From: George Spelvin <linux@horizon.com>
Date: Fri, 28 Sep 2012 00:20:13 +0000 (+1000)
Subject: lib: vsprintf: optimize put_dec_trunc8()
X-Git-Tag: next-20120928~1^2~157
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=27c0b3bb49b3e76825e102f412eae85f6b2ae88c;p=karo-tx-linux.git

lib: vsprintf: optimize put_dec_trunc8()

If you're going to have a conditional branch after each 32x32->64-bit
multiply, might as well shrink the code and make it a loop.

This also avoids using the long multiply for small integers.

(This leaves the comments in a confusing state, but that's a separate
patch to make review easier.)

Signed-off-by: George Spelvin <linux@horizon.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 8cb7635b2ce3..f58fc4b1eaf0 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -174,20 +174,12 @@ char *put_dec_trunc8(char *buf, unsigned r)
 	unsigned q;
 
 	/* Copy of previous function's body with added early returns */
-	q      = (r * (uint64_t)0x1999999a) >> 32;
-	*buf++ = (r - 10 * q) + '0'; /* 2 */
-	if (q == 0)
-		return buf;
-	r      = (q * (uint64_t)0x1999999a) >> 32;
-	*buf++ = (q - 10 * r) + '0'; /* 3 */
-	if (r == 0)
-		return buf;
-	q      = (r * (uint64_t)0x1999999a) >> 32;
-	*buf++ = (r - 10 * q) + '0'; /* 4 */
-	if (q == 0)
-		return buf;
-	r      = (q * (uint64_t)0x1999999a) >> 32;
-	*buf++ = (q - 10 * r) + '0'; /* 5 */
+	while (r >= 10000) {
+		q = r + '0';
+		r  = (r * (uint64_t)0x1999999a) >> 32;
+		*buf++ = q - 10*r;
+	}
+
 	if (r == 0)
 		return buf;
 	q      = (r * 0x199a) >> 16;