libgcc/soft-fp/truncbfhf2.c

   1 /* Software floating-point emulation.
   2    Truncate bfloat16 into IEEE half.
   3    Copyright (C) 2022 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    In addition to the permissions in the GNU Lesser General Public
  12    License, the Free Software Foundation gives you unlimited
  13    permission to link the compiled version of this file into
  14    combinations with other programs, and to distribute those
  15    combinations without any restriction coming from the use of this
  16    file.  (The Lesser General Public License restrictions do apply in
  17    other respects; for example, they cover modification of the file,
  18    and distribution when not linked into a combine executable.)
  19
  20    The GNU C Library is distributed in the hope that it will be useful,
  21    but WITHOUT ANY WARRANTY; without even the implied warranty of
  22    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  23    Lesser General Public License for more details.
  24
  25    You should have received a copy of the GNU Lesser General Public
  26    License along with the GNU C Library; if not, see
  27    <http://www.gnu.org/licenses/>.  */
  28
  29 #include "soft-fp.h"
  30 #include "half.h"
  31 #include "brain.h"
  32 #include "single.h"
  33
  34 /* BFtype and HFtype are unordered, neither is a superset or subset
  35    of each other.  Convert BFtype to SFtype (lossless) and then
  36    truncate to HFtype.  */
  37
  38 HFtype
  39 __truncbfhf2 (BFtype a)
  40 {
  41   FP_DECL_EX;
  42   FP_DECL_H (A);
  43   FP_DECL_S (B);
  44   FP_DECL_B (R);
  45   SFtype b;
  46   HFtype r;
  47
  48   FP_INIT_ROUNDMODE;
  49   /* Optimize BFtype to SFtype conversion to simple left shift
  50      by 16 if possible, we don't need to raise exceptions on sNaN
  51      here as the SFtype to HFtype truncation should do that too.  */
  52   if (sizeof (BFtype) == 2
  53       && sizeof (unsigned short) == 2
  54       && sizeof (SFtype) == 4
  55       && sizeof (unsigned int) == 4)
  56     {
  57       union { BFtype a; unsigned short b; } u1;
  58       union { SFtype a; unsigned int b; } u2;
  59       u1.a = a;
  60       u2.b = (u1.b << 8) << 8;
  61       b = u2.a;
  62     }
  63   else
  64     {
  65       FP_UNPACK_RAW_B (A, a);
  66       FP_EXTEND (S, B, 1, 1, B, A);
  67       FP_PACK_RAW_S (b, B);
  68     }
  69   FP_UNPACK_SEMIRAW_S (B, b);
  70   FP_TRUNC (H, S, 1, 1, R, B);
  71   FP_PACK_SEMIRAW_H (r, R);
  72   FP_HANDLE_EXCEPTIONS;
  73
  74   return r;
  75 }