Its all about using the right language for the job.

@res = p_process('    aaaa    bbbbccccccccbbb aaaaabbbbbcddddddddddddd
+ddddddd');

print Dumper(@res);

use Inline C => <<'END_OF_C_CODE';

void p_process(char *s) {
    char prev = 'Q';
    long count = 0;
    long pos = 0;
    long i=0;
    AV *array;
    
    Inline_Stack_Vars;
    Inline_Stack_Reset;


    while(*s != 0) {
        if (count==0) {
            pos = i;   
            prev = *s;
            count = 1;
        } else if (prev == *s) {
            count++;            
        } else {
            array = newAV();
                            
            av_push(array,newSVpvn(&prev,1));
            av_push(array,newSViv(pos));     
            av_push(array,newSViv(count));
            Inline_Stack_Push(newRV_inc(array));
            pos=i;                              
            prev = *s;
            count=1;  
        }
         
        i++;
        s++;
    }       
    Inline_Stack_Done;
}
 
END_OF_C_CODE
[download]

(Note, if you have a very long string, you should look at shifting things into a top-level array instead of onto the stack directly, since the stack might run out of room)

This one doesn't handle char 0, since that is the C string termination character. A fairly trivial modification to using the SV as it comes in would fix that however.

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