compiler/stdc/math/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
  13 #ifndef lint
  14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_floor.c,v 1.9 2003/07/23 04:53:46 peter Exp $";
  15 #endif
  16
  17 /*
  18  * floor(x)
  19  * Return x rounded toward -inf to integral value
  20  * Method:
  21  *      Bit twiddling.
  22  * Exception:
  23  *      Inexact flag raised if x not equal to floor(x).
  24  */
  25
  26 #include "math.h"
  27 #include "math_private.h"
  28
  29 static const double huge = 1.0e300;
  30
  31 double
  32 floor(double x)
  33 {
  34         int32_t i0,i1,j0;
  35         uint32_t i,j;
  36         EXTRACT_WORDS(i0,i1,x);
  37         j0 = ((i0>>20)&0x7ff)-0x3ff;
  38         if(j0<20) {
  39             if(j0<0) {  /* raise inexact if x != 0 */
  40                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  41                     if(i0>=0) {i0=i1=0;}
  42                     else if(((i0&0x7fffffff)|i1)!=0)
  43                         { i0=0xbff00000;i1=0;}
  44                 }
  45             } else {
  46                 i = (0x000fffff)>>j0;
  47                 if(((i0&i)|i1)==0) return x; /* x is integral */
  48                 if(huge+x>0.0) {        /* raise inexact flag */
  49                     if(i0<0) i0 += (0x00100000)>>j0;
  50                     i0 &= (~i); i1=0;
  51                 }
  52             }
  53         } else if (j0>51) {
  54             if(j0==0x400) return x+x;   /* inf or NaN */
  55             else return x;              /* x is integral */
  56         } else {
  57             i = ((uint32_t)(0xffffffff))>>(j0-20);
  58             if((i1&i)==0) return x;     /* x is integral */
  59             if(huge+x>0.0) {            /* raise inexact flag */
  60                 if(i0<0) {
  61                     if(j0==20) i0+=1;
  62                     else {
  63                         j = i1+(1<<(52-j0));
  64                         if(j<i1) i0 +=1 ;       /* got a carry */
  65                         i1=j;
  66                     }
  67                 }
  68                 i1 &= (~i);
  69             }
  70         }
  71         INSERT_WORDS(x,i0,i1);
  72         return x;
  73 }