libgcc/config/arm/fp16.c

   1 /* Half-float conversion routines.
   2
   3    Copyright (C) 2008-2015 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       if (mantissa == 0)
  39         return sign | 0x7c00;   /* Infinity.  */
  40       /* Remaining cases are NaNs.  Convert SNaN to QNaN.  */
  41       return sign | 0x7e00 | (mantissa >> 13);
  42     }
  43
  44   if (aexp == 0 && mantissa == 0)
  45     return sign;
  46
  47   aexp -= 127;
  48
  49   /* Decimal point between bits 22 and 23.  */
  50   mantissa |= 0x00800000;
  51   if (aexp < -14)
  52     {
  53       mask = 0x00ffffff;
  54       if (aexp >= -25)
  55         mask >>= 25 + aexp;
  56     }
  57   else
  58     mask = 0x00001fff;
  59
  60   /* Round.  */
  61   if (mantissa & mask)
  62     {
  63       increment = (mask + 1) >> 1;
  64       if ((mantissa & mask) == increment)
  65         increment = mantissa & (increment << 1);
  66       mantissa += increment;
  67       if (mantissa >= 0x01000000)
  68         {
  69           mantissa >>= 1;
  70           aexp++;
  71         }
  72     }
  73
  74   if (ieee)
  75     {
  76       if (aexp > 15)
  77         return sign | 0x7c00;
  78     }
  79   else
  80     {
  81       if (aexp > 16)
  82         return sign | 0x7fff;
  83     }
  84
  85   if (aexp < -24)
  86     return sign;
  87
  88   if (aexp < -14)
  89     {
  90       mantissa >>= -14 - aexp;
  91       aexp = -14;
  92     }
  93
  94   /* We leave the leading 1 in the mantissa, and subtract one
  95      from the exponent bias to compensate.  */
  96   return sign | (((aexp + 14) << 10) + (mantissa >> 13));
  97 }
  98
  99 unsigned int
 100 __gnu_h2f_internal(unsigned short a, int ieee)
 101 {
 102   unsigned int sign = (unsigned int)(a & 0x8000) << 16;
 103   int aexp = (a >> 10) & 0x1f;
 104   unsigned int mantissa = a & 0x3ff;
 105
 106   if (aexp == 0x1f && ieee)
 107     return sign | 0x7f800000 | (mantissa << 13);
 108
 109   if (aexp == 0)
 110     {
 111       int shift;
 112
 113       if (mantissa == 0)
 114         return sign;
 115
 116       shift = __builtin_clz(mantissa) - 21;
 117       mantissa <<= shift;
 118       aexp = -shift;
 119     }
 120
 121   return sign | (((aexp + 0x70) << 23) + (mantissa << 13));
 122 }
 123
 124 unsigned short
 125 __gnu_f2h_ieee(unsigned int a)
 126 {
 127   return __gnu_f2h_internal(a, 1);
 128 }
 129
 130 unsigned int
 131 __gnu_h2f_ieee(unsigned short a)
 132 {
 133   return __gnu_h2f_internal(a, 1);
 134 }
 135
 136 unsigned short
 137 __gnu_f2h_alternative(unsigned int x)
 138 {
 139   return __gnu_f2h_internal(x, 0);
 140 }
 141
 142 unsigned int
 143 __gnu_h2f_alternative(unsigned short a)
 144 {
 145   return __gnu_h2f_internal(a, 0);
 146 }