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in reply to Displaying/buffering huge text files

8 million bytes? Surely on modern computers that isn't a lot, is it? It may be a lot on small embedded systems, but I doubt you have a need to interactively edit files hundreds of Mb large. And 8 bytes for each offset? You expect files that large? Your file has to exceed 64 Pb before it needs 8 byte offsets. (1 byte offset: up to 256 bytes in a file; 2 byte offset: 64k; 3 byte offset: 16 Mb; 4 byte offset: 4 Gb; 5 byte offset: 1 Tb; 6 byte offset: 256 Tb; 7 byte offset: 64 Pb; 8 byte offset: 16 Eb)

Anyway, if storing all the offsets in an index makes the index too large, why not store the offset of every 100th line? That makes your index 99% smaller. You do have to read up to 100 lines if your user jumps to a certain line, but unless you're writing a line editor, you want to read multiple lines on jumps anyway.

  • Comment on Re: Displaying/buffering huge text files

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Re^2: Displaying/buffering huge text files
by BrowserUk (Pope) on Dec 23, 2011 at 03:56 UTC
    And 8 bytes for each offset? ... 5 byte offset: 1 Tb;

    I, for one, would like to see your code for building an 5-byte index?


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    The start of some sanity?

      I, for one, would like to see your code for building an 5-byte index?
      Storing a million 5-byte integers using 5 million bytes for data, and 44 bytes additional overhead:
      my $buffer = ""; my $BYTES = 5; my $BITS_IN_BYTE = 8; my $FULL_BYTE = (1 << $BITS_IN_BYTE) - 1; sub store { my ($pos, $value) = @_; for (0 .. $BYTES - 1) { vec($buffer, $pos * $BYTES + $_, $BITS_IN_BYTE) = ($value >> ($BITS_IN_BYTE * ($BYTES - 1 - $_))) & $FULL_BYT +E; } } sub fetch { my ($pos) = @_; my $sum = 0; for (0 .. $BYTES - 1) { $sum <<= $BITS_IN_BYTE; $sum += vec($buffer, $pos * $BYTES + $_, $BITS_IN_BYTE); } $sum; } # # Testing # my $TEST_SIZE = 1_000_000; my @offsets = map {int rand 1 << ($BYTES * $BITS_IN_BYTE)} 1 .. $TEST_ +SIZE; for (my $i = 0; $i < @offsets; $i++) { store $i, $offsets[$i]; } for (my $i = 0; $i < @offsets; $i++) { my $val = fetch $i; die unless $val == $offsets[$i]; } use Devel::Size 'size'; use 5.010; say "Index size: ", size $buffer; __END__ Index size: 5000044