Fastest way to zero a slice of memory

[kinke]

On Sunday, 4 March 2018 at 15:23:41 UTC, Nordlöw wrote:
> When zeroing a slice of memory (either stack or heap) such as
>
>     enum n = 100;
>     ubyte[n] chunk;
>
> should I use `memset` such as
>
>     memset(chunk.ptr, 0, n/2); // zero first half
>
> or an array assignment such as
>
>     chunk[0 .. n/2] = 0; // zero first half
>
> or are they equivalent in release mode?
>
> Further, does it depend on whether the slice length is known at 
> compile-time or not?

I'd recommend not concerning yourself with such low-level 
optimizations and let the compiler do that for you, and only jump 
in yourself if profiling/benchmarking shows that there's a 
bottleneck, and prefer nice readable code otherwise.
E.g., LDC will lower `chunk[0 .. n/2] = 0` to a memset() call if 
the length is unknown at compile-time, and otherwise replace it 
with good-looking assembly code (xor vector register and store it 
consecutively to memory): https://run.dlang.io/is/I6Fq9G (click 
on ASM and check the assembly for the two functions).