Received: (at 21883) by debbugs.gnu.org; 15 Oct 2018 07:09:01 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Mon Oct 15 03:09:01 2018 Received: from localhost ([127.0.0.1]:49734 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1gBwzt-00030i-1P for submit <at> debbugs.gnu.org; Mon, 15 Oct 2018 03:09:01 -0400 Received: from mail-ua1-f41.google.com ([209.85.222.41]:43636) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <stefan.itampe@HIDDEN>) id 1gBwzq-00030O-1T for 21883 <at> debbugs.gnu.org; Mon, 15 Oct 2018 03:08:59 -0400 Received: by mail-ua1-f41.google.com with SMTP id c89so1644526uac.10 for <21883 <at> debbugs.gnu.org>; Mon, 15 Oct 2018 00:08:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=/qc5Ip8hNC/pcGnHbJP4W6ZUdi69jn1GEv96Av8wfxY=; b=ARxm1REjX0+RFLAmkeW+krcj1Pz6w1YeA4jUmb2YORQr1LLha3JyYoNgPebb00JRjT HyQUn/zxUsU0mJZVLLPIfpfaO80WrPPHYZMSU2A+vCnZ0kmGgg5pQdltTmrhekVUEufH tA0rrKj78zFWh0G3U+ypCp9/T8cP2FkNgbvlv243pI36ommcJA/oBVgwZnzLgX92ayiZ Vyxa3YQDjR1awgZ9ZFcciiuQc3vls31bFS6eM5hVxVPEU6j808qPVsXdAZji8wXD2dnh AzJEVg4FhXORw0HyAck/Gy+umtO6mx+qwHtSyoXwc0Mp4MDpDpP5i4XMWV41goMXMpiS R9yQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=/qc5Ip8hNC/pcGnHbJP4W6ZUdi69jn1GEv96Av8wfxY=; b=lrr42hqmaiBpj3Q19Ehsz2kxcqAf45TirKBbhg/PZIQnjGo12NuuWa82kQnMhxiLha XP3uUOMx0+apAZI9/qLBb04+qMQ+ldamN/ZnMZOpvBTOTeWlqSscdJ+uM8XWIg0t7uRi 3JXNm16Uq44Rvzx9N1yBvBVZaiNj++u/o8bIeLUVSV4FfK1tcHQG+sSGhNjLkWNY7di0 tpmr0VjGqG7RH78T56sNJP5FGxAsZ3ZvqaGWpEtxgdYalAfW5vJidnN13ZJN3I2U6KuT f66HstGlg94m0/HZT9w7tbSVLaHVPIYKLtudtpqpMigP5RioulOTrXt8ti3KCslFdrWa +6Jw== X-Gm-Message-State: ABuFfogjvIFdC5K+Ty6V5juH7YH9UskCIwFeVcGOYIEFTcwcepW4EWhy VwGepMBhXh7ggOsn64pq7+kGUwgHs504kAVkjFE= X-Google-Smtp-Source: ACcGV60rFSp9CvZYLeQN6M94d4UCur+v6tRqLB0oIHmIUrbBj59KywlEeLPuP7+ttOQE4sdImaj3hq2LRHswHnvnEyU= X-Received: by 2002:ab0:24a:: with SMTP id 68-v6mr6861456uas.25.1539587332448; Mon, 15 Oct 2018 00:08:52 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a1f:2801:0:0:0:0:0 with HTTP; Mon, 15 Oct 2018 00:08:51 -0700 (PDT) Received: by 2002:a1f:2801:0:0:0:0:0 with HTTP; Mon, 15 Oct 2018 00:08:51 -0700 (PDT) In-Reply-To: <87a7ngtblz.fsf@HIDDEN> References: <20151112070725.GA875@HIDDEN> <87tvlpszzu.fsf@HIDDEN> <CAGua6m1D3Ed-T3GJntfZr5QesTvR_Gf1-JbsiAetdoxBGkce_w@HIDDEN> <CAGua6m1CrfW2jEmQcDn_-1szGQbNcboBa45M6inEE5As6FToXw@HIDDEN> <CAGua6m1gnynxOxWsTEjf=EAMirWVp+bOP2aTsiLs=d1Z0UmdLw@HIDDEN> <87a7ngtblz.fsf@HIDDEN> From: Stefan Israelsson Tampe <stefan.itampe@HIDDEN> Date: Mon, 15 Oct 2018 09:08:51 +0200 Message-ID: <CAGua6m0iuBz3rSzYz_=NJD1a3KOEivdEQGF6VkYDq8GNaqCXKQ@HIDDEN> Subject: Re: bug#21883: unnecessary bit shifting range limits To: Mark H Weaver <mhw@HIDDEN> Content-Type: multipart/alternative; boundary="0000000000000d280605783f1ccc" X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 21883 Cc: 21883 <at> debbugs.gnu.org, Zefram <zefram@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.0 (-) --0000000000000d280605783f1ccc Content-Type: text/plain; charset="UTF-8" i think you got it. sorry for the fuzz. Den 15 okt 2018 12:19 AM skrev "Mark H Weaver" <mhw@HIDDEN>: > Stefan Israelsson Tampe <stefan.itampe@HIDDEN> writes: > > how would this slow down the code. just add the correction where you > > throw the exception which should be in a branch outside the hot path. > > If you have a suggestion that's simpler than what I did in commits > 011aec7e, 9448a078, and 1990aa91, and just as fast in the common cases, > feel free to propose a patch. The words above are insufficient. > > Mark > --0000000000000d280605783f1ccc Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"auto">i think you got it. sorry for the fuzz.<div dir=3D"auto">= <br></div></div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">D= en 15 okt 2018 12:19 AM skrev "Mark H Weaver" <<a href=3D"mail= to:mhw@HIDDEN">mhw@HIDDEN</a>>:<br type=3D"attribution"><blockqu= ote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc s= olid;padding-left:1ex">Stefan Israelsson Tampe <<a href=3D"mailto:stefan= .itampe@HIDDEN">stefan.itampe@HIDDEN</a>> writes:<br> > how would this slow down the code. just add the correction where you<b= r> > throw the exception which should be in a branch outside the hot path.<= br> <br> If you have a suggestion that's simpler than what I did in commits<br> 011aec7e, 9448a078, and 1990aa91, and just as fast in the common cases,<br> feel free to propose a patch.=C2=A0 The words above are insufficient.<br> <br> =C2=A0 =C2=A0 =C2=A0 Mark<br> </blockquote></div></div> --0000000000000d280605783f1ccc--
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From: Mark H Weaver <mhw@HIDDEN>
To: Stefan Israelsson Tampe <stefan.itampe@HIDDEN>
Subject: Re: bug#21883: unnecessary bit shifting range limits
References: <20151112070725.GA875@HIDDEN> <87tvlpszzu.fsf@HIDDEN>
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Stefan Israelsson Tampe <stefan.itampe@HIDDEN> writes:
> how would this slow down the code. just add the correction where you
> throw the exception which should be in a branch outside the hot path.
If you have a suggestion that's simpler than what I did in commits
011aec7e, 9448a078, and 1990aa91, and just as fast in the common cases,
feel free to propose a patch. The words above are insufficient.
Mark
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From: Stefan Israelsson Tampe <stefan.itampe@HIDDEN>
Date: Sun, 14 Oct 2018 11:46:12 +0200
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Subject: Re: bug#21883: unnecessary bit shifting range limits
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--000000000000e39c6605782d302f
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how would this slow down the code. just add the correction where you throw
the exception which should be in a branch outside the hot path.
Den 14 okt 2018 10:19 AM skrev "Mark H Weaver" <mhw@HIDDEN>:
Zefram <zefram@HIDDEN> writes:
> Not really outright bugs, but these responses are less than awesome:
>
> $ guile -c '(write (logbit? (ash 1 100) 123))'
> ERROR: Value out of range 0 to 18446744073709551615:
1267650600228229401496703205376
> $ guile -c '(write (ash 0 (ash 1 100)))'
> ERROR: Value out of range -9223372036854775808 to 9223372036854775807:
1267650600228229401496703205376
> $ guile -c '(write (ash 123 (ash -1 100)))'
> ERROR: Value out of range -9223372036854775808 to 9223372036854775807: -
1267650600228229401496703205376
>
> In all three cases, the theoretically-correct result of the expression
> is not only representable but easily computed.
Commit 011aec7e240ef987931548d90c53e6692c85d01c on the stable-2.2 branch
extends 'ash' and 'round-ash' to handle the easily computed cases of
huge shifts.
> The functions could be improved to avoid failing in these cases, by
> adding logic amounting to:
>
> (define (better-logbit? b v)
> (if (>= b (integer-length v)) (< v 0) (logbit? b v)))
>
> (define (better-ash v s)
> (cond
> ((= v 0) 0)
> ((<= s (- (integer-length v))) (if (< v 0) -1 0))
> (else (ash v s))))
Unfortunately, simple implementations like the ones above slow down the
common case with expensive checks that are rarely needed. The
aforementioned commit takes pains to avoid slowing down the common case,
but at the cost of extra code complexity.
In theory we could do something similar with many other procedures that
implement operations on bits and bit fields, but I wonder if it's worth
the extra complexity.
Mark
--000000000000e39c6605782d302f
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<div dir=3D"auto">how would this slow down the code. just add the correctio=
n where you throw the exception which should be in a branch outside the hot=
path.</div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">Den 1=
4 okt 2018 10:19 AM skrev "Mark H Weaver" <<a href=3D"mailto:m=
hw@HIDDEN">mhw@HIDDEN</a>>:<br type=3D"attribution"><blockquote =
class=3D"quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;paddi=
ng-left:1ex">Zefram <<a href=3D"mailto:zefram@HIDDEN">zefram@HIDDEN<=
/a>> writes:<br>
<br>
> Not really outright bugs, but these responses are less than awesome:<b=
r>
><br>
> $ guile -c '(write (logbit? (ash 1 100) 123))'<br>
> ERROR: Value out of range 0 to 18446744073709551615: 12676506002282294=
0149670320537<wbr>6<br>
> $ guile -c '(write (ash 0 (ash 1 100)))'<br>
> ERROR: Value out of range -9223372036854775808 to 9223372036854775807:=
126765060022822940149670320537<wbr>6<br>
> $ guile -c '(write (ash 123 (ash -1 100)))'<br>
> ERROR: Value out of range -9223372036854775808 to 9223372036854775807:=
-<wbr>126765060022822940149670320537<wbr>6<br>
><br>
> In all three cases, the theoretically-correct result of the expression=
<br>
> is not only representable but easily computed.<br>
<br>
Commit 011aec7e240ef987931548d90c53e6<wbr>692c85d01c on the stable-2.2 bran=
ch<br>
extends 'ash' and 'round-ash' to handle the easily computed=
cases of<br>
huge shifts.<br>
<br>
> The functions could be improved to avoid failing in these cases, by<br=
>
> adding logic amounting to:<br>
><br>
> (define (better-logbit? b v)<br>
>=C2=A0 =C2=A0(if (>=3D b (integer-length v)) (< v 0) (logbit? b v=
)))<br>
><br>
> (define (better-ash v s)<br>
>=C2=A0 =C2=A0(cond<br>
>=C2=A0 =C2=A0 =C2=A0((=3D v 0) 0)<br>
>=C2=A0 =C2=A0 =C2=A0((<=3D s (- (integer-length v))) (if (< v 0) =
-1 0))<br>
>=C2=A0 =C2=A0 =C2=A0(else (ash v s))))<br>
<br>
Unfortunately, simple implementations like the ones above slow down the<br>
common case with expensive checks that are rarely needed.=C2=A0 The<br>
aforementioned commit takes pains to avoid slowing down the common case,<br=
>
but at the cost of extra code complexity.<br>
<br>
In theory we could do something similar with many other procedures that<br>
implement operations on bits and bit fields, but I wonder if it's worth=
<br>
the extra complexity.<br>
<font color=3D"#888888"><br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0Mark<br>
<br>
<br>
<br>
</font></blockquote></div><br></div>
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From: Mark H Weaver <mhw@HIDDEN>
To: Zefram <zefram@HIDDEN>
Subject: Re: bug#21883: unnecessary bit shifting range limits
References: <20151112070725.GA875@HIDDEN>
Date: Sun, 14 Oct 2018 04:18:13 -0400
In-Reply-To: <20151112070725.GA875@HIDDEN> (Zefram's message of "Thu, 12 Nov
2015 07:07:25 +0000")
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Zefram <zefram@HIDDEN> writes:
> Not really outright bugs, but these responses are less than awesome:
>
> $ guile -c '(write (logbit? (ash 1 100) 123))'
> ERROR: Value out of range 0 to 18446744073709551615: 1267650600228229401496703205376
> $ guile -c '(write (ash 0 (ash 1 100)))'
> ERROR: Value out of range -9223372036854775808 to 9223372036854775807: 1267650600228229401496703205376
> $ guile -c '(write (ash 123 (ash -1 100)))'
> ERROR: Value out of range -9223372036854775808 to 9223372036854775807: -1267650600228229401496703205376
>
> In all three cases, the theoretically-correct result of the expression
> is not only representable but easily computed.
Commit 011aec7e240ef987931548d90c53e6692c85d01c on the stable-2.2 branch
extends 'ash' and 'round-ash' to handle the easily computed cases of
huge shifts.
> The functions could be improved to avoid failing in these cases, by
> adding logic amounting to:
>
> (define (better-logbit? b v)
> (if (>= b (integer-length v)) (< v 0) (logbit? b v)))
>
> (define (better-ash v s)
> (cond
> ((= v 0) 0)
> ((<= s (- (integer-length v))) (if (< v 0) -1 0))
> (else (ash v s))))
Unfortunately, simple implementations like the ones above slow down the
common case with expensive checks that are rarely needed. The
aforementioned commit takes pains to avoid slowing down the common case,
but at the cost of extra code complexity.
In theory we could do something similar with many other procedures that
implement operations on bits and bit fields, but I wonder if it's worth
the extra complexity.
Mark
bug-guile@HIDDEN:bug#21883; Package guile.
Full text available.
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Date: Thu, 12 Nov 2015 07:07:25 +0000
From: Zefram <zefram@HIDDEN>
To: bug-guile@HIDDEN
Subject: unnecessary bit shifting range limits
Message-ID: <20151112070725.GA875@HIDDEN>
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Not really outright bugs, but these responses are less than awesome:
$ guile -c '(write (logbit? (ash 1 100) 123))'
ERROR: Value out of range 0 to 18446744073709551615: 1267650600228229401496703205376
$ guile -c '(write (ash 0 (ash 1 100)))'
ERROR: Value out of range -9223372036854775808 to 9223372036854775807: 1267650600228229401496703205376
$ guile -c '(write (ash 123 (ash -1 100)))'
ERROR: Value out of range -9223372036854775808 to 9223372036854775807: -1267650600228229401496703205376
In all three cases, the theoretically-correct result of the expression
is not only representable but easily computed. The functions could be
improved to avoid failing in these cases, by adding logic amounting to:
(define (better-logbit? b v)
(if (>= b (integer-length v)) (< v 0) (logbit? b v)))
(define (better-ash v s)
(cond
((= v 0) 0)
((<= s (- (integer-length v))) (if (< v 0) -1 0))
(else (ash v s))))
-zefram
Zefram <zefram@HIDDEN>:bug-guile@HIDDEN.
Full text available.bug-guile@HIDDEN:bug#21883; Package guile.
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