libhsail-rt/rt/fp16.c

   1 /* Half-float conversion routines.  Code mostly borrowed from the ARM's
   2    builtin function.
   3
   4    Copyright (C) 2008-2017 Free Software Foundation, Inc.
   5    Contributed by CodeSourcery.
   6
   7    This file is free software; you can redistribute it and/or modify it
   8    under the terms of the GNU General Public License as published by the
   9    Free Software Foundation; either version 3, or (at your option) any
  10    later version.
  11
  12    This file is distributed in the hope that it will be useful, but
  13    WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    General Public License for more details.
  16
  17    Under Section 7 of GPL version 3, you are granted additional
  18    permissions described in the GCC Runtime Library Exception, version
  19    3.1, as published by the Free Software Foundation.
  20
  21    You should have received a copy of the GNU General Public License and
  22    a copy of the GCC Runtime Library Exception along with this program;
  23    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  24    <http://www.gnu.org/licenses/>.  */
  25
  26 static inline unsigned short
  27 __gnu_f2h_internal (unsigned int a, int ieee)
  28 {
  29   unsigned short sign = (a >> 16) & 0x8000;
  30   int aexp = (a >> 23) & 0xff;
  31   unsigned int mantissa = a & 0x007fffff;
  32   unsigned int mask;
  33   unsigned int increment;
  34
  35   if (aexp == 0xff)
  36     {
  37       if (!ieee)
  38         return sign;
  39       if (mantissa == 0)
  40         return sign | 0x7c00; /* Infinity.  */
  41       /* Remaining cases are NaNs.  Convert SNaN to QNaN.  */
  42       return sign | 0x7e00 | (mantissa >> 13);
  43     }
  44
  45   if (aexp == 0 && mantissa == 0)
  46     return sign;
  47
  48   aexp -= 127;
  49
  50   /* Decimal point between bits 22 and 23.  */
  51   mantissa |= 0x00800000;
  52   if (aexp < -14)
  53     {
  54       mask = 0x00ffffff;
  55       if (aexp >= -25)
  56         mask >>= 25 + aexp;
  57     }
  58   else
  59     mask = 0x00001fff;
  60
  61   /* Round.  */
  62   if (mantissa & mask)
  63     {
  64       increment = (mask + 1) >> 1;
  65       if ((mantissa & mask) == increment)
  66         increment = mantissa & (increment << 1);
  67       mantissa += increment;
  68       if (mantissa >= 0x01000000)
  69         {
  70           mantissa >>= 1;
  71           aexp++;
  72         }
  73     }
  74
  75   if (ieee)
  76     {
  77       if (aexp > 15)
  78         return sign | 0x7c00;
  79     }
  80   else
  81     {
  82       if (aexp > 16)
  83         return sign | 0x7fff;
  84     }
  85
  86   if (aexp < -24)
  87     return sign;
  88
  89   if (aexp < -14)
  90     {
  91       mantissa >>= -14 - aexp;
  92       aexp = -14;
  93     }
  94
  95   /* We leave the leading 1 in the mantissa, and subtract one
  96      from the exponent bias to compensate.  */
  97   return sign | (((aexp + 14) << 10) + (mantissa >> 13));
  98 }
  99
 100 static unsigned int
 101 __gnu_h2f_internal (unsigned short a, int ieee)
 102 {
 103   unsigned int sign = (unsigned int) (a & 0x8000) << 16;
 104   int aexp = (a >> 10) & 0x1f;
 105   unsigned int mantissa = a & 0x3ff;
 106
 107   if (aexp == 0x1f && ieee)
 108     return sign | 0x7f800000 | (mantissa << 13);
 109
 110   if (aexp == 0)
 111     {
 112       int shift;
 113
 114       if (mantissa == 0)
 115         return sign;
 116
 117       shift = __builtin_clz (mantissa) - 21;
 118       mantissa <<= shift;
 119       aexp = -shift;
 120     }
 121
 122   return sign | (((aexp + 0x70) << 23) + (mantissa << 13));
 123 }
 124
 125 unsigned short
 126 __hsail_f32_to_f16 (unsigned int a)
 127 {
 128   return __gnu_f2h_internal (a, 1);
 129 }
 130
 131 unsigned int
 132 __hsail_f16_to_f32 (unsigned short a)
 133 {
 134   return __gnu_h2f_internal (a, 1);
 135 }