From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id 7EDC948B42 for ; Wed, 3 Jan 2024 19:27:52 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 31EAB68CC5B; Wed, 3 Jan 2024 21:27:49 +0200 (EET) Received: from relay4-d.mail.gandi.net (relay4-d.mail.gandi.net [217.70.183.196]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id C656968C8C4 for ; Wed, 3 Jan 2024 21:27:42 +0200 (EET) Received: by mail.gandi.net (Postfix) with ESMTPSA id A018FE0003 for ; Wed, 3 Jan 2024 19:27:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=niedermayer.cc; s=gm1; t=1704310061; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=eMcMsI8Px0qMZLB41bRSk+RVxuiGzYUw3bEdu1JHSy4=; b=oSFUQdJQHpsCYeCazBobCpCCQP+q77nyinc1QFQE5YirBEovW8GYNsFRtBjxi9mmDsImHy ZF36xzgJyG243dzqErgFVxQWGmgDK1f+PKpQ9RsKQqfwoqlEUT8BjTfrcMnCU3/PBDCn+H t1x0B5jv9ysOdS7dA75NynwCEM+VIPPEB8NJHo2xSGhkgBZUFGCKDLqbRQHgY4CGOJ1StL sln/il0FxxrFi0rIzM6VTAn+kb6+369Hvo8hfKb5gLFxrfnvcq4zZn8egKKL3ahazG2FfO jVn8RhHbF4VVX+CtJIY+x0T/oP5P5A3iQM3sgQdCp5ZmMjx+NSq22iMf2UXt9w== Date: Wed, 3 Jan 2024 20:27:40 +0100 From: Michael Niedermayer To: FFmpeg development discussions and patches Message-ID: <20240103192740.GZ6420@pb2> References: <20240102022845.9916-1-michael@niedermayer.cc> MIME-Version: 1.0 In-Reply-To: X-GND-Sasl: michael@niedermayer.cc Subject: Re: [FFmpeg-devel] [PATCH] avutil/eval: Use integer for random() state X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Content-Type: multipart/mixed; boundary="===============4277003547366189375==" Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: --===============4277003547366189375== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="dXJXs/M7/ajzpbcK" Content-Disposition: inline --dXJXs/M7/ajzpbcK Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Jan 02, 2024 at 12:06:29PM +0100, Stefano Sabatini wrote: > On date Tuesday 2024-01-02 03:28:45 +0100, Michael Niedermayer wrote: > > rounding the 64bit integer state to double between each iteration > > causes a reduction in quality of the random number generator. > > For example its period drops from 2^64 to around 200 million > >=20 > > Signed-off-by: Michael Niedermayer > > --- > > libavutil/eval.c | 16 +++++++++++++--- > > 1 file changed, 13 insertions(+), 3 deletions(-) > >=20 > > diff --git a/libavutil/eval.c b/libavutil/eval.c > > index bad9e4ecb8d..89c61ba4bf5 100644 > > --- a/libavutil/eval.c > > +++ b/libavutil/eval.c > > @@ -55,6 +55,7 @@ typedef struct Parser { > > void *log_ctx; > > #define VARS 10 > > double *var; > > + uint64_t *var_uint64; > > } Parser; > > =20 > > static const AVClass eval_class =3D { > > @@ -173,6 +174,7 @@ struct AVExpr { > > } a; > > struct AVExpr *param[3]; > > double *var; > > + uint64_t *var_uint64; > > }; > > =20 > > static double etime(double v) > > @@ -230,9 +232,10 @@ static double eval_expr(Parser *p, AVExpr *e) > > } > > case e_random:{ > > int idx=3D av_clip(eval_expr(p, e->param[0]), 0, VARS-1); > > - uint64_t r=3D isnan(p->var[idx]) ? 0 : p->var[idx]; > > + uint64_t r=3D p->var_uint64[idx] ? p->var_uint64[idx] : (i= snan(p->var[idx]) ? 0 : p->var[idx]); > > r=3D r*1664525+1013904223; > > p->var[idx]=3D r; > > + p->var_uint64[idx]=3D r; > > return e->value * (r * (1.0/UINT64_MAX)); > > } > > case e_while: { > > @@ -319,7 +322,11 @@ static double eval_expr(Parser *p, AVExpr *e) > > case e_div: return e->value * (d2 ? (d / d2) : d * INF= INITY); > > case e_add: return e->value * (d + d2); > > case e_last:return e->value * d2; > > - case e_st : return e->value * (p->var[av_clip(d, 0, VA= RS-1)]=3D d2); > > + case e_st : { > > + int index =3D av_clip(d, 0, VARS-1); >=20 > > + p->var_uint64[index] =3D 0; >=20 > can't you set this to d2 and then in case e_random: >=20 > uint64_t r =3D isnan(p->var[idx]) ? 0 : p->var_uint64[idx]; >=20 > ? setting var_uint64[] to d2 would require us to check for non representable cases like outside 0..UINT64_MAX and NAN. We would have to do this for every st() even though very few actually get u= sed as seeds. So it would slow it down. if we set it to 0, then we only need to do these checks in the first call t= o random (or just require the user not to use random with such values) subsequent calls use integers and need not check the double value thx [...] --=20 Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB The day soldiers stop bringing you their problems is the day you have stopp= ed=20 leading them. They have either lost confidence that you can help or conclud= ed=20 you do not care. Either case is a failure of leadership. - Colin Powell --dXJXs/M7/ajzpbcK Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iF0EABEIAB0WIQSf8hKLFH72cwut8TNhHseHBAsPqwUCZZW1JgAKCRBhHseHBAsP q+3OAJwK8GcGe5EjlHJh18IMOB7CC8B+zgCglvYBamsQiQ4txcP7cCBlfHyuWZQ= =qH7U -----END PGP SIGNATURE----- --dXJXs/M7/ajzpbcK-- --===============4277003547366189375== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe". --===============4277003547366189375==--