On 01/12/2015 02:25 PM, Pavel Machek wrote:
Hi!
+struct max77693_sub_led {
+ /* related FLED output identifier */
->flash LED, about 4x.
+/* split composite current @i into two @iout according to @imax weights */
+static void __max77693_calc_iout(u32 iout[2], u32 i, u32 imax[2])
+{
+ u64 t = i;
+
+ t *= imax[1];
+ do_div(t, imax[0] + imax[1]);
+
+ iout[1] = (u32)t / FLASH_IOUT_STEP * FLASH_IOUT_STEP;
+ iout[0] = i - iout[1];
+}
Is 64-bit arithmetics neccessary here? Could we do the FLASH_IOUT_STEP
divisons before t *=, so that 64-bit division is not neccessary?
It is required. All these operations allow for splitting the composite
current into both outputs according to weights given in the imax
array.
I know.
What about this?
static void __max77693_calc_iout(u32 iout[2], u32 i, u32 imax[2])
{
u32 t = i;
t *= imax[1] / FLASH_IOUT_STEP;
Let's consider following case:
t = 1000000
imax[1] = 1000000
multiplication of the above will give 10^12 - much more than
it is possible to encode on 32 bits.
t = t / (imax[0] + imax[1]);
t /= FLASH_IOUT_STEP
iout[1] = (u32)t;
iout[0] = i - iout[1];
}
Does it lack precision?
Thanks,
Pavel
--
Best Regards,
Jacek Anaszewski
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