On 9/25/16 4:19 AM, Jon Degenhardt wrote:
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!
Thanks for this work! -- Andrei
