merge prefer_openssl package into stupidgcm

Now that I have discovered golang.org/x/sys/cpu and that Go
versions below 1.6 are uncommon, there was not much useful
code left in prefer_openssl.

Merge the remains into stupidgcm.

1 files changed, 26 insertions, 0 deletions

diff --git a/internal/stupidgcm/prefer.go b/internal/stupidgcm/prefer.go
new file mode 100644
index 0000000..a08d154
--- /dev/null
+++ b/internal/stupidgcm/prefer.go
@@ -0,0 +1,26 @@
+package stupidgcm
+
+import (
+	"golang.org/x/sys/cpu"
+)
+
+// PreferOpenSSL tells us if OpenSSL is faster than Go GCM on this machine.
+//
+// Go GCM is only faster if the CPU:
+//
+// 1) Is X86
+// 2) Has AES instructions
+// 3) Go is v1.6 or higher
+//
+// See https://github.com/rfjakob/gocryptfs/wiki/CPU-Benchmarks
+// for benchmarks.
+func PreferOpenSSL() bool {
+	if BuiltWithoutOpenssl {
+		return false
+	}
+	// Safe to call on other architectures - will just read false.
+	if cpu.X86.HasAES {
+		return false
+	}
+	return true
+}