From 4590d98e042ab7f61ae2ecc6c40cce06a2d11333 Mon Sep 17 00:00:00 2001
From: Jeffrey Walton <noloader@gmail.com>
Date: Tue, 30 Apr 2019 17:16:41 -0400
Subject: [PATCH] Disable move_conditional_bytes until it can be tested

---
 donna_32.cpp | 8 ++++++--
 donna_64.cpp | 8 ++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/donna_32.cpp b/donna_32.cpp
index 28ae82df..2e07834a 100644
--- a/donna_32.cpp
+++ b/donna_32.cpp
@@ -927,8 +927,12 @@ curve25519_contract(byte out[32], const bignum25519 in) {
 
 /* out = (flag) ? in : out */
 inline void
-curve25519_move_conditional_bytes(byte out[96], const byte in[96], word32 flag) {
-#if defined(__GNUC__) && defined(__i686__)
+curve25519_move_conditional_bytes(byte out[96], const byte in[96], word32 flag)
+{
+    // TODO: enable this code path once we can test and benchmark it.
+    // It is about 48 insns shorter, it avoids punning which may be UB,
+    // and it is guaranteed constant time.
+#if defined(__GNUC__) && defined(__i686__) && 0
     const word32 iter = 96/sizeof(word32);
     word32* outl = reinterpret_cast<word32*>(out);
     const word32* inl = reinterpret_cast<const word32*>(in);
diff --git a/donna_64.cpp b/donna_64.cpp
index a1d22c4e..1a67ed38 100644
--- a/donna_64.cpp
+++ b/donna_64.cpp
@@ -749,8 +749,12 @@ curve25519_contract(byte *out, const bignum25519 input) {
 
 /* out = (flag) ? in : out */
 inline void
-curve25519_move_conditional_bytes(byte out[96], const byte in[96], word64 flag) {
-#if defined(__GNUC__) && defined(__x86_64__)
+curve25519_move_conditional_bytes(byte out[96], const byte in[96], word64 flag)
+{
+    // TODO: enable this code path once we can test and benchmark it.
+    // It is about 24 insns shorter, it avoids punning which may be UB,
+    // and it is guaranteed constant time.
+#if defined(__GNUC__) && defined(__x86_64__) && 0
     const word32 iter = 96/sizeof(word64);
     word64* outq = reinterpret_cast<word64*>(out);
     const word64* inq = reinterpret_cast<const word64*>(in);