LibC/Math/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.
 * ====================================================
 */
#include  <LibConfig.h>
#include  <sys/EfiCdefs.h>
#if defined(LIBM_SCCS) && !defined(lint)
__RCSID("$NetBSD: s_floor.c,v 1.11 2002/05/26 22:01:56 wiz Exp $");
#endif

/*
 * 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 "math.h"
#include "math_private.h"

static const double huge = 1.0e300;

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) {  /* 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 = ((u_int32_t)(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((int32_t)j<i1) i0 +=1 ;   /* got a carry */
      i1=j;
        }
    }
    i1 &= (~i);
      }
  }
  INSERT_WORDS(x,i0,i1);
  return x;
}