Re: BITS_PER_UNIT less than 8

[Boris Boesler <baembel at gmx dot de>]

Am 08.12.2007 um 02:49 schrieb Joseph S. Myers:

> On Fri, 7 Dec 2007, Ross Ridge wrote:
>
> > Boris Boesler writes:
> > > Ok, so what have I to do to write a back-end where all addresses are
> > > given in bits? Memory is addressed in bits, not bytes. So I set:
> > >
> > > #define BITS_PER_UNIT 1
> > > #define UNITS_PER_WORD 32
> >
> > I don't know if it's useful to define the size of a byte to be  
> > less than
> > 8-bits, even if that more accurately reflects the hardware.   
> > Standard C
> > requires that the char type both be at least 8 bits (UCHAR_MAX >=  
> > 256)
> > and the same size as a byte (sizeof(char) == 1).  You can't define  
> > any
> > types that are smaller than a char and have sizeof work correctly.

 I don't want to change sizes. It's addressing!


> In theory GCC supports CHAR_TYPE_SIZE > BITS_PER_UNIT, so sizeof 
> (char) is
> still 1 (sizeof counts in units of CHAR_TYPE_SIZE not  
> BITS_PER_UNIT) but a
> char is not the hardware addressing unit.  I expect this is even more
> broken in practice than BITS_PER_UNIT > 8.

 Hm, ok. So I patched some source code, one generated file and it  
seems to work for int(eger) operations.

 But if I want to add chars GCC runs into an endless loop during  
conversion (its the functions convert and convert_to_integer). In  
convert.c ~line 526 the parameters are: inprec:32 outprec:1 mode  
bitsize:8 I'm wondering about the output precision "1". In tree.def  
it is documented that a type precision is given in bits.

Any idea?
Boris