From 354c6ba9454834c33efdfcc3c00bc3f37d729bd4 Mon Sep 17 00:00:00 2001
From: Wei Dai <wei.dai@microsoft.com>
Date: Tue, 15 Mar 2022 23:33:42 -0700
Subject: [PATCH] Added SEAL_AVOID_BRANCHING option.

---
 CMakeLists.txt                   | 7 +++++++
 native/src/seal/util/config.h.in | 1 +
 native/src/seal/util/defines.h   | 5 +++++
 3 files changed, 13 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5d85e8e6e..22122d8b5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -265,6 +265,13 @@ set_property(CACHE SEAL_DEFAULT_PRNG PROPERTY
     STRINGS "Blake2xb" "Shake256")
 mark_as_advanced(FORCE SEAL_DEFAULT_PRNG)
 
+# [option] SEAL_AVOID_BRANCHING (default: OFF)
+# Avoid branching in conditional move operations if set to ON, use faster method if set to OFF.
+set(SEAL_AVOID_BRANCHING_STR "Use an always branching-free conditional move")
+option(SEAL_AVOID_BRANCHING ${SEAL_AVOID_BRANCHING_STR} OFF)
+message(STATUS "SEAL_AVOID_BRANCHING: ${SEAL_AVOID_BRANCHING}")
+mark_as_advanced(FORCE SEAL_AVOID_BRANCHING)
+
 # [option] SEAL_USE_INTRIN (default: ON)
 set(SEAL_USE_INTRIN_OPTION_STR "Use intrinsics")
 option(SEAL_USE_INTRIN ${SEAL_USE_INTRIN_OPTION_STR} ON)
diff --git a/native/src/seal/util/config.h.in b/native/src/seal/util/config.h.in
index a28adc2af..1b0993a5f 100644
--- a/native/src/seal/util/config.h.in
+++ b/native/src/seal/util/config.h.in
@@ -24,6 +24,7 @@
 #cmakedefine SEAL_THROW_ON_TRANSPARENT_CIPHERTEXT
 #cmakedefine SEAL_USE_GAUSSIAN_NOISE
 #cmakedefine SEAL_DEFAULT_PRNG @SEAL_DEFAULT_PRNG@
+#cmakedefine SEAL_AVOID_BRANCHING
 
 // Intrinsics
 #cmakedefine SEAL_USE_INTRIN
diff --git a/native/src/seal/util/defines.h b/native/src/seal/util/defines.h
index 8de72bd6c..1f3770536 100644
--- a/native/src/seal/util/defines.h
+++ b/native/src/seal/util/defines.h
@@ -285,4 +285,9 @@ namespace seal
 
 // Conditionally select the former if true and the latter if false
 // This is a temporary solution that generates constant-time code with all compilers on all platforms.
+#ifndef SEAL_AVOID_BRANCHING
 #define SEAL_COND_SELECT(cond, if_true, if_false) (cond ? if_true : if_false)
+#else
+#define SEAL_COND_SELECT(cond, if_true, if_false) \
+    ((if_false) ^ ((~static_cast<uint64_t>(cond) + 1) & ((if_true) ^ (if_false))))
+#endif