libm/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 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: s_floor.c,v 1.8 1995/05/10 20:47:20 jtc 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 #ifdef __STDC__
  30 static const double huge = 1.0e300;
  31 #else
  32 static double huge = 1.0e300;
  33 #endif
  34
  35 libm_hidden_proto(floor)
  36 #ifdef __STDC__
  37         double floor(double x)
  38 #else
  39         double floor(x)
  40         double x;
  41 #endif
  42 {
  43         int32_t i0,i1,j0;
  44         u_int32_t i,j;
  45         EXTRACT_WORDS(i0,i1,x);
  46         j0 = ((i0>>20)&0x7ff)-0x3ff;
  47         if(j0<20) {
  48             if(j0<0) {  /* raise inexact if x != 0 */
  49                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  50                     if(i0>=0) {i0=i1=0;}
  51                     else if(((i0&0x7fffffff)|i1)!=0)
  52                         { i0=0xbff00000;i1=0;}
  53                 }
  54             } else {
  55                 i = (0x000fffff)>>j0;
  56                 if(((i0&i)|i1)==0) return x; /* x is integral */
  57                 if(huge+x>0.0) {        /* raise inexact flag */
  58                     if(i0<0) i0 += (0x00100000)>>j0;
  59                     i0 &= (~i); i1=0;
  60                 }
  61             }
  62         } else if (j0>51) {
  63             if(j0==0x400) return x+x;   /* inf or NaN */
  64             else return x;              /* x is integral */
  65         } else {
  66             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  67             if((i1&i)==0) return x;     /* x is integral */
  68             if(huge+x>0.0) {            /* raise inexact flag */
  69                 if(i0<0) {
  70                     if(j0==20) i0+=1;
  71                     else {
  72                         j = i1+(1<<(52-j0));
  73                         if(j<i1) i0 +=1 ;       /* got a carry */
  74                         i1=j;
  75                     }
  76                 }
  77                 i1 &= (~i);
  78             }
  79         }
  80         INSERT_WORDS(x,i0,i1);
  81         return x;
  82 }
  83 libm_hidden_def(floor)