Undefined behaviour causing problems on AVR32

Torbjorn Granlund tg at gmplib.org
Mon Apr 13 16:11:42 CEST 2009

Bradley Smith <bradsmith at debian.org> writes:

  On Mon, 13 Apr 2009 14:02:20 +0200
  Torbjorn Granlund <tg at gmplib.org> wrote:
  > I agree this is broken in GMP.
  > I don't fully understand the GMP scanf code.
  > I find two calls to sscanffuns.c's scan through the ->scan field, both
  > from __gmp_doscan.  One call uses 3 parameters and the other uses 4
  > parameters.
  > Both the current and your suggested code assumes there are 4 parameters.
  > While your code is an improvement, it still looks undefined to me.
  > Do you agree?
  Hmm, yes I didn't spot the call that uses 3 args, I guess a simple way to
  fix that would be to change the call that uses 3 args to use 4, by just
  putting a dummy argument as the 4th. Maybe not the nicest fix, but I can't
  really see an alternative that doesn't involve rewriting large chunks of
  the code.
Unfortunately, that might not work either, since the ->scan field might
point at fscanf.  (I tried this and got crashes...)

I'll try your initial solution to see if it works in practice.


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