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-rw-r--r--src/ext/ed25519/donna/README.tor4
-rw-r--r--src/ext/ed25519/donna/ed25519-donna-portable.h10
2 files changed, 14 insertions, 0 deletions
diff --git a/src/ext/ed25519/donna/README.tor b/src/ext/ed25519/donna/README.tor
index 2bb0efc012..026d180c24 100644
--- a/src/ext/ed25519/donna/README.tor
+++ b/src/ext/ed25519/donna/README.tor
@@ -40,3 +40,7 @@ as of 8757bd4cd209cb032853ece0ce413f122eef212c.
* On non-x86 targets, GCC's Stack Protector dislikes variables that have
alignment constraints greater than that of other primitive types.
The `ALIGN` macro is thus no-oped for all non-SSE2 builds.
+
+ * On 32 bit x86 targets that the compiler thinks supports SSE2, always
+ enable SSE2 support by force defining ED25519_SSE2 (x86_64 would also
+ always support this, but that code path is slower).
diff --git a/src/ext/ed25519/donna/ed25519-donna-portable.h b/src/ext/ed25519/donna/ed25519-donna-portable.h
index 9ec83b87e3..1cd644c003 100644
--- a/src/ext/ed25519/donna/ed25519-donna-portable.h
+++ b/src/ext/ed25519/donna/ed25519-donna-portable.h
@@ -158,6 +158,16 @@ static inline void U64TO8_LE(unsigned char *p, const uint64_t v) {
#define ALIGN(x)
#endif
+/* Tor: Force enable SSE2 on 32 bit x86 systems if the compile target
+ * architecture supports it. This is not done on x86-64 as the non-SSE2
+ * code benchmarks better, at least on Haswell.
+ */
+#if defined(__SSE2__) && !defined(CPU_X86_64)
+ /* undef in case it's manually specified... */
+ #undef ED25519_SSE2
+ #define ED25519_SSE2
+#endif
+
#include <stdlib.h>
#include <string.h>