From mboxrd@z Thu Jan  1 00:00:00 1970
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
In-reply-to: Your message of "Thu, 22 Apr 2010 21:32:36 +0200."
	<20100422193236.GA2388@polynum.com>
References: <20100422175033.GA6247@polynum.com>
	<87d97130a41364706523e641fe0dd372@plan9.bell-labs.com>
	<20100422193236.GA2388@polynum.com>
From: Bakul Shah <bakul+plan9@bitblocks.com>
Date: Thu, 22 Apr 2010 13:07:40 -0700
Message-Id: <20100422200740.49F7D5B73@mail.bitblocks.com>
Subject: Re: [9fans] BUG!!! in Plan9 compiler!
Topicbox-Message-UUID: 0c558d46-ead6-11e9-9d60-3106f5b1d025

On Thu, 22 Apr 2010 21:32:36 +0200 tlaronde@polynum.com  wrote:
> On Thu, Apr 22, 2010 at 03:08:40PM -0400, geoff@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.