digitalmars.D.bugs - [Issue 5728] New: "rol" in core.bitop
- d-bugmail puremagic.com (79/79) Mar 10 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5728
- d-bugmail puremagic.com (9/9) Jul 28 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5728
- d-bugmail puremagic.com (13/13) Aug 03 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5728
- d-bugmail puremagic.com (12/12) Aug 03 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5728
- d-bugmail puremagic.com (27/27) Aug 07 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5728
- d-bugmail puremagic.com (8/12) Aug 09 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5728
- d-bugmail puremagic.com (14/16) Aug 09 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5728
http://d.puremagic.com/issues/show_bug.cgi?id=5728
Summary: "rol" in core.bitop
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: DMD
AssignedTo: nobody puremagic.com
ReportedBy: bearophile_hugs eml.cc
I'd like the "rol" X86 instrinsic added to core.bitop module.
--------------------
Rationale:
I'd like the intrinsic because rotating bits in a 32 bit number is a common
enough operation (there was recently a thread in D.learn of a person in need
for the fastest rotation of the bytes of a uint), and in C-derived languages
there isn't a bitwise operator for it, while most CPUs have four or more
instructions to rotate a register.
In C-like languages the problem is sometimes solved making the compiler a bit
smarter, but this little test shows DMD is not able to optimize two shifts plus
or into a single rot instruction:
dmd -O -release -inline test.d
int main(string[] args) {
uint x = args.length;
return (x << 24) | (x >> 8);
}
__Dmain comdat
mov EAX,4[ESP]
mov ECX,4[ESP]
shl EAX,018h
shr ECX,8
or EAX,ECX
ret
--------------------
Using inline asm is an option:
int main(string[] args) {
uint x = args.length;
asm {
rol x, 8;
}
return x;
}
__Dmain comdat
push EBP
mov EBP,ESP
push EAX
mov EAX,8[EBP]
mov -4[EBP],EAX
rol -4[EBP],8
mov EAX,-4[EBP]
mov ESP,EBP
pop EBP
ret
-----------------
But in some cases the inline gives problems, so I think an inlined intrinsic is
more handy, safer, shorter, simpler to use:
union Four {
uint u;
ubyte[4] a;
}
void main() {
Four f;
asm {
rol f.u, 8;
}
}
test.d(8): bad type/size of operands 'f.u'
-----------------
Note: an alternative to the intrinsic is to introduce in D/DMD a standard
syntax for inlined asm expressions using __asm(), as present in LDC, but they
are quite less easy to use than a rot() function-like intrinsic (but they are
much more useful than a single intrinsic):
http://www.dsource.org/projects/ldc/wiki/InlineAsmExpressions
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Mar 10 2011
d-bugmail puremagic.com http://d.puremagic.com/issues/show_bug.cgi?id=5728 Now DMD too is able to figure by itself when a rol is needed, but I think I'd like the instrinsic still: https://github.com/D-Programming-Language/dmd/commit/32ea0206dead162f564689339b6c43212042643c https://github.com/D-Programming-Language/dmd/commit/25df0466ab3ed9d36c354da7576e39f0c64663a5 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 28 2011
http://d.puremagic.com/issues/show_bug.cgi?id=5728
Adam D. Ruppe <destructionator gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |destructionator gmail.com
19:18:02 PDT ---
I just want to say that dmd commit is fantastic. We got a little embarrassed by
that in a discussion a couple weeks ago!
Re bearophiles request: it probably doesn't need an intrinsic since the
optimzation should let a plain library function do it just as well.
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Aug 03 2011
http://d.puremagic.com/issues/show_bug.cgi?id=5728
Walter Bright <bugzilla digitalmars.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |bugzilla digitalmars.com
Resolution| |FIXED
22:45:51 PDT ---
Adam's right.
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Aug 03 2011
http://d.puremagic.com/issues/show_bug.cgi?id=5728
As reference, DMD 2.055head compiles this D2 function:
T rot(T)(T x, int shift) {
return (x >> shift) | (x << (T.sizeof * 8 - shift));
}
void main() {
int a = 0b_1111_1111;
int b = 0b_0000_0010;
rot(a, b);
}
To (-O -release):
_D4test10__T3rotTiZ3rotFiiZi comdat
push EAX
mov EAX,8[ESP]
mov ECX,[ESP]
sar EAX,CL
mov ECX,020h
mov EDX,8[ESP]
sub ECX,[ESP]
shl EDX,CL
or EAX,EDX
pop ECX
ret 4
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Aug 07 2011
http://d.puremagic.com/issues/show_bug.cgi?id=5728
17:34:51 PDT ---
As reference, DMD 2.055head compiles this D2 function:
T rot(T)(T x, int shift) {
return (x >> shift) | (x << (T.sizeof * 8 - shift));
}
The mistake is this is not a correct rotate function. (x >> shift) is a signed
right shift. Rewrite as (x >>> shift).
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Aug 09 2011
http://d.puremagic.com/issues/show_bug.cgi?id=5728The mistake is this is not a correct rotate function. (x >> shift) is a signed right shift. Rewrite as (x >>> shift).Thank you, I'm wrong all the time. Now it shows the ror: _D4test10__T3rotTiZ3rotFNaNbxixiZi push EAX mov EAX,8[ESP] mov ECX,[ESP] ror EAX,CL pop ECX ret 4 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Aug 09 2011