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portable numerical limits?


[ This really probably belongs in comp.lang.c, but what the
  hell, I need it for Guile :-]

What is the portable C trick to generate, say, the largest
representable value of type `short'?

I vaguely recall some bit-twiddling tricks, but don't want
to trust my memory on this.

If we assume 2's complement and 8-bit bytes (the latter is pretty
safe, I suppose), then the following should do
the trick:

short max_short = ~(short)((short)1 << (sizeof(short) * 8 - 1));

The question is, how portable (specifically in the Guile context)
is the assumption that signed integers are always 2's complement?

thanks,
mike.