Wednesday, 13 June 2012

Undocumented feature - interrupt - part four

Continuing from part three where we looked at "2" and "3"...

4 - Unknown

I haven't found any indication of what functionality this might be, but it does behave differently to "1", which was also unknown.  In this case it always returns a $status of 0 and $result is a blank string.  I tried folders, subfolders, filenames and a blank string, with no difference in behaviour.  I'm giving up, for now.

5 - Working directory

As discussed in part one, using numeric code "5" returns the working directory...

  working = $result

The alternative is to use $ldir...

  working = $ldir()

The alternative is more maintainable, safer and also performs better.

6 - Concatenate file path

This takes the file path which is currently in $result and then concatenates the path you pass in, automatically adding the folder delimiters where necessary.  Here's some example code...

  filepath = "C:\temp"
  $result filepath
  filepath = $result

This will then populate $result with "C:\temp\test\".  As you can see, I had excluded the delimiter from the end of both the original $result value and the value I passed it, but the interrupt command fixed that.  Again, this is another string manipulation example, I came up with something like this...

  filepath = "C:\temp" 
  if ( $scan(filepath,"/") < 1 ) ;calculate delimiter
    del = "\"
    del = "/"
  pos = $length(filepath)
  if ( filepath[pos] != del ) ;check filepath ends with delimiter
    filepath = "%%filepath%%del%%%"
  filepath = "%%filepath%%%test%%del%%%" ;concatenate filepath

As you can see, this isn't very concise, primarily because I'm accounting for Windows and Unix environments again, meaning that I have to first calculate the "del" local variable.  You could of course use $concat instead of using substitution, like I have.

I tested these two methods over 2,000,000 iterations with the following results...

  • interrupt = 00:06.67, 00:06.75, 00:06.72 (almost 7 seconds)
  • alternative = 00:12.02, 00:12.00, 00:12.04 (about 12 seconds)
  • without $scan = 00:09.04, 00:09.78, 00:09.74 (almost 10 seconds)

I added a third option which was the alternative but with a hardcoded delimiter instead of calculating it, so the performance can be improved by having a global register that holds this.  Still, in this case the interrupt command is better for performance and is less lines of code.  

Summary: Numeric code "4" remains unknown for now, "5" has been replaced by a better alternative and "6" seems to still be useful, although I think I'd still opt for string manipulation which I know that I can control over an undocumented feature.

No comments:

Post a Comment