gcc/config/i386/crtprec.c

   1 /*
   2  * Copyright (C) 2007, 2009 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 3, or (at your option) any
   7  * later version.
   8  *
   9  * This file is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * Under Section 7 of GPL version 3, you are granted additional
  15  * permissions described in the GCC Runtime Library Exception, version
  16  * 3.1, as published by the Free Software Foundation.
  17  *
  18  * You should have received a copy of the GNU General Public License and
  19  * a copy of the GCC Runtime Library Exception along with this program;
  20  * see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  21  * <http://www.gnu.org/licenses/>.
  22  */
  23
  24 #if __PREC == 32
  25  #define X87CW          (0 << 8)        /* Single precision (24 bits) */
  26 #elif __PREC == 64
  27  #define X87CW          (2 << 8)        /* Double precision (53 bits) */
  28 #elif __PREC == 80
  29  #define X87CW          (3 << 8)        /* Extended precision (64 bits) */
  30 #else
  31  #error "Wrong precision requested."
  32 #endif
  33
  34 #define X87CW_PCMASK    (3 << 8)
  35
  36 static void __attribute__((constructor))
  37 set_precision (void)
  38 {
  39   unsigned short int cwd;
  40
  41   asm volatile ("fstcw\t%0" : "=m" (cwd));
  42
  43   cwd &= ~X87CW_PCMASK;
  44   cwd |= X87CW;
  45
  46   asm volatile ("fldcw\t%0" : : "m" (cwd));
  47 }