🚀 go-pugleaf

In article <4fstj7$2l6@solutions.solon.com>,
Rune Huseby <rune.huseby@gpi.telemax.no> wrote:
:I got a problem understanding the rules on integral promotion in 
:the C language:
:
:Consider the following function:
:
:short test(short x1, short x2);
:
:int main(void)
:{
:  short result;
:  result = test(1, 2);
:  return 0;
:}
:
:short test(short x1, short x2)
:{
:  short result;
:  result = x1 + x2;  /* Warning:  '=' : conversion from 'int '                                 
:                         to 'short ', possible loss of data */
:  return result;
:}
:
:My compiler (Microsoft Visual C++ 4.0), automagically converts 
:my short-parameters to int's, even though all variables involved 
:are short. 

The parameters for a prototyped function are not converted.  That is,
x1 and x2 remain type short int.  

When they are used in most expressions which expect an int type they
undergo integral promotion, regardless of the type of the other
operands.  

:I know that the standard says that all arguments can 
:be converted to the biggest 'type' of all the arguments, but is 
:it correct that char's and short's always are promoted to int's, 
:without regard to the other arguments in the expression?

It depends on the usage, but usually yes.  Some exceptions would be
operand of sizeof, ++, --, and simple assignment.

Even though the operands are promoted in expressions, the compiler
might not actually expand the arguments if the end results are the
same.  In the example code, the compiler is free to perform the
addition using a short accumulation register, assuming the result,
when assigned to a short, is the same as would occur with promotion
and conversion to short int.

:The reason I ask is that I am writing code that should be 
:portable from a 16-bits environment (where short and int are the 
:same size) to a 32-bits environment. (My 16-bits compiler does 
:not complain about the code).

If the code is written correctly and assumptions are not made about
the maximum values, e.g., that 1 << 16 == 0, you should be OK.

Thad