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 1.13 2009/02/16 01:27:36 lukem Exp $
  13  */
  14
  15 /*
  16  * floor(x)
  17  * Return x rounded toward -inf to integral value
  18  * Method:
  19  *      Bit twiddling.
  20  * Exception:
  21  *      Inexact flag raised if x not equal to floor(x).
  22  */
  23
  24 #include <math.h>
  25 #include "math_private.h"
  26
  27 static const double huge = 1.0e300;
  28
  29 double
  30 floor(double x)
  31 {
  32         int32_t i0,i1,jj0;
  33         u_int32_t i,j;
  34         EXTRACT_WORDS(i0,i1,x);
  35         jj0 = ((i0>>20)&0x7ff)-0x3ff;
  36         if(jj0<20) {
  37             if(jj0<0) {         /* raise inexact if x != 0 */
  38                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  39                     if(i0>=0) {i0=i1=0;}
  40                     else if(((i0&0x7fffffff)|i1)!=0)
  41                         { i0=0xbff00000;i1=0;}
  42                 }
  43             } else {
  44                 i = (0x000fffff)>>jj0;
  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)>>jj0;
  48                     i0 &= (~i); i1=0;
  49                 }
  50             }
  51         } else if (jj0>51) {
  52             if(jj0==0x400) return x+x;  /* inf or NaN */
  53             else return x;              /* x is integral */
  54         } else {
  55             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  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(jj0==20) i0+=1;
  60                     else {
  61                         j = i1+(1<<(52-jj0));
  62                         if(j<(u_int32_t)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 }