division and cpu usage

Hello.

I'm new to kernel development and have some questions.

1. Why can't I divide with regular casting to double ((double)a /
(double)b)? It gives me strange errors when compiling:

WARNING: "__divdf3" [/root....] undefined!
WARNING: "__addf3" [/root/...] undefined!
WARNING: "__floatsidf" [/root/...] undefined!

And if I compile with normal integers, I get zero as the result.

2. I'm trying to get the percentage of CPU used for a certain
task_struct and figured the following formula:

(task->utime + task->stime) / jiffies

Before calculating I convert all the variables to jiffies. Is this correct?

Please help.

Greets,
Lukla
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