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
  13 #include <sys/cdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_floor.c,v 1.13 2009/02/16 01:27:36 lukem Exp $");
  16 #endif
  17
  18 /*
  19  * floor(x)
  20  * Return x rounded toward -inf to integral value
  21  * Method:
  22  *      Bit twiddling.
  23  * Exception:
  24  *      Inexact flag raised if x not equal to floor(x).
  25  */
  26
  27 #include "math.h"
  28 #include "math_private.h"
  29
  30 static const double huge = 1.0e300;
  31
  32 double
  33 floor(double x)
  34 {
  35         int32_t i0,i1,jj0;
  36         u_int32_t i,j;
  37         EXTRACT_WORDS(i0,i1,x);
  38         jj0 = ((i0>>20)&0x7ff)-0x3ff;
  39         if(jj0<20) {
  40             if(jj0<0) {         /* raise inexact if x != 0 */
  41                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  42                     if(i0>=0) {i0=i1=0;}
  43                     else if(((i0&0x7fffffff)|i1)!=0)
  44                         { i0=0xbff00000;i1=0;}
  45                 }
  46             } else {
  47                 i = (0x000fffff)>>jj0;
  48                 if(((i0&i)|i1)==0) return x; /* x is integral */
  49                 if(huge+x>0.0) {        /* raise inexact flag */
  50                     if(i0<0) i0 += (0x00100000)>>jj0;
  51                     i0 &= (~i); i1=0;
  52                 }
  53             }
  54         } else if (jj0>51) {
  55             if(jj0==0x400) return x+x;  /* inf or NaN */
  56             else return x;              /* x is integral */
  57         } else {
  58             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  59             if((i1&i)==0) return x;     /* x is integral */
  60             if(huge+x>0.0) {            /* raise inexact flag */
  61                 if(i0<0) {
  62                     if(jj0==20) i0+=1;
  63                     else {
  64                         j = i1+(1<<(52-jj0));
  65                         if(j<(u_int32_t)i1) i0 +=1 ;    /* got a carry */
  66                         i1=j;
  67                     }
  68                 }
  69                 i1 &= (~i);
  70             }
  71         }
  72         INSERT_WORDS(x,i0,i1);
  73         return x;
  74 }