[Bug c++/106652] [C++23] P1467 - Extended floating-point types and standard names

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106652

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #53557|0                           |1
        is obsolete|                            |
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org
   Last reconfirmed|                            |2022-09-10
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 53558
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53558&action=edit
gcc13-pr106652.patch

The other conversion better should use backend support if available, but
could be implemented in libgcc __truncsfbf2 or inline.  I believe Intel docs
document it as
__bf16
__truncsfbf2 (_Float32 x)
{
  unsigned int y;
  memcpy (&y, &x, sizeof (y));
  unsigned int z = x & 0x7fffffff;
  unsigned short r;
  __bf16 ret;
  if (z < 0x800000)
    // Zero or denormal, flush to zero.
    r = (x & 0x80000000) >> 16;
  else if (z < 0x7f800000)
    // Normal, round to nearest.
    r = (x + 0x7fff + ((x >> 16) & 1)) >> 16;
  else if (z == 0x7f800000)
    // Inf.
    r = x >> 16;
  else
    // NaN.
    r = (x >> 16) | (1 << 6);
  memcpy (&ret, &r, sizeof (r));
  return ret;
}