lkml.org 
[lkml]   [2002]   [Aug]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH]: fix 32bits integer overflow in loops_per_jiffy calculation
From
Date
Hi,

The "low_part * mult" multiplication of the old function may overflow a
32bits integer...

This patch both fix the overflow issue (tested with frequencies up to
20Ghz), and make the result of the function lose less precision.

Please apply,

--
Yoann Vandoorselaere, http://www.prelude-ids.org

"Programming is a race between programmers, who try and make more and
more idiot-proof software, and universe, which produces more and more
remarkable idiots. Until now, universe leads the race" -- R. Cook
--- linux-benh/kernel/cpufreq.c 2002-08-21 17:27:52.000000000 +0200
+++ linux-yoann/kernel/cpufreq.c 2002-08-22 11:27:09.000000000 +0200
@@ -78,14 +78,16 @@ static unsigned int cpufreq_
*/
static unsigned long scale(unsigned long old, u_int div, u_int mult)
{
- unsigned long low_part, high_part;
-
- high_part = old / div;
- low_part = (old % div) / 100;
- high_part *= mult;
- low_part = low_part * mult / div;
-
- return high_part + low_part * 100;
+ unsigned long val, carry = 0;
+
+ mult /= 100;
+ div /= 100;
+ val = old / div * mult;
+
+ carry = old % div;
+ carry = carry * mult / div;
+
+ return val + carry;
}

\
 
 \ /
  Last update: 2005-03-22 13:28    [W:0.053 / U:1.708 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site