gcc/config/i386/crtprec.c

   1 /*
   2  * Copyright (C) 2007 Free Software Foundation, Inc.
   3  *
   4  * This file is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License as published by the
   6  * Free Software Foundation; either version 2, or (at your option) any
   7  * later version.
   8  *
   9  * In addition to the permissions in the GNU General Public License, the
  10  * Free Software Foundation gives you unlimited permission to link the
  11  * compiled version of this file with other programs, and to distribute
  12  * those programs without any restriction coming from the use of this
  13  * file.  (The General Public License restrictions do apply in other
  14  * respects; for example, they cover modification of the file, and
  15  * distribution when not linked into another program.)
  16  *
  17  * This file is distributed in the hope that it will be useful, but
  18  * WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20  * General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; see the file COPYING.  If not, write to
  24  * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  25  * Boston, MA 02110-1301, USA.
  26  *
  27  *    As a special exception, if you link this library with files
  28  *    compiled with GCC to produce an executable, this does not cause
  29  *    the resulting executable to be covered by the GNU General Public License.
  30  *    This exception does not however invalidate any other reasons why
  31  *    the executable file might be covered by the GNU General Public License.
  32  */
  33
  34 #if __PREC == 32
  35  #define X87CW          (0 << 8)        /* Single precision (24 bits) */
  36 #elif __PREC == 64
  37  #define X87CW          (2 << 8)        /* Double precision (53 bits) */
  38 #elif __PREC == 80
  39  #define X87CW          (3 << 8)        /* Extended precision (64 bits) */
  40 #else
  41  #error "Wrong precision requested."
  42 #endif
  43
  44 #define X87CW_PCMASK    (3 << 8)
  45
  46 static void __attribute__((constructor))
  47 set_precision (void)
  48 {
  49   unsigned short int cwd;
  50
  51   asm volatile ("fstcw\t%0" : "=m" (cwd));
  52
  53   cwd &= ~X87CW_PCMASK;
  54   cwd |= X87CW;
  55
  56   asm volatile ("fldcw\t%0" : : "m" (cwd));
  57 }