lib/libm/src/s_floor.c

   1 /* @(#)s_floor.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  *
  12  * $NetBSD: s_floor.c,v 1.11 2002/05/26 22:01:56 wiz Exp $
  13  * $DragonFly: src/lib/libm/src/s_floor.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  14  */
  15
  16 /*
  17  * floor(x)
  18  * Return x rounded toward -inf to integral value
  19  * Method:
  20  *      Bit twiddling.
  21  * Exception:
  22  *      Inexact flag raised if x not equal to floor(x).
  23  */
  24
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const double huge = 1.0e300;
  29
  30 double
  31 floor(double x)
  32 {
  33         int32_t i0,i1,j0;
  34         u_int32_t i,j;
  35         EXTRACT_WORDS(i0,i1,x);
  36         j0 = ((i0>>20)&0x7ff)-0x3ff;
  37         if(j0<20) {
  38             if(j0<0) {  /* raise inexact if x != 0 */
  39                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  40                     if(i0>=0) {i0=i1=0;}
  41                     else if(((i0&0x7fffffff)|i1)!=0)
  42                         { i0=0xbff00000;i1=0;}
  43                 }
  44             } else {
  45                 i = (0x000fffff)>>j0;
  46                 if(((i0&i)|i1)==0) return x; /* x is integral */
  47                 if(huge+x>0.0) {        /* raise inexact flag */
  48                     if(i0<0) i0 += (0x00100000)>>j0;
  49                     i0 &= (~i); i1=0;
  50                 }
  51             }
  52         } else if (j0>51) {
  53             if(j0==0x400) return x+x;   /* inf or NaN */
  54             else return x;              /* x is integral */
  55         } else {
  56             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  57             if((i1&i)==0) return x;     /* x is integral */
  58             if(huge+x>0.0) {            /* raise inexact flag */
  59                 if(i0<0) {
  60                     if(j0==20) i0+=1;
  61                     else {
  62                         j = i1+(1<<(52-j0));
  63                         if(j<i1) i0 +=1 ;       /* got a carry */
  64                         i1=j;
  65                     }
  66                 }
  67                 i1 &= (~i);
  68             }
  69         }
  70         INSERT_WORDS(x,i0,i1);
  71         return x;
  72 }