crypto: arc4 - improve performance by using u32 for ctx and variables

This patch changes u8 in struct arc4_ctx and variables to u32 (as AMD seems
to have problem with u8 array). Below are tcrypt results of old 1-byte block
cipher versus ecb(arc4) with u8 and ecb(arc4) with u32.

tcrypt results, x86-64 (speed ratios: new-u32/old, new-u8/old):

                  u32    u8
AMD Phenom II   : x3.6   x2.7
Intel Core 2    : x2.0   x1.9

tcrypt results, i386 (speed ratios: new-u32/old, new-u8/old):

                  u32    u8
Intel Atom N260 : x1.5   x1.4

Cc: Jon Oberheide <[email protected]>
Signed-off-by: Jussi Kivilinna <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>

crypto/arc4.c

@@ -22,8 +22,8 @@
 #define ARC4_BLOCK_SIZE		1
 
 struct arc4_ctx {
-	u8 S[256];
-	u8 x, y;
+	u32 S[256];
+	u32 x, y;
 };
 
 static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
@@ -39,7 +39,7 @@ static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
 		ctx->S[i] = i;
 
 	for (i = 0; i < 256; i++) {
-		u8 a = ctx->S[i];
+		u32 a = ctx->S[i];
 		j = (j + in_key[k] + a) & 0xff;
 		ctx->S[i] = ctx->S[j];
 		ctx->S[j] = a;
@@ -53,9 +53,9 @@ static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
 static void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in,
 		       unsigned int len)
 {
-	u8 *const S = ctx->S;
-	u8 x, y, a, b;
-	u8 ty, ta, tb;
+	u32 *const S = ctx->S;
+	u32 x, y, a, b;
+	u32 ty, ta, tb;
 
 	if (len == 0)
 		return;