From f4ae0304aff2f721ebe6088aa4f4c83f872f1ee9 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Tue, 8 Dec 2015 13:22:57 +0100
Subject: opensslGCM: preallocate buffer space, improves performance by 11%

Results of cryptfs/openssl_benchmark.bash :

Before:
  BenchmarkEnc_OpenSSL_4k_AES256_nonce96-2 	   50000	     31802 ns/op	 127.28 MB/s
  BenchmarkEnc_OpenSSL_4k_AES256_nonce128-2	   50000	     32110 ns/op	 126.06 MB/s

After:
  BenchmarkEnc_OpenSSL_4k_AES256_nonce96-2 	   50000	     28612 ns/op	 141.47 MB/s
  BenchmarkEnc_OpenSSL_4k_AES256_nonce128-2	   50000	     28613 ns/op	 141.47 MB/s
---
 cryptfs/openssl_aead.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/cryptfs/openssl_aead.go b/cryptfs/openssl_aead.go
index 1ec7c48..c70bd1f 100644
--- a/cryptfs/openssl_aead.go
+++ b/cryptfs/openssl_aead.go
@@ -25,7 +25,11 @@ func (be opensslGCM) NonceSize() int {
 // time, for a given key.
 func (be opensslGCM) Seal(dst, nonce, plaintext, data []byte) []byte {
 
-	cipherBuf := bytes.NewBuffer(dst)
+	// Preallocate output buffer
+	var cipherBuf bytes.Buffer
+	cipherBuf.Grow(len(dst) + len(plaintext) + AUTH_TAG_LEN)
+	// Output will be appended to dst
+	cipherBuf.Write(dst)
 
 	ectx, err := openssl.NewGCMEncryptionCipherCtx(KEY_LEN*8, nil, be.key, nonce)
 	if err != nil {
-- 
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