s_ceil.c

来自「Glibc 2.3.2源代码(解压后有100多M)」· C语言 代码 · 共 55 行

/* Copyright (C) 1998, 2000 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Richard Henderson.

   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 <math.h>

/* Use the -inf rounding mode conversion instructions to implement
   ceil, via something akin to -floor(-x).  This is much faster than
   playing with the fpcr to achieve +inf rounding mode.  */

double
__ceil (double x)
{
  if (isless (fabs (x), 9007199254740992.0))	/* 1 << DBL_MANT_DIG */
    {
      double tmp1, new_x;

      new_x = -x;
      __asm (
#ifdef _IEEE_FP_INEXACT
	     "cvttq/svim %2,%1\n\t"
#else
	     "cvttq/svm %2,%1\n\t"
#endif
	     "cvtqt/m %1,%0\n\t"
	     : "=f"(new_x), "=&f"(tmp1)
	     : "f"(new_x));

      /* Fix up the negation we did above, as well as handling -0 properly. */
      x = copysign(new_x, x);
    }
  return x;
}

weak_alias (__ceil, ceil)
#ifdef NO_LONG_DOUBLE
strong_alias (__ceil, __ceill)
weak_alias (__ceil, ceill)
#endif