Re: C++ Interop
On Saturday, 6 January 2018 at 11:20:01 UTC, Seb wrote: On Saturday, 6 January 2018 at 11:17:56 UTC, Seb wrote: On Friday, 5 January 2018 at 13:02:12 UTC, qznc wrote: I'm exploring [0] C++ interop after watching Walter's presentation [1]. [...] I know about this: https://github.com/Remedy-Entertainment/binderoo https://github.com/dlang/druntime/pull/1802 And: https://github.com/dlang/druntime/pull/1316 Also I think Ian (@ibuclaw) and @Razvan7 are currently working on a header generation tool from D sources to C++ headers. It would be great to have std::vector and std::string out of the box in D, but putting it into druntime? Druntime is supposed to be shared among all frontends, isn't it? GCC and Clang probably do not have equivalent vector/string classes that the same D code can be used.
C++ Interop
I'm exploring [0] C++ interop after watching Walter's presentation [1]. I hit a block with classes as template parameters. This means vector works, but vector does not. D seems to map vector!Foo to vector. Likewise shared_ptr is a problem. Any way to fix that on the D side? The ugly workaround is to adapt the C++ code. I understand that this mapping makes sense for function calls because bar(Foo f) in D maps to bar(Foo *f) in C++. And C++ bar(Foo f) has no equivalent in D because classes are reference types. On a related note, C++ interop requires to redeclare or even reimplement C++ code. Has anybody started a libcpp-in-d project? I'm looking for basics like vector and string. [0] https://github.com/qznc/d-cpptest [1] https://youtu.be/IkwaV6k6BmM
Re: Use of "T"
On Wednesday, 12 April 2017 at 13:17:42 UTC, solidstate1991 wrote: How can I make use of T? I've seen it being used many times for this application. What "T"? This letter is often used as a generic template parameter. Are you talking about templates? Maybe you can give some examples of the "many times" you have seen it used?
Dub and bindings
Are there any general tips or best practices for bindings in dub packages? For example, I love the d2sqlite3 package. It just works out of the box. No linker configuration or anything. However, that is probably a testament to sqlite's lack of dependencies. That cannot work for libraries, which rely on other libraries. Should the C code be included in the Github repo? Are submodules fine? Should the C build be invoked by dub via "preBuildCommands"? What about system libraries? Can that be made cross-platform? Should lflags be specified in the dub config or should they be passed via environment variable? There should be a general guide for this. Maybe there already is one?
Re: About spinlock implementation
On Thursday, 1 September 2016 at 10:30:12 UTC, Guillaume Piolat wrote: On Thursday, 1 September 2016 at 07:46:04 UTC, qznc wrote: I find the documentation on MemoryOrder lacking about the semantics of rel. :( [0] https://dlang.org/library/core/atomic/memory_order.html What helped me was to read std::memory_order documentation http://en.cppreference.com/w/cpp/atomic/memory_order Yes, but how do they map? Is D's rel = relaxed or release or acq_rel? Also, reading C++ documentation should not be required of course. ;)
Re: About spinlock implementation
On Thursday, 1 September 2016 at 06:44:13 UTC, mogu wrote:
I found an implementation of spinlock in concurrency.d.
```
static shared struct SpinLock
{
void lock() { while (!cas(&locked, false, true)) {
Thread.yield(); } }
void unlock() { atomicStore!(MemoryOrder.rel)(locked,
false); }
bool locked;
}
```
Why atomicStore use MemoryOrder.rel instead of MemoryOrder.raw?
I'm not sure I understand rel [0], but raw is too weak. Raw means
no sequencing barrier, so
local_var = protected_value;
spinlock.unlock();
could be transformed (by compiler or CPU) to
spinlock.unlock();
local_var = protected_value;
This effectively makes the access to the protected value
unprotected and nullifies the effect of the spinlock.
I find the documentation on MemoryOrder lacking about the
semantics of rel. :(
[0] https://dlang.org/library/core/atomic/memory_order.html
Re: Implementing a cache
On Saturday, 2 July 2016 at 12:21:14 UTC, Lodovico Giaretta wrote: On Saturday, 2 July 2016 at 12:10:28 UTC, qznc wrote: Alternatively, any better idea to implement the cache? I guess there is no off-the-shelf/dub solution. For now, I settled for a sorted array of cache entries plus an AA to map urls to indices into this array. https://github.com/qznc/d-github/commit/46c013c650d2cf34911ad3e10308ee6a0b5e3690#diff-24abb1e4df591f2d28947bbde1a09220R79
Implementing a cache
I want to implement some caching for HTTP GET requests. Basically a map of URL to content. A cache needs some additional meta data (size, age, etc). There seem to be two basic data structures available: Associative array (AA) or red black tree (RBT). With AA cache eviction is inefficient. It requires to sort the keys of the AA with respect to a field in the value. Stack overflow says "use RBT instead" [0]. With RBT retrieving something is inefficient. To get an entry, we need to create an fake entry with the key and get a range of entries 'equal' to the fake one? Or can I exploit some "find on sorted range" algorithm somewhere? Alternatively, any better idea to implement the cache? I guess there is no off-the-shelf/dub solution. [0] https://stackoverflow.com/questions/10060625/how-to-sort-associative-arrays
Re: String compare in words?
On Sunday, 29 May 2016 at 17:42:48 UTC, Era Scarecrow wrote: Worse I'm not sure if the code generation already does that and possibly does a better job than what we could do by hand... Not with dmd v2.071.0 or ldc 0.17.1. At least not in all the variations I tried to trick them with, like copying into fixed-size array. Well, they did insert a memcmp and libc is probably optimized like that, but they copied data first, which is unnecessary.
Re: String compare in words?
On Sunday, 29 May 2016 at 18:15:16 UTC, qznc wrote:
On Sunday, 29 May 2016 at 17:38:17 UTC, Jonathan M Davis wrote:
And if you're not simply comparing for equality, what are you
looking to figure out? Without more information about what
you're trying to do, it's kind of hard to help you.
If I write the comparison naively, the assembly clearly shows a
"movzbl" [0]. It loads a single byte! The other single byte
load is encoded in the address mode of "cmp". Implementation:
bool stringcmp(string x, string y) {
foreach(i; 0..x.length) {
if (x[i] != y[i]) // byte compare
return false;
}
return true;
}
It makes no sense to load single bytes here. Since we only want
to check for equality, we could load two full words and compare
four or eight bytes in one go.
Ok, to answer my own question, this looks good:
bool string_cmp_opt(immutable(ubyte)[] x, immutable(ubyte)[] y) {
pragma(inline, false);
if (x.length != y.length) return false;
int i=0;
// word-wise compare is faster than byte-wise
if (x.length > size_t.sizeof)
for (; i < x.length - size_t.sizeof; i+=size_t.sizeof) {
size_t* xw = cast(size_t*) &x[i];
size_t* yw = cast(size_t*) &x[i];
if (*xw != *yw) return false;
}
// last sub-word part
for (; i < x.length; i+=1) {
if (x[i] != y[i]) // byte compare
return false;
}
return true;
}
Any comments or recommendations?
Re: String compare in words?
On Sunday, 29 May 2016 at 17:38:17 UTC, Jonathan M Davis wrote:
And if you're not simply comparing for equality, what are you
looking to figure out? Without more information about what
you're trying to do, it's kind of hard to help you.
If I write the comparison naively, the assembly clearly shows a
"movzbl" [0]. It loads a single byte! The other single byte load
is encoded in the address mode of "cmp". Implementation:
bool stringcmp(string x, string y) {
foreach(i; 0..x.length) {
if (x[i] != y[i]) // byte compare
return false;
}
return true;
}
It makes no sense to load single bytes here. Since we only want
to check for equality, we could load two full words and compare
four or eight bytes in one go.
This example is simplified and far-fetched. Actually, this is
about the find algorithm [1].
[0] http://goo.gl/ttybAB
[1]
http://forum.dlang.org/post/vdjraubhtoqtxeshj...@forum.dlang.org
String compare in words?
Given two string (or char[] or ubyte[]) objects, I want to compare them. The naive loop accesses the arrays byte-wise. How could I turn this into a word-wise compare for better performance? Is a cast into size_t[] ok? Some Phobos helper functions?
Re: Newbie to D, first impressions and feedback on the 5 (and more) first minutes.
On Wednesday, 25 May 2016 at 09:41:10 UTC, Russel Winder wrote: I do not really have the proper resources to host such a repository and because of this I have not built one. I know I should rather than just moan, but Debian is my main platform and that is covered. Yes, this is the core problem. There is no single person, which (a) cares enough about Fedora and (b) can fix it. Unless this champion appears, Fedora will continue to suck for newbies.
Re: Newbie to D, first impressions and feedback on the 5 (and more) first minutes.
On Tuesday, 24 May 2016 at 15:27:45 UTC, llaine wrote: As written in the description I'm really new to D, I discovered it a few weeks ago thanks to the D Conf in Berlin. After playing around for couple of days with it, I wanted to share my journey with you guys on several points. Thanks for writing this! The "First 5 Minutes" (or days) are an important aspect, which the D community tries to improve. Since active D users already forgot about their first contact with D, the only information on what to improve are newbies telling their experience.
Re: reading file byLine
On Wednesday, 2 September 2015 at 13:46:54 UTC, Namal wrote:
On Wednesday, 2 September 2015 at 13:12:39 UTC, cym13 wrote:
On Wednesday, 2 September 2015 at 13:01:31 UTC, Namal wrote:
Hello,
I want to read a file line by line and store each line in a
string. I found this example with byLine and ranges. First of
all, do I need the range lib at all to do this and if so what
is the range of the end of the file?
You don't need the range lib at all, std.range provides
advanced functions to work with ranges but ranges are a
general concept. You need std.stdio though as this is doing
file operations.
A way to do it is:
void main() {
auto f = File("myfile");
string buffer;
foreach (line ; f.byLine) {
buffer ~= line;
}
f.close();
writeln(buffer);
}
Note that by default byLine doesn't keep the line terminator.
See http://dlang.org/phobos/std_stdio.html#.File.byLine for
more informations.
Thx, cym. I have a question about a D strings though. In c++ I
would just reuse the string buffer with the "=" how can I clear
the string after i store a line in the buffer and do something
with it.
Just like in C++: buffer = line;
However, you can just use "line" instead of "buffer" then. The
byLine does buffer internally, so it overwrites "line" on the
next iteration of foreach. If you want to keep the line string,
then make a copy "line.idup".
I also tried to append a line to an array of strings but it
failed because the line is a char?
Here is how to get an array of lines:
import std.stdio;
void main() {
auto f = File("myfile");
string buffer[];
foreach (line ; f.byLine) {
buffer ~= line.idup;
}
f.close();
writeln(buffer);
}
Profiling with LDC/GDC?
Is it possible to profile with LDC/GDC? At least LDC lists it as only an "idea". http://wiki.dlang.org/LDC_project_ideas
Re: linking external libs
On Thursday, 2 July 2015 at 12:10:52 UTC, Nicholas Wilson wrote: Also is there a binding to GMP somewhere? I just hacked one together. I could need the bindings to fix the pidigits benchmark. There is this 7y old code on dsource: http://www.dsource.org/projects/bindings/browser/trunk/gmp The readme says "This is in alpha state. All functions that have been tried seem to work. (8 out of many)", so not that confident.
Packing enums
I stumbled upon this interesting programming challenge [0], which
imho should be possible to implement in D. Maybe someone here
wants to try.
Task: Given two enums with less than 256 states, pack them into
one byte and provide convenient accessor functions.
Something like this:
enum X { A, B, C };
enum Y { foo, bar, baz };
alias both = TwoEnums!(X,Y);
static assert(both.sizeof == 1);
both z;
z.X = B;
z.Y = bar;
Of course, you can generalize to "n enums packed into a minimal
number of bytes".
[0] https://news.ycombinator.com/item?id=9800231
Re: std.container.Array deep-copy?
On Friday, 10 October 2014 at 10:59:59 UTC, Sag Academy wrote: On Friday, 10 October 2014 at 10:32:17 UTC, yazd wrote: Like the following? That did not work. Array!Foo y = Array!Foo(x[]); How does it not work? It compiles successfully: http://dpaste.dzfl.pl/583d20e426a0 yeah man. You are right. Sorry. I probably messed up my test file somehow.
Re: std.container.Array deep-copy?
On Friday, 10 October 2014 at 06:27:35 UTC, yazd wrote: On Thursday, 9 October 2014 at 21:24:55 UTC, qznc wrote: On Thursday, 9 October 2014 at 21:14:46 UTC, qznc wrote: How can you deep-copy a std.container.Array instance? Ok, the deep-copy problem already got resolved on reddit: Use dup. However, the error is still open. You cannot give an Array!X argument to constructor/replace/insertBefore of Array!X instances? You will just need to slice it to provide a range. Like the following? That did not work. Array!Foo y = Array!Foo(x[]);
Re: std.container.Array deep-copy?
On Thursday, 9 October 2014 at 21:14:46 UTC, qznc wrote: How can you deep-copy a std.container.Array instance? Ok, the deep-copy problem already got resolved on reddit: Use dup. However, the error is still open. You cannot give an Array!X argument to constructor/replace/insertBefore of Array!X instances?
std.container.Array deep-copy?
How can you deep-copy a std.container.Array instance? The actual array data is heap-allocated and reference-counted. Assignment and .dup only create additional references. Using a copy constructor yields an error: Array!Foo x; Array!Foo y = Array!Foo(x); Error: template std.container.Array!(Foo).Array.__ctor cannot deduce function from argument types !()(Array!(Foo)), candidates are: /opt/compilers/dmd2/include/std/container.d(2652): std.container.Array!(Foo).Array.__ctor(U)(U[] values...) if (isImplicitlyConvertible!(U, T)) /opt/compilers/dmd2/include/std/container.d(2670): std.container.Array!(Foo).Array.__ctor(Stuff)(Stuff stuff) if (isInputRange!Stuff && isImplicitlyConvertible!(ElementType!Stuff, T) && !is(Stuff == T[])) The question came up in a reddit discussion: http://www.reddit.com/r/programming/comments/2ipdpa/floss_weekly_311_the_d_language/cl4yv8w
