fesetenv.c

glibc 库, 不仅可以学习使用库函数,还可以学习函数的具体实现,是提高功力的好资料

/* Install given floating-point environment.
   Copyright (C) 1997,99,2000,01,02,07 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <fenv_libc.h>
#include <bp-sym.h>

int
__fesetenv (const fenv_t *envp)
{
  fenv_union_t old, new;

  /* get the currently set exceptions.  */
  new.fenv = *envp;
  old.fenv = fegetenv_register ();
  
  /* If the old env has no eabled exceptions and the new env has any enabled
     exceptions, then unmask SIGFPE in the MSR FE0/FE1 bits.  This will put
     the hardware into "precise mode" and may cause the FPU to run slower on
     some hardware.  */
  if ((old.l[1] & 0x000000F8) == 0 && (new.l[1] & 0x000000F8) != 0)
    (void)__fe_nomask_env ();
  
  /* If the old env had any eabled exceptions and the new env has no enabled
     exceptions, then mask SIGFPE in the MSR FE0/FE1 bits.  This may allow the
     FPU to run faster because it always takes the default action and can not 
     generate SIGFPE. */
  if ((old.l[1] & 0x000000F8) != 0 && (new.l[1] & 0x000000F8) == 0)
    (void)__fe_mask_env ();
    
  fesetenv_register (*envp);

  /* Success.  */
  return 0;
}

#include <shlib-compat.h>
#if SHLIB_COMPAT (libm, GLIBC_2_1, GLIBC_2_2)
strong_alias (__fesetenv, __old_fesetenv)
compat_symbol (libm, BP_SYM (__old_fesetenv), BP_SYM (fesetenv), GLIBC_2_1);
#endif

libm_hidden_ver (__fesetenv, fesetenv)
versioned_symbol (libm, BP_SYM (__fesetenv), BP_SYM (fesetenv), GLIBC_2_2);