www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - scanf vs std.stream.stdin.scanf - scanf.d.txt

reply g.wiener comcast.net writes:
I just downloaded the Linux version of D on Jan 31, 2005.

I've run a simple test comparing the performance of the C version of scanf (in
D) versus the std.stream.stdin.scanf performance.

On my Debian linux box, the D version of std.stream.stdin.scanf is 10 times
slower on a file consisting of 768000 numbers than the C version.

I'm wondering why there is such a drastic difference in processing speed.

Thanks,

Gerry Wiener



extern(C)
{
int  scanf	(char *, double *);
}

int main()
{
double sum = 0;
double value;   

while (scanf("%lg", &value)>= 0)
{
sum += value;	
}

printf("sum = %g\n", sum);
return(0);
}


--------------------------------------------------------------------


import std.stream;

int main()
{
double sum = 0;
double value;   

while (std.stream.stdin.scanf("%lg", &value)>= 1)
{
sum += value;	
}

printf("sum = %g\n", sum);
return(0);
}
Feb 12 2005
parent reply "Ben Hinkle" <ben.hinkle gmail.com> writes:
Most likely you are seeing the fact that std.stream.stdin is not buffered. 
If you replace the line
while (std.stream.stdin.scanf("%lg", &value)>= 1)
with
BufferedStream bufferedin = new BufferedStream(stdin);
while (bufferedin.scanf("%lg", &value)>= 1)
then on WinXP where I tested it goes from about 7 times slower than the C 
version to 2 times faster than the C version.

<g.wiener comcast.net> wrote in message 
news:culubm$2mbl$1 digitaldaemon.com...
I just downloaded the Linux version of D on Jan 31, 2005.

 I've run a simple test comparing the performance of the C version of scanf 
 (in
 D) versus the std.stream.stdin.scanf performance.

 On my Debian linux box, the D version of std.stream.stdin.scanf is 10 
 times
 slower on a file consisting of 768000 numbers than the C version.

 I'm wondering why there is such a drastic difference in processing speed.

 Thanks,

 Gerry Wiener



 extern(C)
 {
 int  scanf (char *, double *);
 }

 int main()
 {
 double sum = 0;
 double value;

 while (scanf("%lg", &value)>= 0)
 {
 sum += value;
 }

 printf("sum = %g\n", sum);
 return(0);
 }


 --------------------------------------------------------------------


 import std.stream;

 int main()
 {
 double sum = 0;
 double value;

 while (std.stream.stdin.scanf("%lg", &value)>= 1)
 {
 sum += value;
 }

 printf("sum = %g\n", sum);
 return(0);
 }


 

Feb 12 2005
parent reply Gerry Wiener <Gerry_member pathlink.com> writes:
Thanks Ben -- that's it! Now I'm seeing D outperform gcc by about 10% on this
example.

--Gerry

In article <cum1jh$2pas$1 digitaldaemon.com>, Ben Hinkle says...
Most likely you are seeing the fact that std.stream.stdin is not buffered. 
If you replace the line
while (std.stream.stdin.scanf("%lg", &value)>= 1)
with
BufferedStream bufferedin = new BufferedStream(stdin);
while (bufferedin.scanf("%lg", &value)>= 1)
then on WinXP where I tested it goes from about 7 times slower than the C 
version to 2 times faster than the C version.

<g.wiener comcast.net> wrote in message 
news:culubm$2mbl$1 digitaldaemon.com...
I just downloaded the Linux version of D on Jan 31, 2005.

 I've run a simple test comparing the performance of the C version of scanf 
 (in
 D) versus the std.stream.stdin.scanf performance.

 On my Debian linux box, the D version of std.stream.stdin.scanf is 10 
 times
 slower on a file consisting of 768000 numbers than the C version.

 I'm wondering why there is such a drastic difference in processing speed.

 Thanks,

 Gerry Wiener



 extern(C)
 {
 int  scanf (char *, double *);
 }

 int main()
 {
 double sum = 0;
 double value;

 while (scanf("%lg", &value)>= 0)
 {
 sum += value;
 }

 printf("sum = %g\n", sum);
 return(0);
 }


 --------------------------------------------------------------------


 import std.stream;

 int main()
 {
 double sum = 0;
 double value;

 while (std.stream.stdin.scanf("%lg", &value)>= 1)
 {
 sum += value;
 }

 printf("sum = %g\n", sum);
 return(0);
 }


 


Feb 12 2005
parent "Ben Hinkle" <ben.hinkle gmail.com> writes:
"Gerry Wiener" <Gerry_member pathlink.com> wrote in message 
news:cumc3n$6u$1 digitaldaemon.com...
 Thanks Ben -- that's it! Now I'm seeing D outperform gcc by about 10% on 
 this
 example.

 --Gerry

It would be interesting to find out what the buffer size is for gcc. Maybe it really is worth making the stdio stream buffered by default. The lines in question are way at the bottom of std.stream it says things like stdin = new File(0, FileMode.In); and all we would need to do if we decide to make them buffered is stdin = new BufferedFile(0, FileMode.In); -Ben
Feb 12 2005