libgcc/config/arm/fp16.c

   1 /* Half-float conversion routines.
   2
   3    Copyright (C) 2008-2014 Free Software Foundation, Inc.
   4    Contributed by CodeSourcery.
   5
   6    This file is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by the
   8    Free Software Foundation; either version 3, or (at your option) any
   9    later version.
  10
  11    This file is distributed in the hope that it will be useful, but
  12    WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    General Public License for more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 static inline unsigned short
  26 __gnu_f2h_internal(unsigned int a, int ieee)
  27 {
  28   unsigned short sign = (a >> 16) & 0x8000;
  29   int aexp = (a >> 23) & 0xff;
  30   unsigned int mantissa = a & 0x007fffff;
  31   unsigned int mask;
  32   unsigned int increment;
  33
  34   if (aexp == 0xff)
  35     {
  36       if (!ieee)
  37         return sign;
  38       return sign | 0x7e00 | (mantissa >> 13);
  39     }
  40
  41   if (aexp == 0 && mantissa == 0)
  42     return sign;
  43
  44   aexp -= 127;
  45
  46   /* Decimal point between bits 22 and 23.  */
  47   mantissa |= 0x00800000;
  48   if (aexp < -14)
  49     {
  50       mask = 0x00ffffff;
  51       if (aexp >= -25)
  52         mask >>= 25 + aexp;
  53     }
  54   else
  55     mask = 0x00001fff;
  56
  57   /* Round.  */
  58   if (mantissa & mask)
  59     {
  60       increment = (mask + 1) >> 1;
  61       if ((mantissa & mask) == increment)
  62         increment = mantissa & (increment << 1);
  63       mantissa += increment;
  64       if (mantissa >= 0x01000000)
  65         {
  66           mantissa >>= 1;
  67           aexp++;
  68         }
  69     }
  70
  71   if (ieee)
  72     {
  73       if (aexp > 15)
  74         return sign | 0x7c00;
  75     }
  76   else
  77     {
  78       if (aexp > 16)
  79         return sign | 0x7fff;
  80     }
  81
  82   if (aexp < -24)
  83     return sign;
  84
  85   if (aexp < -14)
  86     {
  87       mantissa >>= -14 - aexp;
  88       aexp = -14;
  89     }
  90
  91   /* We leave the leading 1 in the mantissa, and subtract one
  92      from the exponent bias to compensate.  */
  93   return sign | (((aexp + 14) << 10) + (mantissa >> 13));
  94 }
  95
  96 unsigned int
  97 __gnu_h2f_internal(unsigned short a, int ieee)
  98 {
  99   unsigned int sign = (unsigned int)(a & 0x8000) << 16;
 100   int aexp = (a >> 10) & 0x1f;
 101   unsigned int mantissa = a & 0x3ff;
 102
 103   if (aexp == 0x1f && ieee)
 104     return sign | 0x7f800000 | (mantissa << 13);
 105
 106   if (aexp == 0)
 107     {
 108       int shift;
 109
 110       if (mantissa == 0)
 111         return sign;
 112
 113       shift = __builtin_clz(mantissa) - 21;
 114       mantissa <<= shift;
 115       aexp = -shift;
 116     }
 117
 118   return sign | (((aexp + 0x70) << 23) + (mantissa << 13));
 119 }
 120
 121 unsigned short
 122 __gnu_f2h_ieee(unsigned int a)
 123 {
 124   return __gnu_f2h_internal(a, 1);
 125 }
 126
 127 unsigned int
 128 __gnu_h2f_ieee(unsigned short a)
 129 {
 130   return __gnu_h2f_internal(a, 1);
 131 }
 132
 133 unsigned short
 134 __gnu_f2h_alternative(unsigned int x)
 135 {
 136   return __gnu_f2h_internal(x, 0);
 137 }
 138
 139 unsigned int
 140 __gnu_h2f_alternative(unsigned short a)
 141 {
 142   return __gnu_h2f_internal(a, 0);
 143 }