Re: short int and conversions

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Thu, 17 Mar 2005, Andrea wrote:

> I'm trying to port gcc 4.1 for an architecture that has the following
> memory layout BITS_PER_UNIT=32 and UNITS_PER_WORD=1.

Support for systems with bytes wider than 8 bits is somewhat bitrotten at 
present, as it seems little has been done on the c4x port lately and it is 
the only such port we currently have; various PRs indicate it simply 
doesn't work (won't build libgcc) at present.  I have however CC:ed the 
maintainer of the c4x port in case he should wish to improve the state of 
this port and the general support for such ports.

> It has support (16bit registers and operators) for 16bit signed
> atithmetic used mainly for addressing. There are also operators for 32
> bit integer and floating point support.
> I set SHORT_TYPE_SIZE=POINTER_SIZE=(BITS_PER_WORD/2).

short needs to have at least the precision of char in C.  (C99 made 
explicit various aspects of the ordering rules for type precision which 
C90 was insufficiently complete about.)

However, types narrower than char do work in the compiler - we have them 
for bit-fields.  As required by the C standard, types narrower that int 
are promoted to int in arithmetic.  Bit-field types don't have their own 
modes, but in principle you should be able to have a special type with its 
own mode narrower than char: however, you may need to implement 
optimizations which convert operations on promoted types to operations on 
narrow types for targets with such types.

-- 
Joseph S. Myers               http://www.srcf.ucam.org/~jsm28/gcc/
    jsm@polyomino.org.uk (personal mail)
    joseph@codesourcery.com (CodeSourcery mail)
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