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 1.14 2013/11/11 23:57:34 joerg 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 #ifndef __HAVE_LONG_DOUBLE
  31 __strong_alias(_floorl, floor)
  32 __weak_alias(floorl, floor)
  33 #endif
  34
  35 static const double huge = 1.0e300;
  36
  37 double
  38 floor(double x)
  39 {
  40         int32_t i0,i1,jj0;
  41         u_int32_t i,j;
  42         EXTRACT_WORDS(i0,i1,x);
  43         jj0 = ((i0>>20)&0x7ff)-0x3ff;
  44         if(jj0<20) {
  45             if(jj0<0) {         /* raise inexact if x != 0 */
  46                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  47                     if(i0>=0) {i0=i1=0;}
  48                     else if(((i0&0x7fffffff)|i1)!=0)
  49                         { i0=0xbff00000;i1=0;}
  50                 }
  51             } else {
  52                 i = (0x000fffff)>>jj0;
  53                 if(((i0&i)|i1)==0) return x; /* x is integral */
  54                 if(huge+x>0.0) {        /* raise inexact flag */
  55                     if(i0<0) i0 += (0x00100000)>>jj0;
  56                     i0 &= (~i); i1=0;
  57                 }
  58             }
  59         } else if (jj0>51) {
  60             if(jj0==0x400) return x+x;  /* inf or NaN */
  61             else return x;              /* x is integral */
  62         } else {
  63             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  64             if((i1&i)==0) return x;     /* x is integral */
  65             if(huge+x>0.0) {            /* raise inexact flag */
  66                 if(i0<0) {
  67                     if(jj0==20) i0+=1;
  68                     else {
  69                         j = i1+(1<<(52-jj0));
  70                         if(j<(u_int32_t)i1) i0 +=1 ;    /* got a carry */
  71                         i1=j;
  72                     }
  73                 }
  74                 i1 &= (~i);
  75             }
  76         }
  77         INSERT_WORDS(x,i0,i1);
  78         return x;
  79 }