prefer_openssl: autodetect whether to use OpenSSL or Go GCM

Go GCM is faster than OpenSSL if the CPU has AES instructions
and you are running Go 1.6+.

The "-openssl" option now defaults to "auto".

"gocryptfs -debug -version" displays the result of the autodetection.

See https://github.com/rfjakob/gocryptfs/issues/23 for details and
benchmarks.

1 files changed, 23 insertions, 0 deletions

diff --git a/internal/prefer_openssl/prefer_test.go b/internal/prefer_openssl/prefer_test.go
new file mode 100644
index 0000000..a2ed737
--- /dev/null
+++ b/internal/prefer_openssl/prefer_test.go
@@ -0,0 +1,23 @@
+package prefer_openssl
+
+import (
+	"testing"
+)
+
+func TestCurrentCPU(t *testing.T) {
+	t.Logf("PreferOpenSSL=%v", PreferOpenSSL())
+}
+
+// Has AES instructions
+func TestXeonE312xx(t *testing.T) {
+	if filePreferOpenSSL("cpuinfo.xeon_e312xx.txt") == true {
+		t.Fail()
+	}
+}
+
+// Pentium G do not have AES instructions
+func TestPentiumG630(t *testing.T) {
+	if filePreferOpenSSL("cpuinfo.pentium_g630.txt") == false {
+		t.Fail()
+	}
+}