Most performant way of converting int to string

[rumbu via Digitalmars-d-learn]

On Tuesday, 22 December 2015 at 20:52:07 UTC, rumbu wrote:
> On Tuesday, 22 December 2015 at 19:45:46 UTC, Daniel Kozák 
> wrote:
>> V Tue, 22 Dec 2015 18:11:24 +0000
>> rumbu via Digitalmars-d-learn 
>> <digitalmars-d-learn at puremagic.com>
>> napsáno:
>>
>>> On Tuesday, 22 December 2015 at 17:15:27 UTC, Andrew Chapman 
>>> wrote:
>>> > Sorry if this is a silly question but is the to! method 
>>> > from the conv library the most efficient way of converting 
>>> > an integer value to a string?
>>> >
>>> > e.g.
>>> > string s = to!string(100);
>>> >
>>> > I'm seeing a pretty dramatic slow down in my code when I 
>>> > use a conversion like this (when looped over 10 million 
>>> > iterations for benchmarking).
>>> >
>>> > Cheers!
>>> 
>>> Converting numbers to string involves the most expensive 
>>> known two operations : division and modulus by 10.
>>
>> No, IIRC few months or maybe years I have optimize this so it 
>> does not use division and modulus
>
> It's using division and modulus, as expected:
>
> https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L5529
>
> If the compiler is smart enough, maybe it will replace this by 
> well known multiplication trick.

Tested it, I was right:

No optimizations: two divisions, one for the modulus and one for 
the division itself
Optimized: multiplication by 0xCCCCCCCD trick.

http://imgur.com/a/lHeHe