problem with formatting large integers

["Joseph Manning" <manning@...>]

Consider this simple little snippet:

  $ lua
  Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
  > for n = 2^31-2, 2^31+2 do
  >> print( string.format( "%12i %12.0f", n, n ) )
  >> end
    2147483646   2147483646
    2147483647   2147483647
   -2147483648   2147483648
   -2147483648   2147483649
   -2147483648   2147483650

The "%i" conversion works correctly only for integers up to 2^31-1,
whereas the "%.0f" conversion works for integers all the way up to
2^53-1, the maximum integer correctly represented on my platform
( Lua 5.1.4 as distributed with Debian 6.0 on an Intel x86 machine ).

Here are some options on what to do about this situation, listed in
increasing order of my own personal preference:

1) Do nothing.  Accept this small but ugly little wart in Lua,
   whereby some supposedly behind-the-scenes detail from C's "sprintf"
   pokes its way through into Lua.

2) Deprecate the "%i" (and "%d") formats, and provide "%.0f" as the
   only means to format integers.  Although this would fix the problem,
   it could cause significant breakage of existing code; additionally,
   "%.0f" just looks uglier and clumsier than "%i".

3) Rewrite the implementation of "string.format" to be independent of
   C's "sprintf", giving complete and Lua-oriented control over all the
   format conversions.  This may be a fair amount of work and may bloat
   the size of the Lua implementation.

4) Modify the current implementation of "string.format" so that all
   "%i" (and "%d") conversions are intercepted and replaced by the
   equivalent "%.0f" conversions, before then calling C's "sprintf".
   This, imho, is the best overall approach.

Any opinions on these options?  Or alternatives?

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Joseph Manning / Computer Science / UCC Cork Ireland / manning@cs.ucc.ie
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