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crtprec.c revision 1.1.1.1 
      1 /*
      2  * Copyright (C) 2007-2013 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 }
     48