[TV]

In the context (but limited to) of [apache server with tcl cgi scripts running on safe user] I've done some small tests to compare signal processing loops in tcl with C, primarily speed-wise. Of course a loop is not the same as computations, and a compilation not the same as a free run-time interpreted program such as tcl can handle, and moreover tcl/tk scripts can very well drive a C compiler to make it's use more comfortable.

I can get pretty fast not-so-big C compiles running on moderately fast machines running Linux, expecially when using a Ram disk for temporary data storage:

  export TMP=/dev/shm
  export TEMP=/dev/shm

In a bash shell.

The first Tcl test program is very short:

 ~/Math [1008] $ cat > test1.tcl
 for {set i 0} {$i < 100000} {incr i} {set y [expr 10*$i] }
 ~/Math [1009] $ time tclsh test1.tcl 
 real    0m1.021s
 user    0m0.962s
 sys     0m0.006s

The equivalent in C, but with a 1e3 times longer loop:

 ~/Math [1053] $ cat test1.c
  #include<stdio.h>
 
 main()
 {
    int i;
    long int y = 0;
    for (i=0; i<100000000; i++) y+=10*i;
    printf("%ld\n",y);
 }
 
 ~/Math [1054] $ gcc -o test1 test1.c
 ~/Math [1055] $ time ./test1
 49999999500000000
 real    0m0.505s
 user    0m0.379s
 sys     0m0.001s
 
Ok, 2000 times faster loop, and this length is the static compiled crossover point as a result of the compilatation taking a part of 1 second.

Now with processing:

 ~/Math [1056] $ cat test2.tcl 
 set y 0;
 for {set i 0} {$i < 100000} {incr i} {set y [expr $y +  sin($i/10000)]}
 puts $y
 ~/Math [1057] $ time tclsh test2.tcl 
 19552.09482105695
 real    0m3.997s
 user    0m3.173s
 sys     0m0.007s

In C:

 ~/Math [1058] $ cat test2.c
 
 #include<stdio.h>
 #include<math.h>
 
 main()
 {
    int i;
    double y = 0;
    for (i=0; i<100000000; i++) y+=sin(i/10000);
    printf("%lf\n",y);
 }
 
 ~/Math [1059] $ gcc -O -o test2 test2.c -lm
 ~/Math [1060] $ time ./test2
 19395.054107
 
 real    0m10.094s
 user    0m7.659s
 sys     0m0.020s
 ~/Math [1061] $ time ./test2
 19395.054107
 
 real    0m8.081s
 user    0m8.030s
 sys     0m0.003s
 ~/Math [1062] $ time ./test2
 19395.054107 
 
 real    0m7.949s
 user    0m7.895s
 sys     0m0.009s
 ~/Math [1063] $ 

Of course the overhead of the loop starts to count less, and probably tcl used the same C library sin() call, so not 2000 but 500 times faster. (the last two time-s I switched of the TV running on the same machine).

Someone want to compare multicore or VHDL ?

Oh, another good practicum question: why is the result from the C and the tcl code ''exactly'' different?!

----
[TV] ''Sept 3 ´08'' I add a page about a similar subject [List computations in a FPGA, driven by Tcl] which is interesting to compare speeds.

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!!!!!!
%| [Category Performance]|[Category Testing] |%
!!!!!!