On 05/09/2016 11:45 PM, Patric wrote:
On Monday, 5 September 2016 at 11:20:08 UTC, rikki cattermole wrote:
On 05/09/2016 11:11 PM, Patric wrote:
I´m playing remaking D functionalities with nogc structs, and to at
least match D performance.
But in this particular case i´m unable to get near D performance. Can
someone point me out what i´m doing wrong, or if there is some magic
behind the curtains on D strings?
https://dpaste.dzfl.pl/1c981fdc71ac
Ok lots of bad assumptions in there so lets declare what they should be:
1. D supports three string types, string, wstring and dstring with the
character types of char, wchar and dchar.
Strings themselves have no special behavior in the compiler as they
are arrays.
2. Types such as char are fixed in size, no point multiplying when its
a constant 1.
3. A D string is length then pointer.
Ok, now on to implementation do not use StopWatch for benchmarking.
Use benchmark[0]. This will execute the benchmark many times which
removes one off errors.
Don't directly call malloc, it will never be free'd in this case.
``new char(length)`` would be better as it will automatically be
handled by the GC.
You'll also want to reserve a block of memory to remove allocation
from the cost as much as possible (after all you're not measuring that
are you?). Don't forget to disable the GC as well so it doesn't try to
collect during the tests.
[0] https://dlang.org/phobos/std_datetime.html#.benchmark
[1] http://dlang.org/spec/type.html
[2] http://dlang.org/spec/abi.html
[3] https://github.com/dlang/druntime/blob/master/src/object.d#L41
I´m aware of 1, and 2.
I look one million times on datetime and did´nt see the benchmark,
thanks xD
My intention is to not use gc at all, so no "new" for me.
Yes the optimal case will be reserve the memory beforehand, but i´m
benchmarking the opBinary.
So now a bit better example :)
https://dpaste.dzfl.pl/b9356f57a8c8
Daniel Kozak:
Ok, now it gets a bit weird.
On DPaste it shows:
14 ms and 343 μs - DString
3 ms and 928 μs - CustomString
And on my PC (with dub release mode) :
7 ms, 885 μs, and 9 hnsecs - DString
18 ms, 740 μs, and 8 hnsecs - CustomString
(!!!)
Be a bit careful there, when a struct is moved around its destructor
will be called. This is why I suggested you to use the GC to allocate
memory or else ouch.
So you'll find very quickly that you will be having segfaults since you
will be doing use after free.
Oh and you'll want to turn that into a slice at some point ``char[] str
= ptr[0 .. length];``.
