Re: Bug? 0 is less than -10
On Thursday, 8 October 2015 at 09:01:32 UTC, Dominikus Dittes
Scherkl wrote:
On Wednesday, 7 October 2015 at 16:25:02 UTC, Marc Schütz wrote:
Lionello Lunesu posted a PR that should fix this:
https://github.com/D-Programming-Language/dmd/pull/1913
See also the discussion in the linked bug report.
Unfortunately it seems it's been forgotten since then...
Meanwhile I have even improved my solution posted to fix bug
#259 to use less casts:
int opCmp(T, U)(const(T) a, const(U) b) pure @safe @nogc nothrow
if(isIntegral!T && isIntegral!U && !is(Unqual!T == Unqual!U))
{
static if(isSigned!T && isUnsigned!U && T.sizeof <= U.sizeof)
...
And on comparison with number literals everything will be
optimized away, so no execution timer overhead at all!
I like your solution! +1
Re: Bug? 0 is less than -10
On Wednesday, 7 October 2015 at 16:25:02 UTC, Marc Schütz wrote:
Lionello Lunesu posted a PR that should fix this:
https://github.com/D-Programming-Language/dmd/pull/1913
See also the discussion in the linked bug report.
Unfortunately it seems it's been forgotten since then...
Meanwhile I have even improved my solution posted to fix bug #259
to use less casts:
int opCmp(T, U)(const(T) a, const(U) b) pure @safe @nogc nothrow
if(isIntegral!T && isIntegral!U && !is(Unqual!T == Unqual!U))
{
static if(isSigned!T && isUnsigned!U && T.sizeof <= U.sizeof)
{
return (a < 0) ? -1 : opCmp(cast(U)a, b);
}
else static if(isUnsigned!T && isSigned!U && T.sizeof >=
U.sizeof)
{
return (b < 0) ? 1 : opCmp(a, cast(T)b);
}
else // both signed or both unsigned or the unsigned type is
smaller
{
// do what the compiler always did so far:
alias C = CommonType!(T, U); // use the larger of the both
return opCmp(cast(C)a, cast(C)b);
}
}
And on comparison with number literals everything will be
optimized away, so no execution timer overhead at all!
Re: Bug? 0 is less than -10
On 10/7/15 1:27 AM, Laeeth Isharc wrote: On Wednesday, 7 October 2015 at 02:53:32 UTC, Steven Schveighoffer wrote: On 10/6/15 7:21 PM, Laeeth Isharc wrote: could we have ssize_t defined in phobos somewhere so your code ends up being portable ;) (It's trivial to do, obviously). ptrdiff_t It seems unnatural to use such a name when the variable has nothing to do with pointers - it doesn't contribute to the readability. Yes, it's trivial, but small things cumulatively matter. Adam tends to use int and when that gets mixed up with an auto size_t (eg via length) then his code doesn't compile on 64 bit. And if it happens with his code, you can imagine this isn't a problem that inexperienced users never encounter. ptrdiff_t is in the C spec, ssize_t is not. No reason to name all the types of snow here. A machine-word-sized signed integer is ptrdiff_t. -Steve
Re: Bug? 0 is less than -10
On Thursday, 8 October 2015 at 13:32:17 UTC, Steven Schveighoffer wrote: On 10/7/15 1:27 AM, Laeeth Isharc wrote: On Wednesday, 7 October 2015 at 02:53:32 UTC, Steven Schveighoffer wrote: On 10/6/15 7:21 PM, Laeeth Isharc wrote: could we have ssize_t defined in phobos somewhere so your code ends up being portable ;) (It's trivial to do, obviously). ptrdiff_t It seems unnatural to use such a name when the variable has nothing to do with pointers - it doesn't contribute to the readability. Yes, it's trivial, but small things cumulatively matter. Adam tends to use int and when that gets mixed up with an auto size_t (eg via length) then his code doesn't compile on 64 bit. And if it happens with his code, you can imagine this isn't a problem that inexperienced users never encounter. ptrdiff_t is in the C spec, ssize_t is not. No reason to name all the types of snow here. A machine-word-sized signed integer is ptrdiff_t. -Steve Whatever - it's not that important to me. D isn't C, and has learnt from C's mistakes and infelicities. I love the beauty of C, but I'm glad I don't need to do my work in it. One reason why D is under appreciated is that these seemingly small differences make a big difference in practice, even if in theory they shouldn't. Initially I was quite offended by no loop aliasing. Until I saw how much time it saved me in avoiding silly mistakes. But really there are better things to worry about at the moment. Laeeth.
Re: Bug? 0 is less than -10
On Wednesday, 7 October 2015 at 05:27:12 UTC, Laeeth Isharc wrote: On Wednesday, 7 October 2015 at 02:53:32 UTC, Steven Schveighoffer wrote: On 10/6/15 7:21 PM, Laeeth Isharc wrote: could we have ssize_t defined in phobos somewhere so your code ends up being portable ;) (It's trivial to do, obviously). ptrdiff_t -Steve It seems unnatural to use such a name when the variable has nothing to do with pointers - it doesn't contribute to the readability. Yes, it's trivial, but small things cumulatively matter. Adam tends to use int and when that gets mixed up with an auto size_t (eg via length) then his code doesn't compile on 64 bit. And if it happens with his code, you can imagine this isn't a problem that inexperienced users never encounter. IMO it seems unnatural to use size_t with a signed/negative value too.
Re: Bug? 0 is less than -10
On Wednesday, 7 October 2015 at 07:38:44 UTC, Andrea Fontana wrote: On Wednesday, 7 October 2015 at 05:27:12 UTC, Laeeth Isharc wrote: On Wednesday, 7 October 2015 at 02:53:32 UTC, Steven Schveighoffer wrote: On 10/6/15 7:21 PM, Laeeth Isharc wrote: could we have ssize_t defined in phobos somewhere so your code ends up being portable ;) (It's trivial to do, obviously). ptrdiff_t -Steve It seems unnatural to use such a name when the variable has nothing to do with pointers - it doesn't contribute to the readability. Yes, it's trivial, but small things cumulatively matter. Adam tends to use int and when that gets mixed up with an auto size_t (eg via length) then his code doesn't compile on 64 bit. And if it happens with his code, you can imagine this isn't a problem that inexperienced users never encounter. IMO it seems unnatural to use size_t with a signed/negative value too. Indeed. But you end up with an inferred size_t in a foreach and using length with auto, so it makes sense to have something nicer that you can specify that won't make your code look strange. Doesn't bother me since I define ssize_t, but it might make D easier to read for others. When you see ptrdiff_t with no pointer in sight it's not very clear unless you are familiar with C idioms (and I never remember seeing this back when I learnt C - some modern thing).
Re: Bug? 0 is less than -10
On Tuesday, 6 October 2015 at 14:46:56 UTC, tcak wrote:
Maybe I am just too stressed out to see the problem.
[code]
import std.stdio;
void main(){
size_t dec = 0;
writeln( dec, " ", (dec <= -10), " ", (dec >= 10), " ", ((dec
<= -10) || (dec >= 10)) );
}
[/code]
[output]
0 true false true
[/output]
How is it generating "true" for (dec <= -10) ? Is there a
special casting or something?
DMD 2.068.2, Ubuntu 64-bit
Lionello Lunesu posted a PR that should fix this:
https://github.com/D-Programming-Language/dmd/pull/1913
See also the discussion in the linked bug report.
Unfortunately it seems it's been forgotten since then...
Re: Bug? 0 is less than -10
On Wednesday, 7 October 2015 at 02:53:32 UTC, Steven Schveighoffer wrote: On 10/6/15 7:21 PM, Laeeth Isharc wrote: could we have ssize_t defined in phobos somewhere so your code ends up being portable ;) (It's trivial to do, obviously). ptrdiff_t -Steve It seems unnatural to use such a name when the variable has nothing to do with pointers - it doesn't contribute to the readability. Yes, it's trivial, but small things cumulatively matter. Adam tends to use int and when that gets mixed up with an auto size_t (eg via length) then his code doesn't compile on 64 bit. And if it happens with his code, you can imagine this isn't a problem that inexperienced users never encounter.
Re: Bug? 0 is less than -10
On Tuesday, 6 October 2015 at 14:46:56 UTC, tcak wrote:
Maybe I am just too stressed out to see the problem.
[code]
import std.stdio;
void main(){
size_t dec = 0;
writeln( dec, " ", (dec <= -10), " ", (dec >= 10), " ", ((dec
<= -10) || (dec >= 10)) );
}
[/code]
[output]
0 true false true
[/output]
How is it generating "true" for (dec <= -10) ? Is there a
special casting or something?
DMD 2.068.2, Ubuntu 64-bit
dec is a size_t. size_t is unsigned. -10 is cast to unsigned for
the comparison, resulting in some huge value.
Re: Bug? 0 is less than -10
On Tuesday, 6 October 2015 at 14:46:56 UTC, tcak wrote:
void main(){
size_t dec = 0;
How is it generating "true" for (dec <= -10) ? Is there a
special casting or something?
size_t is unsigned, so the -10 is cast to unsigned too for the
comparison which yields some huge number.
Comparing signed to unsigned is almost always a mistake... but
one D inherited from C.
This is a reason why I prefer to use int instead of size_t where
I can but that might require casts and truncation too.
Re: Bug? 0 is less than -10
On 10/6/15 7:21 PM, Laeeth Isharc wrote: could we have ssize_t defined in phobos somewhere so your code ends up being portable ;) (It's trivial to do, obviously). ptrdiff_t -Steve
Re: Bug? 0 is less than -10
On Tuesday, 6 October 2015 at 14:55:23 UTC, Adam D. Ruppe wrote:
On Tuesday, 6 October 2015 at 14:46:56 UTC, tcak wrote:
void main(){
size_t dec = 0;
How is it generating "true" for (dec <= -10) ? Is there a
special casting or something?
size_t is unsigned, so the -10 is cast to unsigned too for the
comparison which yields some huge number.
Comparing signed to unsigned is almost always a mistake... but
one D inherited from C.
This is a reason why I prefer to use int instead of size_t
where I can but that might require casts and truncation too.
could we have ssize_t defined in phobos somewhere so your code
ends up being portable ;) (It's trivial to do, obviously).
Re: Bug? 0 is less than -10
On Tuesday, 6 October 2015 at 14:46:56 UTC, tcak wrote:
Maybe I am just too stressed out to see the problem.
[code]
import std.stdio;
void main(){
size_t dec = 0;
writeln( dec, " ", (dec <= -10), " ", (dec >= 10), " ", ((dec
<= -10) || (dec >= 10)) );
}
[/code]
[output]
0 true false true
[/output]
How is it generating "true" for (dec <= -10) ? Is there a
special casting or something?
DMD 2.068.2, Ubuntu 64-bit
If you need to mix signed and unsigned values but want to avoid
this issue, you an use the comparison functions from
std.functional.
http://dlang.org/phobos/std_functional.html#.lessThan
