From: Ira W. Snyder <devel@irasnyder.com>
Date: Mon, 22 Oct 2007 17:46:26 +0000 (-0700)
Subject: Const-ify Nb, Nk, Nr
X-Git-Tag: optimized~2
X-Git-Url: https://www.irasnyder.com/gitweb/?a=commitdiff_plain;h=f06d505218bd3f8c05e9c64f0705bfa3066f665c;p=aes.git

Const-ify Nb, Nk, Nr

This nets a little bit (~1.5%) of performance and makes all of the routines
a little more safe by making sure that class constants cannot be changed
except in the constructor.

Signed-off-by: Ira W. Snyder <devel@irasnyder.com>
---

diff --git a/aes.cpp b/aes.cpp
index e4aef0b..883d3b3 100644
--- a/aes.cpp
+++ b/aes.cpp
@@ -9,8 +9,7 @@ static byte xtimes (const byte bx);
 static void printState (byteArray &bytes, std::string name);
 
 AES::AES (const byteArray& key)
-	: Nb(4)					// This is constant in AES
-	, Nk(key.size() / 4)	// This can be either 4, 6, or 8 (128, 192, or 256 bit)
+	: Nk(key.size() / 4)	// This can be either 4, 6, or 8 (128, 192, or 256 bit)
 	, Nr(Nk + Nb + 2)
 	, keySchedule(Nb * (Nr+1), 0x00000000)
 {
diff --git a/aes.hpp b/aes.hpp
index 43808d4..5d2acd8 100644
--- a/aes.hpp
+++ b/aes.hpp
@@ -29,9 +29,21 @@ class AES
 		byteArray decrypt (const byteArray& ciphertext) const;
 
 	private:
-		unsigned int Nb;
-		unsigned int Nk;
-		unsigned int Nr;
+		/* Block size in words -- Always constant in AES.
+		 *
+		 * We also might as well make this static and share it between
+		 * all instances of AES. */
+		static const unsigned int Nb = 4;
+
+		/* Key size in words -- can be 4, 6, or 8.
+		 *
+		 * Once it is set by the constructor, it will never change */
+		const unsigned int Nk;
+
+		/* Number of rounds -- depends on key size.
+		 *
+		 * Once it is set by the constructor, it will never change */
+		const unsigned int Nr;
 
 		wordArray keySchedule;