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* [Bug middle-end/50481] New: builtin to reverse the bit order
@ 2011-09-22 10:33 marc.glisse at normalesup dot org
2011-09-22 15:10 ` [Bug middle-end/50481] " paolo.carlini at oracle dot com
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: marc.glisse at normalesup dot org @ 2011-09-22 10:33 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Bug #: 50481
Summary: builtin to reverse the bit order
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: middle-end
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: marc.glisse@normalesup.org
It would be useful if gcc provided a builtin to reverse the order of the bits
(turn abcdefgh into hgfedcba) in objects of all sizes from a byte to an
unsigned long long.
According to Joseph: "Various processors have an instruction to reverse the bit
order in a word (ARMv6T2 and later have RBIT, for example, and C6X has BITR on
C64X and above)." This kind of bit manipulation also has various optimizations
depending on the architecture (mirroring a byte can be implemented using a
64bit multiplication). It is thus well suited to a builtin with different
platform-specific implementations.
Such a builtin could be used for instance for Bug 50160.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/50481] builtin to reverse the bit order
2011-09-22 10:33 [Bug middle-end/50481] New: builtin to reverse the bit order marc.glisse at normalesup dot org
@ 2011-09-22 15:10 ` paolo.carlini at oracle dot com
2011-09-23 15:47 ` devel@the-user.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: paolo.carlini at oracle dot com @ 2011-09-22 15:10 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Paolo Carlini <paolo.carlini at oracle dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2011-09-22
Ever Confirmed|0 |1
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/50481] builtin to reverse the bit order
2011-09-22 10:33 [Bug middle-end/50481] New: builtin to reverse the bit order marc.glisse at normalesup dot org
2011-09-22 15:10 ` [Bug middle-end/50481] " paolo.carlini at oracle dot com
@ 2011-09-23 15:47 ` devel@the-user.org
2012-03-29 10:51 ` ptim034 at gmail dot com
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: devel@the-user.org @ 2011-09-23 15:47 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Jonathan Schmidt-Dominé <devel@the-user.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |devel@the-user.org
--- Comment #1 from Jonathan Schmidt-Dominé <devel@the-user.org> 2011-09-23 15:30:33 UTC ---
Informative web-page listing some methods:
http://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith64BitsDiv
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/50481] builtin to reverse the bit order
2011-09-22 10:33 [Bug middle-end/50481] New: builtin to reverse the bit order marc.glisse at normalesup dot org
2011-09-22 15:10 ` [Bug middle-end/50481] " paolo.carlini at oracle dot com
2011-09-23 15:47 ` devel@the-user.org
@ 2012-03-29 10:51 ` ptim034 at gmail dot com
2021-11-05 13:37 ` f.boesing at gmx dot de
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: ptim034 at gmail dot com @ 2012-03-29 10:51 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Tim Parker <ptim034 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ptim034 at gmail dot com
--- Comment #2 from Tim Parker <ptim034 at gmail dot com> 2012-03-29 10:46:11 UTC ---
I totally don't understand what you talking about =_=
http://www.buyanessay.com/
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/50481] builtin to reverse the bit order
2011-09-22 10:33 [Bug middle-end/50481] New: builtin to reverse the bit order marc.glisse at normalesup dot org
` (2 preceding siblings ...)
2012-03-29 10:51 ` ptim034 at gmail dot com
@ 2021-11-05 13:37 ` f.boesing at gmx dot de
2022-10-25 12:26 ` carlo at gcc dot gnu.org
2023-10-02 11:17 ` xry111 at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: f.boesing at gmx dot de @ 2021-11-05 13:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Frank <f.boesing at gmx dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |f.boesing at gmx dot de
--- Comment #7 from Frank <f.boesing at gmx dot de> ---
Would be really useful to have this.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/50481] builtin to reverse the bit order
2011-09-22 10:33 [Bug middle-end/50481] New: builtin to reverse the bit order marc.glisse at normalesup dot org
` (3 preceding siblings ...)
2021-11-05 13:37 ` f.boesing at gmx dot de
@ 2022-10-25 12:26 ` carlo at gcc dot gnu.org
2023-10-02 11:17 ` xry111 at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: carlo at gcc dot gnu.org @ 2022-10-25 12:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Carlo Wood <carlo at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |carlo at gcc dot gnu.org
--- Comment #8 from Carlo Wood <carlo at gcc dot gnu.org> ---
Bump - I need this too ;)
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/50481] builtin to reverse the bit order
2011-09-22 10:33 [Bug middle-end/50481] New: builtin to reverse the bit order marc.glisse at normalesup dot org
` (4 preceding siblings ...)
2022-10-25 12:26 ` carlo at gcc dot gnu.org
@ 2023-10-02 11:17 ` xry111 at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: xry111 at gcc dot gnu.org @ 2023-10-02 11:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Xi Ruoyao <xry111 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |xry111 at gcc dot gnu.org
--- Comment #9 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Useful for LoongArch too. And now we already have bitreverse RTX code since
r14-1586.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2023-10-02 11:17 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-09-22 10:33 [Bug middle-end/50481] New: builtin to reverse the bit order marc.glisse at normalesup dot org
2011-09-22 15:10 ` [Bug middle-end/50481] " paolo.carlini at oracle dot com
2011-09-23 15:47 ` devel@the-user.org
2012-03-29 10:51 ` ptim034 at gmail dot com
2021-11-05 13:37 ` f.boesing at gmx dot de
2022-10-25 12:26 ` carlo at gcc dot gnu.org
2023-10-02 11:17 ` xry111 at gcc dot gnu.org
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