On Saturday, 24 September 2016 at 18:22:51 UTC, Andrei
Alexandrescu wrote:
Got curious so I tried to patch my ldc installation (0.17.1
(DMD v2.068.2, LLVM 3.8.0)), but sadly that didn't work out
because sorting.d uses the new syntax in various places.
Probably the best baseline is the equivalent C++ code using the
mature implementation of nth_element, see
http://paste.ofcode.org/ieZPdchjzTXbDcG3LvsYBP (also pasted at
the end of this message). Here's what I got:
http://paste.ofcode.org/6feyBLRiJtieHdZ3bmGaUW, see also text
below.
The topN code produced with dmd is faster in virtually all
cases (has parity for -f 4, which I suspect is a degenerate
case with most elements equal, which exercises only a small
part of the algorithm). For C++ I used -O3 -DNDEBUG, any other
flags I should use?
[snip]
I added the topN pull request to a local LDC build (current LDC
master). Also built the C++ nth_element and sort program you
listed. (GCC 4.9.3, compiler line: g++-mp-4.9 -O3 -static-libgcc
-static-libstdc++ -std=c++11).
Did 7 runs for each variant on the three fields in ngram file.
Median times are below.
Median sort times (ms):
Field 2 Field 3 Field 4
DMD 351 348 326
LDC 273 261 245
C++ 281 260 246
Median topN / nth_element times (ms):
Field 2 Field 3 Field 4
LDC 21 44 57
C++ 41 60 71
Looking very good indeed!
