From: Mauricio Fernandez <mfp@...>
Date: 2007-01-08T10:51:34+09:00
Subject: Re: SparseFile

On Mon, Jan 08, 2007 at 09:44:33AM +0900, Erik Veenstra wrote:
> I updated the implementation [1] of SparseFile [2] and added
> some unit tests [3].
> 
> Any thoughts? Ideas? Comments? I welcome any feedback.

Instead of 
    SPARSE_BLOCKS[length] ||= "\000" * length

    unless data == SPARSE_BLOCKS[length]
      @file.pos = @pos
      @file.write(data)
    end

What about

  unless data.count("\0") == data.size
    @file.pos = @pos
    @file.write(data)
  end

? Saves some mem if you have lots of "null blocks" of different sizes (or use
huge blocks), and the loop shouldn't be much slower than a strcmpish one:

    while (s < send) {
	if (table[*s++ & 0xff]) {
	    i++;
	}
    }

But a C implementation that detects leading \0s and skips them would be best.
In Ruby it'd be
  idx = data.index(/[^\0]/)
  if idx
      @file.pos += idx
      @file.write(data[idx..-1])
  else
      @file.write(data)
  end
but the regexp matching and the aref would make it way too slow.
I'll post it tomorrow if I don't forget.

-- 
Mauricio Fernandez  -   http://eigenclass.org   -  singular Ruby