GNU logs - #67022, boring messages

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Subject: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
Resent-From: Young Mo Kang <kym327@HIDDEN>
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Date: Thu, 9 Nov 2023 12:40:24 -0500
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 Content preview:  Hello, I have noticed that GNU Gzip's CRC32 calculation is
 the main bottleneck in decompression, and it can run significantly faster
 >60% if we replace it with crc32 function from zlib. I tested decompression
 speed of linux source code tar.gz file before and after replacing CRC32
 computation. On an AMD 7735HS system, I get 
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Hello,


I have noticed that GNU Gzip's CRC32 calculation is the main bottleneck 
in decompression, and it can run significantly faster >60% if we replace 
it with crc32 function from zlib.


I tested decompression speed of linux source code tar.gz file before and 
after replacing CRC32 computation. On an AMD 7735HS system, I get

GNU Gzip unmodified
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:05.11
GNU Gzip with CRC32 from zlib
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.16


And I saw even better performance improvement when tested on an Apple 
Silicon M1 system.

GNU Gzip unmodified
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:06.83
GNU Gzip with CRC32 from zlib
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.72


Since both GNU Gzip and zlib are written by the same authors, I was 
wondering if GNU Gzip can share zlib's CRC32 calculation and obtain this 
performance gain--I am not sure if there would be a license issue though.


The following bash script should reproduce the result

```

# download GNU Gzip and zlib
wget -O- https://ftp.gnu.org/gnu/gzip/gzip-1.13.tar.gz | tar xzf -
wget -O- https://zlib.net/zlib-1.3.tar.gz | tar xzf -

# download linux source code as a test file for decompression speed
wget -O- https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.6.1.tar.xz 
| xz -d | gzip > linux.tar.gz

# compile zlib
cd zlib-1.3
CFLAGS="-O2 -g" ./configure --static && make -j
cd ..

# compile GNU Gzip
cd gzip-1.13
CFLAGS="-O2 -g" ./configure && make -j

# measure decompression speed
/usr/bin/time -v ./gzip -d < ../linux.tar.gz > linux.tar 2> ../gzip1.time

# use crc32 from zlib
cat > util.diff << EOF
@@ -27,6 +27,7 @@
  #include <stdlib.h>
  #include <errno.h>

+#include "crc32.h"
  #include "tailor.h"
  #include "gzip.h"
  #include <dirname.h>
@@ -136,25 +137,14 @@ copy (int in, int out)
  ulg
  updcrc (uch const *s, unsigned n)
  {
-    register ulg c;         /* temporary variable */
-
-    if (s == NULL) {
-        c = 0xffffffffL;
-    } else {
-        c = crc;
-        if (n) do {
-            c = crc_32_tab[((int)c ^ (*s++)) & 0xff] ^ (c >> 8);
-        } while (--n);
-    }
-    crc = c;
-    return c ^ 0xffffffffL;       /* (instead of ~c for 64-bit machines) */
+    crc = crc32(crc, s, n);
  }

  /* Return a current CRC value.  */
  ulg
  getcrc ()
  {
-  return crc ^ 0xffffffffL;
+  return crc;
  }

  #ifdef IBM_Z_DFLTCC
EOF
patch < util.diff util.c

# create header file
cat > crc32.h << EOF
#pragma once

unsigned long  crc32(unsigned long crc, const unsigned char  *buf,
                             unsigned int len);
EOF

# copy crc32 object file from zlib
cp ../zlib-1.3/crc32.o .

# re-compile GNU Gzip
gcc -O2 -g -c util.c -Ilib
gcc -O2 -g *.o lib/libgzip.a -o gzip

# measure decompression speed
/usr/bin/time -v ./gzip -d < ../linux.tar.gz > linux.tar 2> ../gzip2.time

# print out time difference
cd ..
echo
echo "GNU Gzip unmodified"
grep Elapsed gzip1.time
echo "GNU Gzip with CRC32 from zlib"
grep Elapsed gzip2.time
```

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From: help-debbugs@HIDDEN (GNU bug Tracking System)
To: Young Mo Kang <kym327@HIDDEN>
Subject: bug#67022: Acknowledgement (Gzip decompression can be 60% faster
 using zlib's CRC32)
Message-ID: <handler.67022.B.16995516772928.ack <at> debbugs.gnu.org>
References: <95870740-74fc-4416-aad0-640c0eaf8832@HIDDEN>
X-Gnu-PR-Message: ack 67022
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Reply-To: 67022 <at> debbugs.gnu.org
Date: Thu, 09 Nov 2023 17:42:01 +0000

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Message sent to bug-gzip@HIDDEN:

Subject: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
Resent-From: Paul Eggert <eggert@HIDDEN>
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Resent-Date: Thu, 09 Nov 2023 18:34:02 +0000
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To: Young Mo Kang <kym327@HIDDEN>, 67022 <at> debbugs.gnu.org
Message-ID: <e703aea9-aa26-4b03-a20f-5d7b32ab3d44@HIDDEN>
Date: Thu, 9 Nov 2023 10:32:43 -0800
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From: Paul Eggert <eggert@HIDDEN>
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On 2023-11-09 09:40, Young Mo Kang wrote:
> Since both GNU Gzip and zlib are written by the same authors, I was 
> wondering if GNU Gzip can share zlib's CRC32 calculation and obtain this 
> performance gain--I am not sure if there would be a license issue though.

Shouldn't be a license issue. It's just a lack of time issue.

Message sent to bug-gzip@HIDDEN:

Subject: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
References: <95870740-74fc-4416-aad0-640c0eaf8832@HIDDEN>
In-Reply-To: <95870740-74fc-4416-aad0-640c0eaf8832@HIDDEN>
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I tried to implement this slice-by-8 CRC but couldn&#39;t do it the way I w=
anted - without bloated zlib tables and stuff. Maybe because I don&#39;t ge=
t what updcrc(), getcrc(), setcrc() are and what they actually do. The whol=
e program is magical, there is no way to find do_de/compress(), nor anythin=
g like that, so it was difficult to actually find relevant code. But anyway=
, for a start I manged to make `makecrcs8.c&#39; to generate CRCs lookup ta=
ble (attached).   Regards  wrotycz=0D

--10HRHLDDXTJVCSCNTBMDMJnhgwp
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<br><div>I tried to implement this slice-by-8 CRC but couldn't do it the wa=
y I wanted - without bloated zlib tables and stuff. Maybe because I don't g=
et what updcrc(), getcrc(), setcrc() are and what they actually do. The who=
le program is magical, there is no way to find do_de/compress(), nor anythi=
ng like that, so it was difficult to actually find relevant code. But anywa=
y, for a start I manged to make `makecrcs8.c' to generate CRCs lookup table=
 (attached).<br></div><div><br></div><div>Regards<br></div><div>wrotycz<br>=
</div><div><br></div><br>
--10HRHLDDXTJVCSCNTBMDMJnhgwp--

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Subject: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
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From: "Adler, Mark" <madler@HIDDEN>
Thread-Topic: bug#67022: Gzip decompression can be 60% faster using zlib's
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Thread-Topic: bug#67022: Gzip decompression can be 60% faster using zlib's
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> And, again, due to level of complexity in the code, I didn't check it. I =
have this quirk that I want to understand stuff I use, here I couldn't so I=
 didn't follow.
>=20
> I will check that braids thing when I find something about it.


The paper on braided CRCs is in the zlib distribution: doc/crc-doc.1.0.pdf =
.

I apologize for your nausea. I recommend Pepto Bismol.

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Re: bug#67022: Gzip decompression can be 60% faster using zlib&#39;s CRC32 =
   I tried to make that CRC-slice-by-8 happen but, as I miss something, may=
be you will get that right.  My guess the problem lies in all those negatio=
ns of crc (`(return) crc =3D crc ^ 0xffffffff;&#39;).   I prepared diff tha=
t does that, in more, less simple way. `crc32_8b...()&#39; should be in uti=
l.c, and crc32.h should only contain lookup table generated by `sample/make=
crc8.c&#39;, but until it works correctly it is in the header. Moving it to=
 corret place is the least of the problem.   I put the diff in paste as it&=
#39;s bit big to attach to email.   ~~~ bash  wget -Ogzip-1.13-crc328-2.dif=
f  paste.ee https://paste.ee/d/mkqTU/0  cd gzip-1.13  patch -p1 ../gzip-1.1=
3-crc328-2.diff  ~~~   Hope that will help to make it happen.=0D

--2CXTWVPKQEHQOSSMDMCSPnhgwp
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html; charset=UTF-8

<div>Re: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32=
<br></div><div><br></div><div><br></div><div>I tried to make that CRC-slice=
-by-8 happen but, as I miss something, maybe you will get that right.<br></=
div><div>My guess the problem lies in all those negations of crc (`(return)=
 crc =3D crc ^ 0xffffffff;').<br></div><div><br></div><div>I prepared diff =
that does that, in more, less simple way. `crc32_8b...()' should be in util=
.c, and crc32.h should only contain lookup table generated by `sample/makec=
rc8.c', but until it works correctly it is in the header. Moving it to corr=
et place is the least of the problem.<br></div><div><br></div><div>I put th=
e diff in paste as it's bit big to attach to email.<br></div><div><br></div=
><div>~~~ bash<br></div><div>wget -Ogzip-1.13-crc328-2.diff <a href=3D"http=
s://paste.ee/d/mkqTU/0">https://paste.ee/d/mkqTU/0</a><br></div><div>cd gzi=
p-1.13<br></div><div>patch -p1 ../gzip-1.13-crc328-2.diff<br></div><div>~~~=
<br></div><div><br></div><div>Hope that will help to make it happen.<br></d=
iv><div><br></div>
--2CXTWVPKQEHQOSSMDMCSPnhgwp--

Message sent to bug-gzip@HIDDEN:

X-Loop: help-debbugs@HIDDEN
Subject: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
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--2CXTWVPKQEHQOSSMDMCSPnhgwp
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Re: bug#67022: Gzip decompression can be 60% faster using zlib&#39;s CRC32 =
   I tried to make that CRC-slice-by-8 happen but, as I miss something, may=
be you will get that right.  My guess the problem lies in all those negatio=
ns of crc (`(return) crc =3D crc ^ 0xffffffff;&#39;).   I prepared diff tha=
t does that, in more, less simple way. `crc32_8b...()&#39; should be in uti=
l.c, and crc32.h should only contain lookup table generated by `sample/make=
crc8.c&#39;, but until it works correctly it is in the header. Moving it to=
 corret place is the least of the problem.   I put the diff in paste as it&=
#39;s bit big to attach to email.   ~~~ bash  wget -Ogzip-1.13-crc328-2.dif=
f  paste.ee https://paste.ee/d/mkqTU/0  cd gzip-1.13  patch -p1 ../gzip-1.1=
3-crc328-2.diff  ~~~   Hope that will help to make it happen.=0D

--2CXTWVPKQEHQOSSMDMCSPnhgwp
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html; charset=UTF-8

<div>Re: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32=
<br></div><div><br></div><div><br></div><div>I tried to make that CRC-slice=
-by-8 happen but, as I miss something, maybe you will get that right.<br></=
div><div>My guess the problem lies in all those negations of crc (`(return)=
 crc =3D crc ^ 0xffffffff;').<br></div><div><br></div><div>I prepared diff =
that does that, in more, less simple way. `crc32_8b...()' should be in util=
.c, and crc32.h should only contain lookup table generated by `sample/makec=
rc8.c', but until it works correctly it is in the header. Moving it to corr=
et place is the least of the problem.<br></div><div><br></div><div>I put th=
e diff in paste as it's bit big to attach to email.<br></div><div><br></div=
><div>~~~ bash<br></div><div>wget -Ogzip-1.13-crc328-2.diff <a href=3D"http=
s://paste.ee/d/mkqTU/0">https://paste.ee/d/mkqTU/0</a><br></div><div>cd gzi=
p-1.13<br></div><div>patch -p1 ../gzip-1.13-crc328-2.diff<br></div><div>~~~=
<br></div><div><br></div><div>Hope that will help to make it happen.<br></d=
iv><div><br></div>
--2CXTWVPKQEHQOSSMDMCSPnhgwp--

Message sent to bug-gzip@HIDDEN:

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Subject: bug#67022: Re: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
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&gt; Mr. Wrotycz,   Mr Adler, let&#39;s spare the formalities. That&#39;s a=
 nickname.   &gt; &gt; On Mar 13, 2024, at 6:14=E2=80=AFPM, wrotycz &lt; wr=
otycz@#$%...   I know it&#39;s a mail list but I would appreciate to not br=
oadcast my email to every (spam)bot on the web. Archive is publicly availab=
le and easily searchable by boys, so next time don&#39;t quote someone&#39;=
s email in the message.   &gt; I=E2=80=99m not sure what you mean by =E2=80=
=9Cbloated=E2=80=9D   I mean 600[kB] of crc32.h. I know, there is a lot of =
conditionals (compilation)=C2=A0 that make it much smaller in=C2=A0 resulti=
ng object, but the sheer size of it makes me nausea. I guess, there is only=
 one person that can understand flow of conditional directives in it. And c=
rc32_z() is even more complicated in this regard.   To illustrate the diffe=
rence between code of zlib and, what I consider comprehensible, compare cod=
e of xxhash and xxhash-clean.  I hope you understand.  &gt; for CRC-32 does=
 not use slice-by-8. It uses braids   I noticed the lookup table is &#39;up=
side down&#39; but didn&#39;t know that thing.  And, again, due to level of=
 complexity in the code, I didn&#39;t check it. I have this quirk that I wa=
nt to understand stuff I use, here I couldn&#39;t so I didn&#39;t follow.  =
 I will check that braids thing when I find something about it.   Regards=
=0D

--2BFWQBUCGESKIQYBNAWYWnhgwp
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<div>&gt; Mr. Wrotycz,<br></div><div><br></div><div>Mr Adler, let's spare t=
he formalities. That's a nickname.<br></div><div><br></div><div>&gt; &gt; O=
n Mar 13, 2024, at 6:14=E2=80=AFPM, wrotycz &lt; wrotycz@#$%...<br></div><d=
iv><br></div><div>I know it's a mail list but I would appreciate to not bro=
adcast my email to every (spam)bot on the web. Archive is publicly availabl=
e and easily searchable by boys, so next time don't quote someone's email i=
n the message.<br></div><div><br></div><div>&gt; I=E2=80=99m not sure what =
you mean by =E2=80=9Cbloated=E2=80=9D<br></div><div><br></div><div>I mean 6=
00[kB] of crc32.h. I know, there is a lot of conditionals (compilation)&nbs=
p; that make it much smaller in&nbsp; resulting object, but the sheer size =
of it makes me nausea. I guess, there is only one person that can understan=
d flow of conditional directives in it. And crc32_z() is even more complica=
ted in this regard.<br></div><div><br></div><div><div>To illustrate the dif=
ference between code of zlib and, what I consider comprehensible, compare c=
ode of xxhash and xxhash-clean.<br></div><div>I hope you understand.</div><=
/div><div><br></div><div>&gt; for CRC-32 does not use slice-by-8. It uses b=
raids<br></div><div><br></div><div>I noticed the lookup table is 'upside do=
wn' but didn't know that thing.<br></div><div>And, again, due to level of c=
omplexity in the code, I didn't check it. I have this quirk that I want to =
understand stuff I use, here I couldn't so I didn't follow.<br></div><div><=
br></div><div>I will check that braids thing when I find something about it=
.<br></div><div><br></div><div>Regards<br></div>
--2BFWQBUCGESKIQYBNAWYWnhgwp--

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&gt; The paper on braided CRCs is in the zlib distribution: doc/crc-doc.1.0=
.pdf   Thanks for a tip, I read that and now it&#39;s bit clearer to me.   =
 Maybe it is slightly faster, but I wouldn&#39;t bet dollars against nuts i=
t&#39;s exact in my case as 7zip-crc also uses slice-by-8 algorithm and is =
actually faster.  Despite that the question is how do I use zlib crc32()? I=
t doesn&#39;t give me correct result.   My &#39;rig&#39; is this:   ~~~  cr=
c =3D -1  while (buffer, length =3D read_data()):  =C2=A0=C2=A0=C2=A0 {  =
=C2=A0=C2=A0=C2=A0 crc =3D crcfunc(crc, buffer, length)  =C2=A0=C2=A0=C2=A0=
 }  crc =3D ~crc  ~~~   This doesn&#39;t work with `crc32_z();&#39;=0D

--2LACWDOYPYTFNECAIWGWYnhgwp
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<div>&gt; The paper on braided CRCs is in the zlib distribution: doc/crc-do=
c.1.0.pdf<br></div><div><br></div><div>Thanks for a tip, I read that and no=
w it's bit clearer to me.<br></div><div><br></div><div><br></div><div>Maybe=
 it is slightly faster, but I wouldn't bet dollars against nuts it's exact =
in my case as 7zip-crc also uses slice-by-8 algorithm and is actually faste=
r.<br></div><div>Despite that the question is how do I use zlib crc32()? It=
 doesn't give me correct result.<br></div><div><br></div><div>My 'rig' is t=
his:<br></div><div><br></div><div>~~~<br></div><div>crc =3D -1<br></div><di=
v>while (buffer, length =3D read_data()):<br></div><div>&nbsp;&nbsp;&nbsp; =
{<br></div><div>&nbsp;&nbsp;&nbsp; crc =3D crcfunc(crc, buffer, length)<br>=
</div><div>&nbsp;&nbsp;&nbsp; }<br></div><div>crc =3D ~crc<br></div><div>~~=
~<br></div><div><br></div><div>This doesn't work with `crc32_z();'<br></div=
><div><br></div>
--2LACWDOYPYTFNECAIWGWYnhgwp--

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&gt; The initial value returned by crc32(0L, Z_NULL, 0) is 0, not -1. And t=
here is no post inversion   That was it, thanks.=0D

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&gt; The initial value returned by crc32(0L, Z_NULL, 0) is 0, not -1. And t=
here is no post inversion<br><div><br></div><div>That was it, thanks.<br></=
div>
--2IHERQNYTMXACBASKFYMGnhgwp--

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--2JOBDJRPLFXSFEMKADXWWnhgwp
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&gt; current code in zlib for CRC-32 does not use slice-by-8. It uses braid=
s, which is faster.    It turns out not to be that fancy in gzip&#39;s harn=
ess.  It seems to be tiny bit faster than slice-by-8 during decompression b=
ut slower during compression; to the point of being on par with current Sar=
wate algorithm, or tiny bit faster (  paste.ee paste.ee/p/QeBKL  ).    Bene=
fits are not that unambiguous. Though I didn&#39;t make that slicing-by-8 (=
  paste.ee paste.ee/d/mkqTU/0  ) work with gzip properly, I would consider =
it in a context of application itself. If braids are faster with decompress=
ion, not much though, and slower with compression, then it would make sense=
 to weight it somehow in this context and asses fitness for this particular=
 application.    Either way, whichever algorithm would be chosen it still w=
ould make sense to generate crc table dynamically, when program starts. It =
takes, on my turtle computer, less than 10 us. Even rolled version. Unrolle=
d isn&#39;t much faster either (10%-20%).  Using already generated &#39;Sar=
wate&#39;s&#39; table=C2=A0 as a basis, halves that time.  That&#39;s imper=
ceptible differences. None is going to notice that, even with atomic clock.=
=0D

--2JOBDJRPLFXSFEMKADXWWnhgwp
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<div><br></div><div class=3D"nh_extra"><p>&gt; current code in zlib for CRC=
-32 does not use slice-by-8. It uses braids, which is faster.<br></p><div><=
br></div><div><br></div></div><div>It turns out not to be that fancy in gzi=
p's harness.<br></div><div>It seems to be tiny bit faster than slice-by-8 d=
uring decompression but slower during compression; to the point of being on=
 par with current Sarwate algorithm, or tiny bit faster ( <a href=3D"http:/=
/paste.ee/p/QeBKL">paste.ee/p/QeBKL</a> ).<br></div><div><br></div><div><br=
></div><div>Benefits are not that unambiguous. Though I didn't make that sl=
icing-by-8 ( <a href=3D"http://paste.ee/d/mkqTU/0">paste.ee/d/mkqTU/0</a> )=
 work with gzip properly, I would consider it in a context of application i=
tself. If braids are faster with decompression, not much though, and slower=
 with compression, then it would make sense to weight it somehow in this co=
ntext and asses fitness for this particular application.<br></div><div><br>=
</div><div><br></div><div>Either way, whichever algorithm would be chosen i=
t still would make sense to generate crc table dynamically, when program st=
arts. It takes, on my turtle computer, less than 10 us. Even rolled version=
. Unrolled isn't much faster either (10%-20%).<br></div><div>Using already =
generated 'Sarwate's' table&nbsp; as a basis, halves that time.<br></div><d=
iv>That's imperceptible differences. None is going to notice that, even wit=
h atomic clock.<br></div><div><br></div>
--2JOBDJRPLFXSFEMKADXWWnhgwp--

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Subject: Gzip decompression can be 60% faster using zlib's CRC32
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 Content preview:  Hello, I have noticed that GNU Gzip's CRC32 calculation is
 the main bottleneck in decompression, and it can run significantly faster
 >60% if we replace it with crc32 function from zlib. I tested decompression
 speed of linux source code tar.gz file before and after replacing CRC32
 computation. On an AMD 7735HS system, I get 
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Hello,


I have noticed that GNU Gzip's CRC32 calculation is the main bottleneck 
in decompression, and it can run significantly faster >60% if we replace 
it with crc32 function from zlib.


I tested decompression speed of linux source code tar.gz file before and 
after replacing CRC32 computation. On an AMD 7735HS system, I get

GNU Gzip unmodified
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:05.11
GNU Gzip with CRC32 from zlib
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.16


And I saw even better performance improvement when tested on an Apple 
Silicon M1 system.

GNU Gzip unmodified
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:06.83
GNU Gzip with CRC32 from zlib
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.72


Since both GNU Gzip and zlib are written by the same authors, I was 
wondering if GNU Gzip can share zlib's CRC32 calculation and obtain this 
performance gain--I am not sure if there would be a license issue though.


The following bash script should reproduce the result

```

# download GNU Gzip and zlib
wget -O- https://ftp.gnu.org/gnu/gzip/gzip-1.13.tar.gz | tar xzf -
wget -O- https://zlib.net/zlib-1.3.tar.gz | tar xzf -

# download linux source code as a test file for decompression speed
wget -O- https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.6.1.tar.xz 
| xz -d | gzip > linux.tar.gz

# compile zlib
cd zlib-1.3
CFLAGS="-O2 -g" ./configure --static && make -j
cd ..

# compile GNU Gzip
cd gzip-1.13
CFLAGS="-O2 -g" ./configure && make -j

# measure decompression speed
/usr/bin/time -v ./gzip -d < ../linux.tar.gz > linux.tar 2> ../gzip1.time

# use crc32 from zlib
cat > util.diff << EOF
@@ -27,6 +27,7 @@
  #include <stdlib.h>
  #include <errno.h>

+#include "crc32.h"
  #include "tailor.h"
  #include "gzip.h"
  #include <dirname.h>
@@ -136,25 +137,14 @@ copy (int in, int out)
  ulg
  updcrc (uch const *s, unsigned n)
  {
-    register ulg c;         /* temporary variable */
-
-    if (s == NULL) {
-        c = 0xffffffffL;
-    } else {
-        c = crc;
-        if (n) do {
-            c = crc_32_tab[((int)c ^ (*s++)) & 0xff] ^ (c >> 8);
-        } while (--n);
-    }
-    crc = c;
-    return c ^ 0xffffffffL;       /* (instead of ~c for 64-bit machines) */
+    crc = crc32(crc, s, n);
  }

  /* Return a current CRC value.  */
  ulg
  getcrc ()
  {
-  return crc ^ 0xffffffffL;
+  return crc;
  }

  #ifdef IBM_Z_DFLTCC
EOF
patch < util.diff util.c

# create header file
cat > crc32.h << EOF
#pragma once

unsigned long  crc32(unsigned long crc, const unsigned char  *buf,
                             unsigned int len);
EOF

# copy crc32 object file from zlib
cp ../zlib-1.3/crc32.o .

# re-compile GNU Gzip
gcc -O2 -g -c util.c -Ilib
gcc -O2 -g *.o lib/libgzip.a -o gzip

# measure decompression speed
/usr/bin/time -v ./gzip -d < ../linux.tar.gz > linux.tar 2> ../gzip2.time

# print out time difference
cd ..
echo
echo "GNU Gzip unmodified"
grep Elapsed gzip1.time
echo "GNU Gzip with CRC32 from zlib"
grep Elapsed gzip2.time
```




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Date: Mon, 10 Feb 2025 23:46:40 -0800
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Subject: Re: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
From: Paul Eggert <eggert@HIDDEN>
To: Young Mo Kang <kym327@HIDDEN>
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On 2023-11-09 10:32, Paul Eggert wrote:
> On 2023-11-09 09:40, Young Mo Kang wrote:
>> Since both GNU Gzip and zlib are written by the same authors, I was 
>> wondering if GNU Gzip can share zlib's CRC32 calculation and obtain 
>> this performance gain--I am not sure if there would be a license issue 
>> though.
> 
> Shouldn't be a license issue. It's just a lack of time issue.

Due to work by Sam Russell and others it looks like gzip now has faster 
CRC32 code on Savannah master, so closing this old bug report. See:

https://bugs.gnu.org/74927
https://bugs.gnu.org/74192


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Your bug report

#67022: Gzip decompression can be 60% faster using zlib's CRC32

which was filed against the gzip package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 67022 <at> debbugs.gnu.org.

--=20
67022: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=3D67022
GNU Bug Tracking System
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Subject: Re: bug#67022: Gzip decompression can be 60% faster using zlib's CRC32
From: Paul Eggert <eggert@HIDDEN>
To: Young Mo Kang <kym327@HIDDEN>
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On 2023-11-09 10:32, Paul Eggert wrote:
> On 2023-11-09 09:40, Young Mo Kang wrote:
>> Since both GNU Gzip and zlib are written by the same authors, I was 
>> wondering if GNU Gzip can share zlib's CRC32 calculation and obtain 
>> this performance gain--I am not sure if there would be a license issue 
>> though.
> 
> Shouldn't be a license issue. It's just a lack of time issue.

Due to work by Sam Russell and others it looks like gzip now has faster 
CRC32 code on Savannah master, so closing this old bug report. See:

https://bugs.gnu.org/74927
https://bugs.gnu.org/74192


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 Content preview:  Hello, I have noticed that GNU Gzip's CRC32 calculation is
 the main bottleneck in decompression, and it can run significantly faster
 >60% if we replace it with crc32 function from zlib. I tested decompression
 speed of linux source code tar.gz file before and after replacing CRC32
 computation. On an AMD 7735HS system, I get 
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Hello,


I have noticed that GNU Gzip's CRC32 calculation is the main bottleneck 
in decompression, and it can run significantly faster >60% if we replace 
it with crc32 function from zlib.


I tested decompression speed of linux source code tar.gz file before and 
after replacing CRC32 computation. On an AMD 7735HS system, I get

GNU Gzip unmodified
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:05.11
GNU Gzip with CRC32 from zlib
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.16


And I saw even better performance improvement when tested on an Apple 
Silicon M1 system.

GNU Gzip unmodified
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:06.83
GNU Gzip with CRC32 from zlib
     Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.72


Since both GNU Gzip and zlib are written by the same authors, I was 
wondering if GNU Gzip can share zlib's CRC32 calculation and obtain this 
performance gain--I am not sure if there would be a license issue though.


The following bash script should reproduce the result

```

# download GNU Gzip and zlib
wget -O- https://ftp.gnu.org/gnu/gzip/gzip-1.13.tar.gz | tar xzf -
wget -O- https://zlib.net/zlib-1.3.tar.gz | tar xzf -

# download linux source code as a test file for decompression speed
wget -O- https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.6.1.tar.xz 
| xz -d | gzip > linux.tar.gz

# compile zlib
cd zlib-1.3
CFLAGS="-O2 -g" ./configure --static && make -j
cd ..

# compile GNU Gzip
cd gzip-1.13
CFLAGS="-O2 -g" ./configure && make -j

# measure decompression speed
/usr/bin/time -v ./gzip -d < ../linux.tar.gz > linux.tar 2> ../gzip1.time

# use crc32 from zlib
cat > util.diff << EOF
@@ -27,6 +27,7 @@
  #include <stdlib.h>
  #include <errno.h>

+#include "crc32.h"
  #include "tailor.h"
  #include "gzip.h"
  #include <dirname.h>
@@ -136,25 +137,14 @@ copy (int in, int out)
  ulg
  updcrc (uch const *s, unsigned n)
  {
-    register ulg c;         /* temporary variable */
-
-    if (s == NULL) {
-        c = 0xffffffffL;
-    } else {
-        c = crc;
-        if (n) do {
-            c = crc_32_tab[((int)c ^ (*s++)) & 0xff] ^ (c >> 8);
-        } while (--n);
-    }
-    crc = c;
-    return c ^ 0xffffffffL;       /* (instead of ~c for 64-bit machines) */
+    crc = crc32(crc, s, n);
  }

  /* Return a current CRC value.  */
  ulg
  getcrc ()
  {
-  return crc ^ 0xffffffffL;
+  return crc;
  }

  #ifdef IBM_Z_DFLTCC
EOF
patch < util.diff util.c

# create header file
cat > crc32.h << EOF
#pragma once

unsigned long  crc32(unsigned long crc, const unsigned char  *buf,
                             unsigned int len);
EOF

# copy crc32 object file from zlib
cp ../zlib-1.3/crc32.o .

# re-compile GNU Gzip
gcc -O2 -g -c util.c -Ilib
gcc -O2 -g *.o lib/libgzip.a -o gzip

# measure decompression speed
/usr/bin/time -v ./gzip -d < ../linux.tar.gz > linux.tar 2> ../gzip2.time

# print out time difference
cd ..
echo
echo "GNU Gzip unmodified"
grep Elapsed gzip1.time
echo "GNU Gzip with CRC32 from zlib"
grep Elapsed gzip2.time
```




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