prime/src/Runtime/s_floor.c

/* @(#)s_floor.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, 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.
 * Exception:
 *	Inexact flag raised if x not equal to floor(x).
 */
#include "fdlibm.h"

#ifdef __STDC__
static const double huge = 1.0e300;
#else
static double huge = 1.0e300;
#endif

#ifdef __STDC__
double floor(double x)
#else
double floor(x)
double x;
#endif
{
  int i0, i1, j0;
  unsigned i, j;
  i0 = __HI(x);
  i1 = __LO(x);
  j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  if (j0 < 20) {
    if (j0 < 0) {           /* raise inexact if x != 0 */
      if (huge + x > 0.0) { /* 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 (huge + x > 0.0) { /* raise inexact flag */
        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 = ((unsigned)(0xffffffff)) >> (j0 - 20);
    if ((i1 & i) == 0)
      return x;           /* x is integral */
    if (huge + x > 0.0) { /* raise inexact flag */
      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);
    }
  }
  __HI(x) = i0;
  __LO(x) = i1;
  return x;
}