User:Ssvb

D language for programming competitions

Not everything is perfect:

• Hash tables are vulnerable: https://issues.dlang.org/show_bug.cgi?id=7179 and https://codeforces.com/contest/1676/submission/156707849
• Arithmetic overflows detection is not the best
• 128-bit data type is missing
• std.bigint is slow (not using GMP as a backend)
• std.random is slow: https://codeforces.com/blog/entry/99292#comment-881097

GDC tips and tricks

GDC 11+ requires "-flto" or "-fno-weak-templates" option to avoid a major performance regression: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102765

Shared library linking workaround to run phobos unit tests: https://bugzilla.gdcproject.org/show_bug.cgi?id=199

Demangle symbols: https://dlang.org/phobos/std_demangle.html

Mingw build and test instructions: TODO

Arithmetic overflows

TODO: create a new DIP? https://forum.dlang.org/post/rclilxjpnjvexggncfhd@forum.dlang.org

TODO: Atomic operations and arithmetic overflows?

TODO: Unsigned overflows?

GDC supports "-ftrapv" easter egg option for trapping signed overflows.

Relevant links:

• https://dlang.org/phobos/core_checkedint.html
• https://forum.dlang.org/post/s3dm64$2f2i$1@digitalmars.com
• https://news.ycombinator.com/item?id=24575780
• https://gcc.gnu.org/legacy-ml/gcc/2014-07/msg00251.html
• https://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html

GCC history of -fno-strict-aliasing and -fwrapv:

• https://www.mail-archive.com/redhat-list@redhat.com/msg18009.html
• https://lists.gnu.org/archive/html/autoconf-patches/2006-12/msg00091.html
• https://lists.gnu.org/archive/html/bug-gnulib/2006-12/msg00094.html
• https://gcc.gnu.org/legacy-ml/gcc/2008-02/msg00732.html

Associative arrays and hash collisions

https://forum.dlang.org/post/navsnrjweslsqeaawsev@forum.dlang.org

A hacked solution on codeforces (integers): https://codeforces.com/contest/1676/submission/156707849 A hacked solution on codeforces (strings): https://codeforces.com/contest/1703/submission/163949653

Relevant links:

• https://en.wikipedia.org/wiki/Collision_attack#Hash_flooding
• https://en.wikipedia.org/wiki/SipHash
• https://github.com/google/highwayhash ("Defending against hash flooding" section)
• https://github.com/google/highwayhash/issues/28
• https://github.com/tkaitchuck/aHash/blob/master/compare/readme.md
• https://www.josephkirwin.com/2018/04/07/z3-hash-inversions
• http://emboss.github.io/blog/2012/12/14/breaking-murmur-hash-flooding-dos-reloaded/

Long term support version of D language

The 2.076 frontend from GDC 9/10/11 can be essentially treated as a D language "edition 2017". This old frontend can be also added to GDC 12 by essentially reverting the frontend upgrade commits, but preferably both frontends should be supported in a single compiler release and selected via '-std=' option.

• https://forum.dlang.org/post/sysghhzfdyojcbosxlkm@forum.dlang.org

Victims of compatibility breaking changes:

• https://forum.dlang.org/post/t7lqbe$1cmn$1@digitalmars.com
• https://forum.dlang.org/post/bwjrwzpqmidhcgdybnom@forum.dlang.org