On Thu, 22 Apr 2010 21:32:36 +0200 tlaro...@polynum.com wrote:
> On Thu, Apr 22, 2010 at 03:08:40PM -0400, ge...@plan9.bell-labs.com wrote:
> > What type is `smallnumber'?
>
> typedef unsigned char smallnumber;
^^^^^^^^
Aha!
> translated from Pascal:
>
> small_number=0..63;
IIRC in C89 integer promotions rules changed. See 6.3.1.8
(Usual arithmetic conversions)
[Otherwise,]the integer promotions are performed on both
operands. Then the following rules are applied to the
promoted operands:
If both operands have the same type, then no
further conversion is needed.
Otherwise, if both operands have signed integer
types or both have unsigned integer types, the
operand with the type of lesser integer conversion
rank is converted to the type of the operand with
greater rank.
Otherwise, if the operand that has unsigned
integer type has rank greater or equal to the rank
of the type of the other operand, then the operand
with signed integer type is converted to the type
of the operand with unsigned integer type.
>>>> Otherwise, if the type of the operand with signed
integer type can represent all of the values of
the type of the operand with unsigned integer
type, then the operand with unsigned integer type
is converted to the type of the operand with
signed integer type.
Otherwise, both operands are converted to the
unsigned integer type corresponding to the type of
the operand with signed integer type.
Try this on both gcc and 8c (with suitable changes):
#define N(i) atoi(v[i])
int f(int x, int y, unsigned char z) { return (x + y + z) / 2; }
int main(int c, char**v) { printf("%d\n", f(N(1), N(2), N(3))); }
And see what you get.
I suspect you can safely change smallnumber to a signed char
and most likely this particular problem will go away.
