Re: __LDBL_MANT_DIG__

[Gabriel Dos Reis <gdr at cs dot tamu dot edu>]

Perry Smith <pedz@easesoftware.net> writes:

| Thanks Gaby...
| 
| To recap, my current quest is to resolve references to symbols like
| __floatdidf.  This is in a library for ppc64/soft-float.
| 
| Ian pointed me to ppc64-fp.c.  When I try to compile it, TFtype is
| undefined.  It is suppose to get defined in fp-bit.h but only if
| __LDBL_MANT_DIG__ is set to 113 or 106.  Right now, in the
| environment that I have now, ___LDBL_MANT_DIG__ is set to 53.  In the
| RS/6000, long doubles are 106.  (I'm not sure if "long double" is the
| right term to use here.)
| 
| I am compiling with -maix64.  It appears to me that some parts of gcc
| or libgcc assume that this implies long double but c-cppbuiltin.c
| appears to not make that assumption.


hmm, it looks to me that there is some communication mismatch between
the target back-end and the front-end.  From
gcc/c-cppbuiltin.c:builtin_define_float_constants:

  fmt = REAL_MODE_FORMAT (TYPE_MODE (type));
  gcc_assert (fmt->b != 10);
  gcc_assert (fmt->b != 10);

  /* The radix of the exponent representation.  */
  if (type == float_type_node)
    builtin_define_with_int_value ("__FLT_RADIX__", fmt->b);
  log10_b = log10_2 * fmt->log2_b;

  /* The number of radix digits, p, in the floating-point
  significand.  */
  sprintf (name, "__%s_MANT_DIG__", name_prefix);
  builtin_define_with_int_value (name, fmt->p);


So, for some reasons, it looks like TYPE_MODE (long_double_type_node)
does not have the information you would like it to report (106,
instead of 53).

do I understand correctly that -maix64 is supposed to change the
layout for long double?

-- Gaby