https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88074
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jsm28 at gcc dot gnu.org
--- Comment #16 from Richard Biener <rguenth at gcc dot gnu.org> ---
So based on some code in the Fortran FE I used
machine_mode mode;
int min_exp = -1;
int max_exp = 1;
FOR_EACH_MODE_IN_CLASS (mode, MODE_FLOAT)
if (SCALAR_FLOAT_MODE_P (mode))
{
const real_format *fmt = REAL_MODE_FORMAT (mode);
if (fmt)
{
if (fmt->emin < min_exp)
min_exp = fmt->emin - fmt->p + 1;
^^^
if (fmt->emax > max_exp)
max_exp = fmt->emax;
}
}
if (mpfr_set_emin (min_exp)
|| mpfr_set_emax (max_exp))
sorry ("mpfr not configured to handle all float modes");
but that ICEs in real_to_decimal_for_mode for the float128*.c tests for
example for 6.47517511943802511092443895822764655e-4966. The real
number has an exponent of -16493 but the format is
$17 = {encode =
0x103a237 <encode_ieee_extended_intel_128(real_format const*, long*,
real_value const*)>, decode =
0x103a5b3 <decode_ieee_extended_intel_128(real_format const*, real_value*,
long const*)>, b = 2, p = 64, pnan = 64, emin = -16381, emax = 16384,
signbit_ro = 79, signbit_rw = 79, ieee_bits = 65,
round_towards_zero = false, has_sign_dependent_rounding = true,
has_nans = true, has_inf = true, has_denorm = true, has_signed_zero = true,
qnan_msb_set = true, canonical_nan_lsbs_set = false,
name = 0x21f3a60 "ieee_extended_intel_128"}
so somehow the formula fmt->emin - fmt->p + 1 isn't sufficient (that's
used for Fortrans "denormalization"). Given I use a global emin/emax
independent on the modes of the actual constant folding (just to limit
computational effort in mpfr) I can of course simply apply a factor of two
for safety but what's special about ieee_extended_intel_128 here?
(the number is __FLT128_DENORM_MIN__).
Joseph, what's the magic with fmt->emin and denormals? The subtraction
of fmt->p should have accounted for all?
