digitalmars.D.bugs - [Issue 7181] New: Make bswap a recognized sequence, rather than an intrinsic
- d-bugmail puremagic.com (21/21) Dec 29 2011 http://d.puremagic.com/issues/show_bug.cgi?id=7181
- d-bugmail puremagic.com (13/19) Dec 29 2011 http://d.puremagic.com/issues/show_bug.cgi?id=7181
- d-bugmail puremagic.com (14/25) Dec 29 2011 http://d.puremagic.com/issues/show_bug.cgi?id=7181
- d-bugmail puremagic.com (21/21) Dec 29 2011 http://d.puremagic.com/issues/show_bug.cgi?id=7181
- d-bugmail puremagic.com (8/32) Dec 29 2011 http://d.puremagic.com/issues/show_bug.cgi?id=7181
- d-bugmail puremagic.com (22/22) Apr 16 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7181
http://d.puremagic.com/issues/show_bug.cgi?id=7181
Summary: Make bswap a recognized sequence, rather than an
intrinsic
Product: D
Version: D1 & D2
Platform: Other
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: DMD
AssignedTo: nobody puremagic.com
ReportedBy: clugdbug yahoo.com.au
--- Comment #0 from Don <clugdbug yahoo.com.au> 2011-12-29 02:15:03 PST ---
In the same way that abs, rol and ror are recognized, bswap(int x)
could be identified from:
( x << 24 ) | ( x << 8 ) & 0xff0000 | ( x >> 8 ) & 0xff00 | ( x >> 24 );
and this would be completely portable.
--
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
Dec 29 2011
d-bugmail puremagic.com
http://d.puremagic.com/issues/show_bug.cgi?id=7181
bearophile_hugs eml.cc changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bearophile_hugs eml.cc
--- Comment #1 from bearophile_hugs eml.cc 2011-12-29 04:21:37 PST ---
(In reply to comment #0)
In the same way that abs, rol and ror are recognized, bswap(int x)
could be identified from:
( x << 24 ) | ( x << 8 ) & 0xff0000 | ( x >> 8 ) & 0xff00 | ( x >> 24 );
and this would be completely portable.
Even if this pattern gets recognized and optimized, I suggest to keep a bswap
function in Phobos, to avoid writing all that bug-prone stuff (I'd like a
rol/ror function pair too in Phobos).
--
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
Dec 29 2011
http://d.puremagic.com/issues/show_bug.cgi?id=7181 --- Comment #2 from Don <clugdbug yahoo.com.au> 2011-12-29 09:29:47 PST --- (In reply to comment #1)(In reply to comment #0)Definitely. It would just change from: int bswap(int); /* intrinsic */ into int bswap(int x) { return ( x << 24 ) | ( x << 8 ) & 0xff0000 | ( x >> 8 ) & 0xff00 | ( x >> 24 ); } -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------In the same way that abs, rol and ror are recognized, bswap(int x) could be identified from: ( x << 24 ) | ( x << 8 ) & 0xff0000 | ( x >> 8 ) & 0xff00 | ( x >> 24 ); and this would be completely portable.Even if this pattern gets recognized and optimized, I suggest to keep a bswap function in Phobos, to avoid writing all that bug-prone stuff (I'd like a rol/ror function pair too in Phobos).
Dec 29 2011
http://d.puremagic.com/issues/show_bug.cgi?id=7181
Andrei Alexandrescu <andrei metalanguage.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |andrei metalanguage.com
--- Comment #3 from Andrei Alexandrescu <andrei metalanguage.com> 2011-12-29
12:23:38 PST ---
Wonder if other patterns would need to be figured as well, e.g.
auto p1 = cast(char*) &x;
int y = void;
auto p2 = cast(char*) &y;
p2[0] = p1[3];
p2[1] = p1[2];
p2[2] = p1[1];
p2[3] = p1[0];
Or (probably more realistically) patterns involving temporaries and 2
expressions:
auto y = ( x << 24 ) | ( x << 8 ) & 0xff0000;
y |= ( x >> 8 ) & 0xff00 | ( x >> 24 );
--
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
Dec 29 2011
http://d.puremagic.com/issues/show_bug.cgi?id=7181 --- Comment #4 from Andrei Alexandrescu <andrei metalanguage.com> 2011-12-29 12:25:27 PST --- (In reply to comment #2)(In reply to comment #1)I only now realized the meaning of this remark... took me some 10 minutes. Clever. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------(In reply to comment #0)Definitely. It would just change from: int bswap(int); /* intrinsic */ into int bswap(int x) { return ( x << 24 ) | ( x << 8 ) & 0xff0000 | ( x >> 8 ) & 0xff00 | ( x >> 24 ); }In the same way that abs, rol and ror are recognized, bswap(int x) could be identified from: ( x << 24 ) | ( x << 8 ) & 0xff0000 | ( x >> 8 ) & 0xff00 | ( x >> 24 ); and this would be completely portable.Even if this pattern gets recognized and optimized, I suggest to keep a bswap function in Phobos, to avoid writing all that bug-prone stuff (I'd like a rol/ror function pair too in Phobos).
Dec 29 2011
http://d.puremagic.com/issues/show_bug.cgi?id=7181
Walter Bright <bugzilla digitalmars.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bugzilla digitalmars.com
--- Comment #5 from Walter Bright <bugzilla digitalmars.com> 2012-04-16
02:17:30 PDT ---
The following is now recognized and replaced with bswap:
(p[0]<<24)|(p[1]<<16)|(p[2]<<8)|(p[3]<<0)
where p is a pointer to a ubyte. I realize that there are many, many ways to
write bswap, but this is the recognized one. (The operands to | can at least
appear in any order.)
Also,
(p[3]<<24)|(p[2]<<16)|(p[1]<<8)|(p[0]<<0)
is now recognized and replaced with *cast(uint*)p, at least for x86 byte
ordering.
What remains to be done is to provide such a body for core.bitop.bswap() and
remove bswap from the compiler intrinsics.
For reference:
http://commandcenter.blogspot.com/2012/04/byte-order-fallacy.html
--
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
Apr 16 2012