Implementing and optimizing a simple graph metric
Joseph Rushton Wakeling
joseph.wakeling at webdrake.net
Wed Sep 18 09:40:43 PDT 2013
On Wednesday, 18 September 2013 at 15:22:51 UTC, bearophile wrote:
> Joseph Rushton Wakeling:
>> I haven't yet tried alloca or other manual memory management
>> -- I felt a bit resistant to this as I'd prefer to keep the
>> code simple and readable -- but I'll give that a go too just
>> to see how it goes.
> I'd like some stack-allocated variable-length array in
> D+Phobos, as in C++14. It's also a basis to build several other
> stack-allocated data structures.
Yes, that'd be useful, although in the case of this code I think
that stack vs. heap probably isn't that important. If the data
is small enough for stack allocation, the calculation will be
>> However, my impression now is that having or not having it, or
>> any other method (e.g. enum T0, T1, etc.) makes absolutely no
>> difference, and that I might as well be simple and write 0 for
>> integral-types, 0.0 for floating-point.
> Right. And this could be right even if you want T=Rational.
Actually, on re-testing this just now, I'm returning to my
original view. I find that if you put in raw floating-point
numbers like 0.0, 1.0 etc. the resulting code can be slower in
the case where T = float. Putting to!T or using enums as you
suggest appears to make no difference.
This is a guess rather than confirmed by looking at assembly, but
I'm presuming that to!T(0) and other conversions of compile-time
constants are evaluated at compile time, so you don't in practice
carry the cost you'd normally get from using to().
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