[v2,3/4] backlight: pwm_bl: drop use of int_pow()
diff mbox series

Message ID 20191008120327.24208-4-linux@rasmusvillemoes.dk
State New
Headers show
Series
  • backlight: pwm_bl: optimizations and small fix for cie1913
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Commit Message

Rasmus Villemoes Oct. 8, 2019, 12:03 p.m. UTC
For a fixed small exponent of 3, it is more efficient to simply use
two explicit multiplications rather than calling the int_pow() library
function: Aside from the function call overhead, its implementation
using repeated squaring means it ends up doing four 64x64
multiplications.

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 drivers/video/backlight/pwm_bl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Lee Jones Oct. 14, 2019, 7:27 a.m. UTC | #1
On Tue, 08 Oct 2019, Rasmus Villemoes wrote:

> For a fixed small exponent of 3, it is more efficient to simply use
> two explicit multiplications rather than calling the int_pow() library
> function: Aside from the function call overhead, its implementation
> using repeated squaring means it ends up doing four 64x64
> multiplications.
> 
> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
>  drivers/video/backlight/pwm_bl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Applied, thanks.

Patch
diff mbox series

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 672c5e7cfcd1..273d3fb628a0 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;
 		retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
 	}