[Performance] std.conv.toInt is damn fast!

[Sean Kelly]

pragma wrote:
> Andrey Khropov wrote:
>> Burton Radons wrote:
>> 13) MS VC++ 8.0    (boost 1.33.1::lexical_cast<int>)            - 
>> 51.700 sec (Yes, it's hard to believe
>> but check yourself!)
> 
> <neo>Whoa.</neo>
> 
> You'd think that with all that templating going on it would simply 
> unroll into a *faster* routine, not something that runs *two whole 
> orders of magnitude* slower.

Not if you look at what lexical_cast does:

* Creates a new std::stringstream object.
* Sets a bunch of properties on the stringstream to ensure data is 
processed correctly.
* Passes the data to the stringstream via operator<<, which will involve 
DMA if the data as a string occupies more than 16 chars (the small 
string optimization catches smaller cases).
* Pulls the data back out again via operator>>.
* Checks the stringstream to ensure that no errors occurred and that no 
data remains in the stream, which includes processing any trailing 
whitespace, etc.
* Returns the new value.

It's clean and works well, but is hardly fast :-)


Sean