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Message-ID: <8017042b74a05df72a7ebfb5ec21fc7cc088ed4e.camel@sipsolutions.net>
Subject: Re: [PATCH 2/2] mac80211: minstrel_ht: replace rate stats ewma with
 a better moving average
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Felix Fietkau <nbd@nbd.name>, linux-wireless@vger.kernel.org
Date:   Tue, 01 Oct 2019 13:06:18 +0200
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On Tue, 2019-10-01 at 12:52 +0200, Felix Fietkau wrote:
> 
> Might be useful, yes. The main issue here is that the period / window
> size has to be hardcoded through the coefficient values, unless we find
> a way to do floating point math, including exp() and cos() at compile
> time, including conversion to fixed point.

Works fine for me?

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#define E(x) ((int)(exp(x) * (1<<20)))
#define C(x) ((int)(cos(x) * (1<<20)))

int main()
{
        int e2 = E(2);
        int c2 = C(2);

        printf("e2: %d\n", e2);
        printf("whole: %d frac: %d\n", e2 >> 20, e2 & ((1 << 20) - 1));
        printf("c2: %d\n", c2);
        printf("sign: %s whole: %d frac: %d\n", c2 < 0 ? "-" : "", abs(c2) >> 20, abs(c2) & ((1 << 20) - 1));
}

objdump -dr test:
[...]
0000000000401040 <main>:
  401040:	48 83 ec 08          	sub    $0x8,%rsp
  401044:	be 92 39 76 00       	mov    $0x763992,%esi		// exp(2) * (1<<20)
  401049:	bf 10 20 40 00       	mov    $0x402010,%edi
  40104e:	31 c0                	xor    %eax,%eax
  401050:	e8 db ff ff ff       	callq  401030 <printf@plt>
  401055:	ba 92 39 06 00       	mov    $0x63992,%edx
  40105a:	be 07 00 00 00       	mov    $0x7,%esi
  40105f:	31 c0                	xor    %eax,%eax
  401061:	bf 2b 20 40 00       	mov    $0x40202b,%edi
  401066:	e8 c5 ff ff ff       	callq  401030 <printf@plt>
  40106b:	be 77 57 f9 ff       	mov    $0xfff95777,%esi
  401070:	bf 18 20 40 00       	mov    $0x402018,%edi
  401075:	31 c0                	xor    %eax,%eax
  401077:	e8 b4 ff ff ff       	callq  401030 <printf@plt>
  40107c:	b9 89 a8 06 00       	mov    $0x6a889,%ecx		// cos(2) * (1<<20)
  401081:	31 d2                	xor    %edx,%edx
  401083:	31 c0                	xor    %eax,%eax
  401085:	be 20 20 40 00       	mov    $0x402020,%esi
  40108a:	bf 22 20 40 00       	mov    $0x402022,%edi
  40108f:	e8 9c ff ff ff       	callq  401030 <printf@plt>
[...]

johannes