RE: Lexical conversion.

RE: Lexical conversion.

[Moore, Mathew L]

> > #include <sstream>
> > 
> > string convert (const int number) {
> >      ostringstream ostr;
> >      ostr << number;
> >      return ostr.str ();
> > }
> 
> Sigh! I decided (especially as most the cases I worry about 
> are in 0-9) to 
> implement it like so.. (I unit tested it so I'm reasonable 
> confident it 
> works and its about 3 times faster in the general case than 
> using printf)


Why do you suppose there is such a great speed improvement with the code
below?  It seems to me that snprintf() should be able to optimize this task
quite effectively.  The only overhead should be the parsing of the format
string, which in this case would be very simple.

--Matt


> 
> string convert(const int value) {
>   int abs_value;
> 
>   if (value >= 0) {
>     // Optimise for single digit case...
>     if (value <= 9) {
>       return string( 1, '0'+value);
>     }
> 
>     abs_value = value;
>   } else {
>     abs_value = -value;
>   }
> 
>   char buf[100];
>   char * start = buf+100;
>   char * end = start;
> 
>   do {
>     *(--start) = '0' + abs_value % 10;
>     abs_value /= 10;
>   } while (abs_value);
>   
>   if( value < 0) {
>     *(--start) = '-';
>   }
> 
>   return string(start, end-start);
> }
> 
> 
> -- 
> 
> 
> John Carter                             Phone : (64)(3) 358 6639
> Tait Electronics                        Fax   : (64)(3) 359 4632
> PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
> New Zealand
> 
> Good Ideas:
> Ruby                 - http://www.ruby-lang-org - The best of 
> perl,python,scheme without the pain.
> Valgrind             - http://developer.kde.org/~sewardj/ - 
> memory debugger for x86-GNU/Linux
> Free your books      - http://www.bookcrossing.com
> 

Re: Lexical conversion.

[Sebastian Huber]

On Wednesday 16 October 2002 06:03, Moore, Mathew L wrote:
> > > #include <sstream>
> > >
> > > string convert (const int number) {
> > >      ostringstream ostr;
> > >      ostr << number;
> > >      return ostr.str ();
> > > }
> >
> > Sigh! I decided (especially as most the cases I worry about
> > are in 0-9) to
> > implement it like so.. (I unit tested it so I'm reasonable
> > confident it
> > works and its about 3 times faster in the general case than
> > using printf)
>
> Why do you suppose there is such a great speed improvement with the code
> below?  It seems to me that snprintf() should be able to optimize this task
> quite effectively.  The only overhead should be the parsing of the format
> string, which in this case would be very simple.
>

If you can use <sstream> you should prefer it. Stringstreams are likely the 
most general and efficient way to do such conversions with C/C++. If you know 
more about the input, you can optimize of course.

Ciao
	Sebastian

Lexical conversion.

[John Carter]

What is the fastest way under gcc-3.* to convert from an int to a string?

ie. Equivalent to this yucky bit of code...

string convert( int number)
{  
  char line[80];
  sprintf( line, "%ld", number);
  return string(line);
}  

-- 


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Good Ideas:
Ruby                 - http://www.ruby-lang-org - The best of perl,python,scheme without the pain.
Valgrind             - http://developer.kde.org/~sewardj/ - memory debugger for x86-GNU/Linux
Free your books      - http://www.bookcrossing.com

Re: Lexical conversion.

[Claudio Bley]

>>>>> "John" == John Carter <john.carter@tait.co.nz> writes:

    John> What is the fastest way under gcc-3.* to convert from an int
    John> to a string?  ie. Equivalent to this yucky bit of code...

We are talking about C++, right? I don't know how fast it is (or what
your constrains are), but I would use something like that:

#include <sstream>

string convert (const int number) {
     ostringstream ostr;
     ostr << number;
     return ostr.str ();
}

-- 
Claudio Bley                                 ASCII ribbon campaign (")
Debian GNU/Linux advocate                     - against HTML email  X 
http://www.cs.uni-magdeburg.de/~bley/                     & vCards / \

Re: Lexical conversion.

[John Carter]

On Tue, 15 Oct 2002, Claudio Bley wrote:
> >>>>> "John" == John Carter <john.carter@tait.co.nz> writes:
> 
>     John> What is the fastest way under gcc-3.* to convert from an int
>     John> to a string?  ie. Equivalent to this yucky bit of code...
> 
> We are talking about C++, right? I don't know how fast it is (or what
> your constrains are), but I would use something like that:
> 
> #include <sstream>
> 
> string convert (const int number) {
>      ostringstream ostr;
>      ostr << number;
>      return ostr.str ();
> }

Sigh! I decided (especially as most the cases I worry about are in 0-9) to 
implement it like so.. (I unit tested it so I'm reasonable confident it 
works and its about 3 times faster in the general case than using printf)

string convert(const int value) {
  int abs_value;

  if (value >= 0) {
    // Optimise for single digit case...
    if (value <= 9) {
      return string( 1, '0'+value);
    }

    abs_value = value;
  } else {
    abs_value = -value;
  }

  char buf[100];
  char * start = buf+100;
  char * end = start;

  do {
    *(--start) = '0' + abs_value % 10;
    abs_value /= 10;
  } while (abs_value);
  
  if( value < 0) {
    *(--start) = '-';
  }

  return string(start, end-start);
}


-- 


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Good Ideas:
Ruby                 - http://www.ruby-lang-org - The best of perl,python,scheme without the pain.
Valgrind             - http://developer.kde.org/~sewardj/ - memory debugger for x86-GNU/Linux
Free your books      - http://www.bookcrossing.com