
+/// # #[cfg(feature = "std")]
 /// # fn main() -> Result<(), RndError> {
 /// // Let curve25519_sk generate the random 32-byte value.
 /// let sk1 = curve25519_sk(None)?;
@@ -2646,17 +2654,26 @@ pub fn curve25519(secret: [u8; 32], public: [u8; 32]) -> [u8; 32] {
 /// # }
 /// ```
 pub fn curve25519_sk(rand: Option<[u8; 32]>) -> Result<[u8; 32], RndError> {
-    let mut buf: [u8; 32] = [0; 32];
-
     // Fill a 32-byte buffer with random values if necessary.
     // Otherwise, use the given 32-byte value.
     let mut rand: [u8; 32] = match rand {
         Some(r) => r,
+
+        #[cfg(feature = "std")]
         None => {
             let mut rng = OsRng::new()?;
+            let mut buf: [u8; 32] = [0; 32];
             rng.fill(&mut buf);
             buf
         },
+
+        #[cfg(not(feature = "std"))]
+        None => {
+            return Err(RndError::new(
+                Unavailable,
+                "Cannot generate random without Standard Library",
+            ));
+        },
     };
 
     // curve25519 secret key bit manip.