From 649c1759e8b56f0ac31dd31e46eae81b7ffd1e2c Mon Sep 17 00:00:00 2001
From: Huon Wilson <dbau.pp+github@gmail.com>
Date: Wed, 9 Oct 2013 02:13:34 +1100
Subject: [PATCH] std::rand::reader: describe cfg!(endianness).

---
 src/libstd/rand/reader.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/libstd/rand/reader.rs b/src/libstd/rand/reader.rs
index 78dad30117da..961a5b2cd286 100644
--- a/src/libstd/rand/reader.rs
+++ b/src/libstd/rand/reader.rs
@@ -47,6 +47,9 @@ impl<R: Reader> ReaderRng<R> {
 
 impl<R: Reader> Rng for ReaderRng<R> {
     fn next_u32(&mut self) -> u32 {
+        // This is designed for speed: reading a LE integer on a LE
+        // platform just involves blitting the bytes into the memory
+        // of the u32, similarly for BE on BE; avoiding byteswapping.
         if cfg!(target_endian="little") {
             self.reader.read_le_u32_()
         } else {
@@ -54,6 +57,7 @@ impl<R: Reader> Rng for ReaderRng<R> {
         }
     }
     fn next_u64(&mut self) -> u64 {
+        // see above for explanation.
         if cfg!(target_endian="little") {
             self.reader.read_le_u64_()
         } else {