Improve how our printk calls do_div by using constants.

The do_div code has a nice optimization in it when it is called with
constants. The current highly generalized use of it defeats those
optimizations and causes trouble on ARM, resulting in a complex and
buggy code path.

Since we only need to print in bases 8, 10, and 16, do a minor
restructuring of the code so that we call do_div with constants.
If you need base 2, print in base 16 and do it in your head. :-)

This fixes an ongoing problem with ARM, will not harm X86, and will
help PPC should we ever want to support it again.
Plus, I don't have to ever try to understand the div64 assembly and where
it's going wrong :-)

Change-Id: I6a480011916eb0834e05c5bb10909d83330fe797
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/2235
Tested-by: build bot (Jenkins)
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

1 files changed, 16 insertions, 2 deletions

diff --git a/src/console/vtxprintf.c b/src/console/vtxprintf.c
index 28c5a604e0..9de25845bd 100644
--- a/src/console/vtxprintf.c
+++ b/src/console/vtxprintf.c
@@ -69,8 +69,22 @@ static int number(void (*tx_byte)(unsigned char byte),
 	i = 0;
 	if (num == 0)
 		tmp[i++]='0';
-	else while (num != 0)
-		tmp[i++] = digits[do_div(num,base)];
+	else while (num != 0){
+		/* there are some nice optimizations in the
+		 * Macros-From-Hell that form the div64 code
+		 * *IF* you call it with a constant.
+		 * We're firmware, we only do bases
+		 * 8, 10, and 16. Let's be smart.
+		 * This greatly helps ARM, reduces the
+		 * code footprint at compile time, and does not hurt x86.
+		 */
+		if (base == 10)
+			tmp[i++] = digits[do_div(num,10)];
+		else if (base == 8)
+			tmp[i++] = digits[do_div(num,8)];
+		else /* sorry, you're out of choices */
+			tmp[i++] = digits[do_div(num,16)];
+	}
 	if (i > precision)
 		precision = i;
 	size -= precision;