x86: clean up computation of HPET .mult variables
While reading through the HPET code I realized that the
computation of .mult variables could be done with less
lines of code, resulting in a 1.6% text size saving
for hpet.o
So I propose the following patch, which applies against
today's Linus -git tree.
>From 0c6507e400e9ca5f7f14331e18f8c12baf75a9d3 Mon Sep 17 00:00:00 2001
From: Carlos R. Mafra <crmafra@ift.unesp.br>
Date: Mon, 5 May 2008 19:38:53 -0300
The computation of clocksource_hpet.mult
tmp = (u64)hpet_period << HPET_SHIFT;
do_div(tmp, FSEC_PER_NSEC);
clocksource_hpet.mult = (u32)tmp;
can be streamlined if we note that it is equal to
clocksource_hpet.mult = div_sc(hpet_period, FSEC_PER_NSEC, HPET_SHIFT);
Furthermore, the computation of hpet_clockevent.mult
uint64_t hpet_freq;
hpet_freq = 1000000000000000ULL;
do_div(hpet_freq, hpet_period);
hpet_clockevent.mult = div_sc((unsigned long) hpet_freq,
NSEC_PER_SEC, hpet_clockevent.shift);
can also be streamlined with the observation that hpet_period and hpet_freq are
inverse to each other (in proper units).
So instead of computing hpet_freq and using (schematically)
div_sc(hpet_freq, 10^9, shift) we use the trick of calling with the
arguments in reverse order, div_sc(10^6, hpet_period, shift).
The different power of ten is due to frequency being in Hertz (1/sec)
and the period being in units of femtosecond. Explicitly,
mult = (hpet_freq * 2^shift)/10^9 (before)
mult = (10^6 * 2^shift)/hpet_period (after)
because hpet_freq = 10^15/hpet_period.
The comments in the code are also updated to reflect the changes.
As a result,
text data bss dec hex filename
2957 425 92 3474 d92 arch/x86/kernel/hpet.o
3006 425 92 3523 dc3 arch/x86/kernel/hpet.o.old
a 1.6% reduction in text size.
Signed-off-by: Carlos R. Mafra <crmafra@ift.unesp.br>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
1 file changed
