[PATCH]: fix 32bits integer overflow in loops_per_jiffy calculation

Yoann Vandoorselaere
2002-08-22T09:46:24Z

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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

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--- 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;
}