Re: [RFA/mips] Fix crash trying to print long double float

[Andrew Cagney <cagney@gnu.org>]

> How's this?
> 
> 2004-08-08  Joel Brobecker  <brobecker@gnat.com>
> 
>         * mips-tdep.c (mips_gdbarch_init): Set size of long double
>         to 128 bits for N32 and N64 ABIs.
>         * mips-irix-tdep.c: Include "floatformat.h".
>         (mips_irix_floatformat_always_valid): New function.
>         (floatformat_mips_irix_long_double_big): New constant.
>         (mips_irix_init_abi): Set the long double floatformat.
> 
> Tested on mips-irix. OK to apply?

Yes, with these tweaks, commit:

>        set_gdbarch_long_long_bit (gdbarch, 64);
> +      set_gdbarch_long_double_bit (gdbarch, 128);

-- Set the long_double_format here (dito for other place), perhaphs 
conditional on info.byte_order == BFD_ENDIAN_BIG.

The ..._bit and ..._format methods should really be combined into a 
single object.  I think that should wait until GDB is written in an OO 
lanugage.  However, in the mean time we can group them together.

>        break;

-- Move this to mips-tdep and, after some thought, call it n32n64.

> +static int
> +mips_irix_floatformat_always_valid (const struct floatformat *fmt,
> +                                    const char *from)
> +{
> +  return 1;
> +}
> +
> +/* FIXME: brobecker/2004-08-08: Long Double values are 128 bit long.
> +   They are implemented as a pair of 64bit doubles where the high
> +   part holds the result of the operation rounded to double, and
> +   the low double holds the difference between the exact result and
> +   the rounded result.  So "high" + "low" contains the result with
> +   added precision.  Unfortunately, the floatformat structure used
> +   by GDB is not powerful enough to describe this format.  As a temporary
> +   measure, we define a 128bit floatformat that only uses the high part.
> +   We lose a bit of precision but that's probably the best we can do
> +   for now with the current infrastructure.  */
> +
> +static const struct floatformat floatformat_mips_irix_long_double_big =
> +{
> +  floatformat_big, 128, 0, 1, 11, 1023, 2047, 12, 52,
> +  floatformat_intbit_no,
> +  "floatformat_ieee_double_big",
> +  mips_irix_floatformat_always_valid
> +};

IRIX effectively defines the n32/n64 ABIs.  If the other systems differ, 
they can override both the _bit and _format in their local -tdep file.

Andrew