From 98bab6877a2f06b9b6eae1d56ece59a93767caab Mon Sep 17 00:00:00 2001
From: str4d <str4d@mail.i2p>
Date: Thu, 17 May 2018 09:34:16 +1200
Subject: [PATCH] Add read_le and write_le to PrimeFieldRepr

---
 src/lib.rs        | 22 ++++++++++++++++++++++
 src/tests/repr.rs | 43 ++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 481ff26..930d806 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -407,6 +407,28 @@ pub trait PrimeFieldRepr:
 
         Ok(())
     }
+
+    /// Writes this `PrimeFieldRepr` as a little endian integer.
+    fn write_le<W: Write>(&self, mut writer: W) -> io::Result<()> {
+        use byteorder::{LittleEndian, WriteBytesExt};
+
+        for digit in self.as_ref().iter() {
+            writer.write_u64::<LittleEndian>(*digit)?;
+        }
+
+        Ok(())
+    }
+
+    /// Reads a little endian integer into this representation.
+    fn read_le<R: Read>(&mut self, mut reader: R) -> io::Result<()> {
+        use byteorder::{LittleEndian, ReadBytesExt};
+
+        for digit in self.as_mut().iter_mut() {
+            *digit = reader.read_u64::<LittleEndian>()?;
+        }
+
+        Ok(())
+    }
 }
 
 #[derive(Debug, PartialEq)]
diff --git a/src/tests/repr.rs b/src/tests/repr.rs
index 3b9d76d..681a476 100644
--- a/src/tests/repr.rs
+++ b/src/tests/repr.rs
@@ -12,13 +12,46 @@ fn random_encoding_tests<R: PrimeFieldRepr>() {
 
     for _ in 0..1000 {
         let r = R::rand(&mut rng);
-        let mut rdecoded = R::default();
 
-        let mut v: Vec<u8> = vec![];
-        r.write_be(&mut v).unwrap();
-        rdecoded.read_be(&v[0..]).unwrap();
+        // Big endian
+        {
+            let mut rdecoded = R::default();
 
-        assert_eq!(r, rdecoded);
+            let mut v: Vec<u8> = vec![];
+            r.write_be(&mut v).unwrap();
+            rdecoded.read_be(&v[0..]).unwrap();
+
+            assert_eq!(r, rdecoded);
+        }
+
+        // Little endian
+        {
+            let mut rdecoded = R::default();
+
+            let mut v: Vec<u8> = vec![];
+            r.write_le(&mut v).unwrap();
+            rdecoded.read_le(&v[0..]).unwrap();
+
+            assert_eq!(r, rdecoded);
+        }
+
+        {
+            let mut rdecoded_le = R::default();
+            let mut rdecoded_be_flip = R::default();
+
+            let mut v: Vec<u8> = vec![];
+            r.write_le(&mut v).unwrap();
+
+            // This reads in little-endian, so we are done.
+            rdecoded_le.read_le(&v[..]).unwrap();
+
+            // This reads in big-endian, so we perform a swap of the
+            // bytes beforehand.
+            let v: Vec<u8> = v.into_iter().rev().collect();
+            rdecoded_be_flip.read_be(&v[..]).unwrap();
+
+            assert_eq!(rdecoded_le, rdecoded_be_flip);
+        }
     }
 }