[tor-commits] [tor/master] Enable ed25519-donna's SSE2 code when possible for 32 bit x86.

[nickm at torproject.org]

commit a77616f6056a9dbb5722600ff2465d8ec5b3d063
Author: Yawning Angel <yawning at schwanenlied.me>
Date:   Mon Aug 17 18:41:41 2015 +0000

    Enable ed25519-donna's SSE2 code when possible for 32 bit x86.
    
    This probably requires the user to manually set CFLAGS, but should
    result in a net gain on 32 bit x86. Enabling SSE2 support would be
    possible on x86_64, but will result in slower performance.
    
    Implements feature #16535.
---
 changes/feature16535                           |    4 ++++
 src/ext/ed25519/donna/README.tor               |    4 ++++
 src/ext/ed25519/donna/ed25519-donna-portable.h |   10 ++++++++++
 3 files changed, 18 insertions(+)

diff --git a/changes/feature16535 b/changes/feature16535
new file mode 100644
index 0000000..3df46b6
--- /dev/null
+++ b/changes/feature16535
@@ -0,0 +1,4 @@
+  o Minor features (performance)
+    - Improve the runtime speed of Ed25519 operations and Curve25519 keypair
+      generation when built targeting 32 bit x86 platforms with SSE2
+      available. Implements ticket 16535.
diff --git a/src/ext/ed25519/donna/README.tor b/src/ext/ed25519/donna/README.tor
index 2bb0efc..026d180 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 9ec83b8..1cd644c 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>