Help optimizing code?

[user1234]

On Monday, 1 January 2018 at 15:23:19 UTC, Adam D. Ruppe wrote:
> On Monday, 1 January 2018 at 15:09:53 UTC, Lily wrote:
>> I started learning D a few days ago, coming from some very 
>> basic C++ knowledge, and I'd like some help getting a program 
>> to run faster.
>
> So a few easy things you can do:
>
> 1) use `float` instead of `real`. real sucks, it is really slow 
> and weird. Making that one switch doubled the speed on my 
> computer.

Yes I've also adviced double. Double is better if the target arch 
is X86_64 since part of the operations will be made with SSE. 
With "real" the OP was **sure** to get 100% of the maths done in 
the FPU (although for all the trigo stuff there's no choice)

>
> 2) preallocate the imageData. before the loop, 
> `imageData.reserve(width*height*3)`. Small savings on my 
> computer but an easy one.
>
> 3) make sure you use the compiler optimization options like 
> `-O` and `-inline` on dmd (or use the gdc and ldc compilers 
> both of which generally optimize better than dmd out of the 
> box).
>
>
> And if that isn't enough we can look into smaller things, but 
> these overall brought the time down to about 1/3 what it 
> started on my box.