On Thu, Sep 19, 2019 at 04:06:18PM +0200, Rasmus Villemoes wrote:
The scheduler uses a (currently private) fixed_power_int() in its load average computation for computing powers of numbers 0 < x < 1 expressed as fixed-point numbers, which is also what we want here. But that requires the scale to be a power-of-2.
It feels like there is some rationale missing in the description here.
What is the benefit of replacing the explicit int_pow() with the implicit multiplications?
Daniel.
We could (and a following patch will) change to use a power-of-2 scale, but for a fixed small exponent of 3, there's no advantage in using repeated squaring.
Signed-off-by: Rasmus Villemoes linux@rasmusvillemoes.dk
drivers/video/backlight/pwm_bl.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 9252d51f31b9..aee6839e024a 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -179,7 +179,8 @@ static u64 cie1931(unsigned int lightness, unsigned int scale) if (lightness <= (8 * scale)) { retval = DIV_ROUND_CLOSEST(lightness * 10, 9033); } else {
retval = int_pow((lightness + (16 * scale)) / 116, 3);
retval = (lightness + (16 * scale)) / 116;retval *= retval * retval;-- 2.20.1