libm/s_floor.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /*
  13  * floor(x)
  14  * Return x rounded toward -inf to integral value
  15  * Method:
  16  *      Bit twiddling.
  17  * Exception:
  18  *      Inexact flag raised if x not equal to floor(x).
  19  */
  20
  21 #include <features.h>
  22 /* Prevent math.h from defining a colliding inline */
  23 #undef __USE_EXTERN_INLINES
  24 #include "math.h"
  25 #include "math_private.h"
  26
  27 static const double huge = 1.0e300;
  28
  29 double floor(double x)
  30 {
  31         int32_t i0,i1,_j0;
  32         u_int32_t i,j;
  33         EXTRACT_WORDS(i0,i1,x);
  34         _j0 = ((i0>>20)&0x7ff)-0x3ff;
  35         if(_j0<20) {
  36             if(_j0<0) {         /* raise inexact if x != 0 */
  37                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  38                     if(i0>=0) {i0=i1=0;}
  39                     else if(((i0&0x7fffffff)|i1)!=0)
  40                         { i0=0xbff00000;i1=0;}
  41                 }
  42             } else {
  43                 i = (0x000fffff)>>_j0;
  44                 if(((i0&i)|i1)==0) return x; /* x is integral */
  45                 if(huge+x>0.0) {        /* raise inexact flag */
  46                     if(i0<0) i0 += (0x00100000)>>_j0;
  47                     i0 &= (~i); i1=0;
  48                 }
  49             }
  50         } else if (_j0>51) {
  51             if(_j0==0x400) return x+x;  /* inf or NaN */
  52             else return x;              /* x is integral */
  53         } else {
  54             i = ((u_int32_t)(0xffffffff))>>(_j0-20);
  55             if((i1&i)==0) return x;     /* x is integral */
  56             if(huge+x>0.0) {            /* raise inexact flag */
  57                 if(i0<0) {
  58                     if(_j0==20) i0+=1;
  59                     else {
  60                         j = i1+(1<<(52-_j0));
  61                         if(j<i1) i0 +=1 ;       /* got a carry */
  62                         i1=j;
  63                     }
  64                 }
  65                 i1 &= (~i);
  66             }
  67         }
  68         INSERT_WORDS(x,i0,i1);
  69         return x;
  70 }
  71 libm_hidden_def(floor)