linux-kernel - [patch 2.6.26-rc7] <linux/bcd.h> space reduction

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Date:	Sun, 22 Jun 2008 19:54:36 -0700
From:	David Brownell <david-b@...bell.net>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	rtc-linux@...glegroups.com
Subject: [patch 2.6.26-rc7] <linux/bcd.h> space reduction

This updates <linux/bcd.h> to define the key routines as static
constant functions, which the macros will then call.

In effect this lets each user of these BCD routines shrink their
codespace, when GCC observes that's a win, by using N function calls
and one copy of the routines, instead of N inlined copies of these
constant functions.

These routines aren't used in speed-critical code.  Almost all callers
are from the RTC framework.  Typical per-driver savings top 200 bytes.
On one RTC driver that's almost a 20% reduction in runtime I-space
footprint; for many, closer to 10%; for rtc-cmos it's about 4%.

Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net>
---
 include/linux/bcd.h |   16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

--- a/include/linux/bcd.h	2008-06-21 22:26:14.000000000 -0700
+++ b/include/linux/bcd.h	2008-06-21 22:37:48.000000000 -0700
@@ -10,8 +10,20 @@
 #ifndef _BCD_H
 #define _BCD_H

-#define BCD2BIN(val)	(((val) & 0x0f) + ((val)>>4)*10)
-#define BIN2BCD(val)	((((val)/10)<<4) + (val)%10)
+static int __bcd2bin(u8 val) __attribute_const__ __maybe_unused;
+static int __bcd2bin(u8 val)
+{
+	return (val & 0x0f) + (val >> 4) * 10;
+}
+
+static u8 __bin2bcd(unsigned val) __attribute_const__ __maybe_unused;
+static u8 __bin2bcd(unsigned val)
+{
+	return ((val/10) << 4) + val % 10;
+}
+
+#define BCD2BIN(val)	__bcd2bin(val)
+#define BIN2BCD(val)	__bin2bcd(val)

 /* backwards compat */
 #define BCD_TO_BIN(val) ((val)=BCD2BIN(val))
--
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