glibc/sysdeps/ieee754/dbl-64/s_floor.c

/* @(#)s_floor.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/*
 * floor(x)
 * Return x rounded toward -inf to integral value
 * Method:
 *	Bit twiddling.
 */

#include <math.h>
#include <math_private.h>

double
__floor (double x)
{
  int32_t i0, i1, j0;
  u_int32_t i, j;
  EXTRACT_WORDS (i0, i1, x);
  j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  if (j0 < 20)
    {
      if (j0 < 0)
	{
	  /* return 0*sign(x) if |x|<1 */
	  if (i0 >= 0)
	    {
	      i0 = i1 = 0;
	    }
	  else if (((i0 & 0x7fffffff) | i1) != 0)
	    {
	      i0 = 0xbff00000; i1 = 0;
	    }
	}
      else
	{
	  i = (0x000fffff) >> j0;
	  if (((i0 & i) | i1) == 0)
	    return x;                        /* x is integral */
	  if (i0 < 0)
	    i0 += (0x00100000) >> j0;
	  i0 &= (~i); i1 = 0;
	}
    }
  else if (j0 > 51)
    {
      if (j0 == 0x400)
	return x + x;                   /* inf or NaN */
      else
	return x;                       /* x is integral */
    }
  else
    {
      i = ((u_int32_t) (0xffffffff)) >> (j0 - 20);
      if ((i1 & i) == 0)
	return x;                       /* x is integral */
      if (i0 < 0)
	{
	  if (j0 == 20)
	    i0 += 1;
	  else
	    {
	      j = i1 + (1 << (52 - j0));
	      if (j < i1)
		i0 += 1;                /* got a carry */
	      i1 = j;
	    }
	}
      i1 &= (~i);
    }
  INSERT_WORDS (x, i0, i1);
  return x;
}
#ifndef __floor
weak_alias (__floor, floor)
# ifdef NO_LONG_DOUBLE
strong_alias (__floor, __floorl)
weak_alias (__floor, floorl)
# endif
#endif