Rename Random impl to Rng.

Create Random struct providing next_x(range) for all T:Rng.

embassy-traits/src/rng.rs

@@ -17,11 +17,60 @@ pub trait Rng {
     fn fill_bytes<'a>(&'a mut self, dest: &'a mut [u8]) -> Self::RngFuture<'a>;
 }
 
-pub trait Random: Rng {
-    #[rustfmt::skip]
-    type NextFuture<'a>: Future<Output = Result<u32, <Self as Rng>::Error>> + 'a
-    where
-        Self: 'a;
-
-    fn next<'a>(&'a mut self, range: u32) -> Self::NextFuture<'a>;
+pub struct Random<T: Rng> {
+    rng: T,
+}
+
+impl<T: Rng> Random<T> {
+    pub fn new(rng: T) -> Self {
+        Self { rng }
+    }
+
+    pub async fn next_u8<'a>(&'a mut self, range: u8) -> Result<u8, T::Error> {
+        // Lemire's method
+        let t = (-(range as i8) % (range as i8)) as u8;
+        loop {
+            let mut buf = [0; 1];
+            self.rng.fill_bytes(&mut buf).await?;
+            let x = u8::from_le_bytes(buf);
+            let m = x as u16 * range as u16;
+            let l = m as u8;
+            if l < t {
+                continue;
+            }
+            return Ok((m >> 8) as u8);
+        }
+    }
+
+    pub async fn next_u16<'a>(&'a mut self, range: u16) -> Result<u16, T::Error> {
+        // Lemire's method
+        let t = (-(range as i16) % (range as i16)) as u16;
+        loop {
+            let mut buf = [0; 2];
+            self.rng.fill_bytes(&mut buf).await?;
+            let x = u16::from_le_bytes(buf);
+            let m = x as u32 * range as u32;
+            let l = m as u16;
+            if l < t {
+                continue;
+            }
+            return Ok((m >> 16) as u16);
+        }
+    }
+
+    pub async fn next_u32<'a>(&'a mut self, range: u32) -> Result<u32, T::Error> {
+        // Lemire's method
+        let t = (-(range as i32) % (range as i32)) as u32;
+        loop {
+            let mut buf = [0; 4];
+            self.rng.fill_bytes(&mut buf).await?;
+            let x = u32::from_le_bytes(buf);
+            let m = x as u64 * range as u64;
+            let l = m as u32;
+            if l < t {
+                continue;
+            }
+            return Ok((m >> 32) as u32);
+        }
+    }
 }