Added SEAL_AVOID_BRANCHING option.

microsoft · Mar 16, 2022 · 354c6ba · 354c6ba
1 parent e49178a
commit 354c6ba
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Showing 3 changed files with 13 additions and 0 deletions.
diff --git 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
@@ -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
@@ -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