Messages in this thread | | | Date | Tue, 26 Oct 2021 23:15:57 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v4 6/8] tracing/histogram: Optimize division by a power of 2 |
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On Tue, 26 Oct 2021 22:21:23 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> I'm sure there's an algorithm somewhere that can give as the real max.
You got me playing with this more ;-)
OK, I added the rounding in the wrong place. I found that we can make the max_div to be the same as the shift! The bigger the shift, the bigger the max!
mult = (1 << shift) / div; max_div = (1 << shift)
But the rounding needs to be with the mult / shift:
return (val * mult + ((1 << shift) - 1)) >> shift;
When val goes pass 1 << shift, then the error will be off by more than one.
-- Steve
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