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digitalmars.D.learn - why my tail implementation is much more slower than coreutil ?

reply bioinfornatics <bioinfornatics fedoraproject.org> writes:
my tail implementation do not provides all features exposed by
coreutil.tail. Just able to read a file no stdout or piping and my D
implementation is slower than coreutil.tail.


---- coreutil tail -----
$ time tail tail.d
                }
                else currentPosition--;
            }
            else
                currentPosition--;
        }
        if( currentPosition !=3D f.length ) writeln( cast(string)
f[currentPosition .. f.length] );
    }
    exit(0);
}

real	0m0.002s
user	0m0.001s
sys	0m0.001s
---- mine tail implementation -----
$ time ./tail tail.d
                else currentPosition--;
            }
            else
                currentPosition--;
        }
        if( currentPosition !=3D f.length ) writeln( cast(string)
f[currentPosition .. f.length] );
    }
    exit(0);
}


real	0m0.011s
user	0m0.004s
sys	0m0.007s

----- Code tail.d ----
import std.mmfile;
import std.getopt;
import std.stdio    : writeln, writefln;
import std.ascii    : isWhite;
import std.c.stdlib : atexit, exit;
import core.runtime : Runtime;

string programName      =3D "" ;
enum   programVersion   =3D "0.0.1";

extern (C) void terminateRuntime (){
    Runtime.terminate();
}

bool isNewline(dchar c)  safe pure nothrow {
    return ( c =3D=3D 0x0A || c =3D=3D 0x0D )? isWhite( c ) : false;
}


void main( string[] args ){
    void usage(){
        writefln( "%s [OPTION]... [FILE]...", programName );
        writefln( "%s is under GPL v3+", programName );
        writefln( "version: %s", programVersion );
        writeln("    -n, --lines=3DK   output the last K lines, instead of
the last 10; or use -n +K to output lines starting with the Kth" );
        writeln("    -h, --help      display this help and exit" );
        writeln("    --version       output version information and
exit" );
        exit(0);
    }

    void printVersion(){
        writefln( "%s is under GPL v3+", programName );
        exit(0);
    }

    programName                 =3D args[0];
    size_t lineNumber           =3D 10;
    size_t currentLineNumber    =3D 0;
    ulong  currentPosition      =3D 0;
    bool   isRunning            =3D true;

    atexit(&terminateRuntime);

    if ( args.length =3D=3D 1 ) usage();

    getopt(
        args,
        "lines|n", &lineNumber,
        "help|h" , &usage,
        "version", &printVersion
    );

    foreach( filename; args[1..args.length] ){
        MmFile  f       =3D new MmFile( filename );
        if ( f.length > 0 )
            currentPosition =3D f.length - 1 ;
        else
            isRunning =3D false;

        while( isRunning ){
            if ( currentLineNumber >=3D lineNumber || currentPosition - 1
< 0)
                isRunning =3D false;
            else if( isNewline( cast(dchar) f[currentPosition] ) ){
                currentLineNumber++;
                if(currentLineNumber >=3D lineNumber){
                    isRunning =3D false;
                    currentPosition++; // do not take tne newline to
output
                }
                else currentPosition--;
            }
            else
                currentPosition--;
        }
        if( currentPosition !=3D f.length ) writeln( cast(string)
f[currentPosition .. f.length] );
    }
    exit(0);
}
Nov 04 2012
next sibling parent Timon Gehr <timon.gehr gmx.ch> writes:
How long does the hello world program take? I guess it is just that the 
D program has a slightly higher startup cost than the C program.
Nov 04 2012
prev sibling next sibling parent bioinfornatics <bioinfornatics fedoraproject.org> writes:
Le dimanche 04 novembre 2012 =C3=A0 17:36 +0100, bioinfornatics a =C3=A9cri=
t :
 my tail implementation do not provides all features exposed by
 coreutil.tail. Just able to read a file no stdout or piping and my D
 implementation is slower than coreutil.tail.

convenience way to look the code http://pastebin.geany.org/wWUYu/ Maybe Mmfile is useless since i read once time the file and i never come back to a any position in file, then map the file cost too?
Nov 04 2012
prev sibling parent Marco Leise <Marco.Leise gmx.de> writes:
tail from coreutils was compiled using the GCC. Use the same
compiler backend (GDC). Any difference that still remains is
from runtime initialization/termination, the overhead of using
a wrapper class around the C routines (for the memory mapping
or printing to terminal) and possibly a faster scan routine for
line endings in the Linux tool. Implementations using SSE to
scan for \n in a block of 16 bytes are possible.

-- 
Marco
Nov 04 2012