linux-kernel - [PATCH 4/7] lib/random32.c: Use <asm/unaligned.h> instead of hand-rolling it

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Date:	7 Jun 2014 04:25:18 -0400
From:	"George Spelvin" <linux@...izon.com>
To:	davem@...emloft.net, dborkman@...hat.com, linux@...izon.com,
	shemminger@...l.org, tytso@....edu
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 4/7] lib/random32.c: Use <asm/unaligned.h> instead of hand-rolling it

The functions exist for a reason; the manual byte-at-a-time code
is unnecessarily slow (and bloated).

Signed-off-by: George Spelvin <linux@...izon.com>
---
 lib/random32.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/lib/random32.c b/lib/random32.c
index e8f3557b..eee60100 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -37,6 +37,7 @@
 #include <linux/jiffies.h>
 #include <linux/random.h>
 #include <linux/sched.h>
+#include <asm/unaligned.h>
 
 #ifdef CONFIG_RANDOM32_SELFTEST
 static void __init prandom_state_selftest(void);
@@ -97,25 +98,23 @@ EXPORT_SYMBOL(prandom_u32);
  */
 void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes)
 {
-	unsigned char *p = buf;
+	u8 *p = buf;
 	int i;
 
-	for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) {
-		u32 random = prandom_u32_state(state);
-		int j;
+	for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32))
+		put_unaligned_le32(prandom_u32_state(state), p+i);
 
-		for (j = 0; j < sizeof(u32); j++) {
-			p[i + j] = random;
-			random >>= BITS_PER_BYTE;
-		}
-	}
 	if (i < bytes) {
 		u32 random = prandom_u32_state(state);
 
-		for (; i < bytes; i++) {
-			p[i] = random;
-			random >>= BITS_PER_BYTE;
+		if (bytes & 2) {
+			put_unaligned_le16((u16)random, p+i);
+			if ((bytes & 1) == 0)
+				return;
+			i += 2;
+			random >>= 16;
 		}
+		p[i] = (u8)random;
 	}
 }
 EXPORT_SYMBOL(prandom_bytes_state);
-- 
2.0.0

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