[PATCH 2/5] crypto/sha1.c: avoid shifting count left and right

[Nicolas Pitre <nico@cam.org>]

This patch avoids shifting the count left and right needlessly for each
call to sha1_update().  It instead can be done only once at the end in
sha1_final().

Keeping the previous test example (sha1_update() successively called with
len=64), a 1.3% performance increase can be observed on i386, or 0.2% on
ARM.  The generated code is also smaller on ARM.

Signed-off-by: Nicolas Pitre <nico@cam.org>

Index: linux-2.6/crypto/sha1.c
===================================================================
--- linux-2.6.orig/crypto/sha1.c
+++ linux-2.6/crypto/sha1.c
@@ -51,8 +51,8 @@
 	unsigned int partial, done;
 	u32 temp[SHA_WORKSPACE_WORDS];
 
-	partial = (sctx->count >> 3) & 0x3f;
-	sctx->count += len << 3;
+	partial = sctx->count & 0x3f;
+	sctx->count += len;
 	done = 0;
 
 	if ((partial + len) > 63) {
@@ -80,7 +80,7 @@
 	u8 bits[8] = { 0, };
 	static const u8 padding[64] = { 0x80, };
 
-	t = sctx->count;
+	t = sctx->count << 3;
 	bits[7] = 0xff & t; t>>=8;
 	bits[6] = 0xff & t; t>>=8;
 	bits[5] = 0xff & t; t>>=8;
@@ -91,7 +91,7 @@
 	bits[0] = 0xff & t;
 
 	/* Pad out to 56 mod 64 */
-	index = (sctx->count >> 3) & 0x3f;
+	index = sctx->count & 0x3f;
 	padlen = (index < 56) ? (56 - index) : ((64+56) - index);
 	sha1_update(sctx, padding, padlen);