lib/libm/src/s_ceil.c

   1 /* @(#)s_ceil.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_ceil.c,v 1.11 2002/05/26 22:01:54 wiz Exp $
  13  * $DragonFly: src/lib/libm/src/s_ceil.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  14  */
  15
  16 /*
  17  * ceil(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 ceil(x).
  23  */
  24
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const double huge = 1.0e300;
  29
  30 double
  31 ceil(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=0x80000000;i1=0;}
  41                     else if((i0|i1)!=0) { i0=0x3ff00000;i1=0;}
  42                 }
  43             } else {
  44                 i = (0x000fffff)>>j0;
  45                 if(((i0&i)|i1)==0) return x; /* x is integral */
  46                 if(huge+x>0.0) {        /* raise inexact flag */
  47                     if(i0>0) i0 += (0x00100000)>>j0;
  48                     i0 &= (~i); i1=0;
  49                 }
  50             }
  51         } else if (j0>51) {
  52             if(j0==0x400) return x+x;   /* inf or NaN */
  53             else return x;              /* x is integral */
  54         } else {
  55             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  56             if((i1&i)==0) return x;     /* x is integral */
  57             if(huge+x>0.0) {            /* raise inexact flag */
  58                 if(i0>0) {
  59                     if(j0==20) i0+=1;
  60                     else {
  61                         j = i1 + (1<<(52-j0));
  62                         if(j<i1) i0+=1; /* got a carry */
  63                         i1 = j;
  64                     }
  65                 }
  66                 i1 &= (~i);
  67             }
  68         }
  69         INSERT_WORDS(x,i0,i1);
  70         return x;
  71 }