On Saturday, 14 April 2012 at 19:05:40 UTC, ReneSac wrote:
I have this simple binary arithmetic coder in C++ by Mahoney
and translated to D by Maffi. I added "notrow", "final" and
"pure" and "GC.disable" where it was possible, but that didn't
made much difference. Adding "const" to the Predictor.p() (as
in the C++ version) gave 3% higher performance. Here the two
versions:
http://mattmahoney.net/dc/ <-- original zip
http://pastebin.com/55x9dT9C <-- Original C++ version.
http://pastebin.com/TYT7XdwX <-- Modified D translation.
The problem is that the D version is 50% slower:
test.fpaq0 (16562521 bytes) -> test.bmp (33159254 bytes)
Lang| Comp | Binary size | Time (lower is better)
C++ (g++) - 13kb - 2.42s (100%) -O3 -s
D (DMD) - 230kb - 4.46s (184%) -O -release -inline
D (GDC) - 1322kb - 3.69s (152%) -O3 -frelease -s
The only diference I could see between the C++ and D versions
is that C++ has hints to the compiler about which functions to
inline, and I could't find anything similar in D. So I manually
inlined the encode and decode functions:
http://pastebin.com/N4nuyVMh - Manual inline
D (DMD) - 228kb - 3.70s (153%) -O -release -inline
D (GDC) - 1318kb - 3.50s (144%) -O3 -frelease -s
Still, the D version is slower. What makes this speed
diference? Is there any way to side-step this?
Note that this simple C++ version can be made more than 2 times
faster with algoritimical and io optimizations, (ab)using
templates, etc. So I'm not asking for generic speed
optimizations, but only things that may make the D code "more
equal" to the C++ code.
I wrote a version http://codepad.org/phpLP7cx based on the C++
one.
My commands used to compile:
g++46 -O3 -s fpaq0.cpp -o fpaq0cpp
dmd -O -release -inline -noboundscheck fpaq0.d
G++ 4.6, dmd 2.059.
I did 5 tests for each:
test.fpaq0 (34603008 bytes) -> test.bmp (34610367 bytes)
The C++ average result was 9.99 seconds (varying from 9.98 to
10.01)
The D average result was 12.00 seconds (varying from 11.98 to
12.01)
That means there is 16.8 percent difference in performance that
would be cleared out by usage of gdc (which I don't have around
currently).
