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diff --git a/rand/rand_pcg/src/pcg128.rs b/rand/rand_pcg/src/pcg128.rs
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+// Copyright 2018 Developers of the Rand project.
+// Copyright 2017 Paul Dicker.
+// Copyright 2014-2017 Melissa O'Neill and PCG Project contributors
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! PCG random number generators
+
+// This is the default multiplier used by PCG for 64-bit state.
+const MULTIPLIER: u128 = 0x2360_ED05_1FC6_5DA4_4385_DF64_9FCC_F645;
+
+use core::fmt;
+use core::mem::transmute;
+use rand_core::{RngCore, SeedableRng, Error, le};
+
+/// A PCG random number generator (XSL 128/64 (MCG) variant).
+///
+/// Permuted Congruential Generator with 128-bit state, internal Multiplicative
+/// Congruential Generator, and 64-bit output via "xorshift low (bits),
+/// random rotation" output function.
+///
+/// This is a 128-bit MCG with the PCG-XSL-RR output function.
+/// Note that compared to the standard `pcg64` (128-bit LCG with PCG-XSL-RR
+/// output function), this RNG is faster, also has a long cycle, and still has
+/// good performance on statistical tests.
+///
+/// Note: this RNG is only available using Rust 1.26 or later.
+#[derive(Clone)]
+#[cfg_attr(feature="serde1", derive(Serialize,Deserialize))]
+pub struct Mcg128Xsl64 {
+    state: u128,
+}
+
+/// A friendly name for `Mcg128Xsl64`.
+pub type Pcg64Mcg = Mcg128Xsl64;
+
+impl Mcg128Xsl64 {
+    /// Construct an instance compatible with PCG seed.
+    ///
+    /// Note that PCG specifies a default value for the parameter:
+    ///
+    /// - `state = 0xcafef00dd15ea5e5`
+    pub fn new(state: u128) -> Self {
+        // Force low bit to 1, as in C version (C++ uses `state | 3` instead).
+        Mcg128Xsl64 { state: state | 1 }
+    }
+}
+
+// Custom Debug implementation that does not expose the internal state
+impl fmt::Debug for Mcg128Xsl64 {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Mcg128Xsl64 {{}}")
+    }
+}
+
+/// We use a single 126-bit seed to initialise the state and select a stream.
+/// Two `seed` bits (lowest order of last byte) are ignored.
+impl SeedableRng for Mcg128Xsl64 {
+    type Seed = [u8; 16];
+
+    fn from_seed(seed: Self::Seed) -> Self {
+        // Read as if a little-endian u128 value:
+        let mut seed_u64 = [0u64; 2];
+        le::read_u64_into(&seed, &mut seed_u64);
+        let state = (seed_u64[0] as u128) |
+                    (seed_u64[1] as u128) << 64;
+        Mcg128Xsl64::new(state)
+    }
+}
+
+impl RngCore for Mcg128Xsl64 {
+    #[inline]
+    fn next_u32(&mut self) -> u32 {
+        self.next_u64() as u32
+    }
+
+    #[inline]
+    fn next_u64(&mut self) -> u64 {
+        // prepare the LCG for the next round
+        let state = self.state.wrapping_mul(MULTIPLIER);
+        self.state = state;
+
+        // Output function XSL RR ("xorshift low (bits), random rotation")
+        // Constants are for 128-bit state, 64-bit output
+        const XSHIFT: u32 = 64;     // (128 - 64 + 64) / 2
+        const ROTATE: u32 = 122;    // 128 - 6
+
+        let rot = (state >> ROTATE) as u32;
+        let xsl = ((state >> XSHIFT) as u64) ^ (state as u64);
+        xsl.rotate_right(rot)
+    }
+
+    #[inline]
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        // specialisation of impls::fill_bytes_via_next; approx 3x faster
+        let mut left = dest;
+        while left.len() >= 8 {
+            let (l, r) = {left}.split_at_mut(8);
+            left = r;
+            let chunk: [u8; 8] = unsafe {
+                transmute(self.next_u64().to_le())
+            };
+            l.copy_from_slice(&chunk);
+        }
+        let n = left.len();
+        if n > 0 {
+            let chunk: [u8; 8] = unsafe {
+                transmute(self.next_u64().to_le())
+            };
+            left.copy_from_slice(&chunk[..n]);
+        }
+    }
+
+    #[inline]
+    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
+        Ok(self.fill_bytes(dest))
+    }
+}