lib/libm/src/s_trunc.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 0
  15 __FBSDID("$FreeBSD: src/lib/msun/src/s_trunc.c,v 1.1 2004/06/20 09:25:43 das Exp $");
  16 #endif
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 __RCSID("$NetBSD: s_trunc.c,v 1.3 2008/04/25 22:21:53 christos Exp $");
  19 #endif
  20
  21 /*
  22  * trunc(x)
  23  * Return x rounded toward 0 to integral value
  24  * Method:
  25  *      Bit twiddling.
  26  * Exception:
  27  *      Inexact flag raised if x not equal to trunc(x).
  28  */
  29
  30 #include "math.h"
  31 #include "math_private.h"
  32
  33 static const double huge = 1.0e300;
  34
  35 double
  36 trunc(double x)
  37 {
  38         int32_t i0,i1,jj0;
  39         uint32_t i;
  40         EXTRACT_WORDS(i0,i1,x);
  41         jj0 = ((i0>>20)&0x7ff)-0x3ff;
  42         if(jj0<20) {
  43             if(jj0<0) {         /* raise inexact if x != 0 */
  44                 if(huge+x>0.0) {/* |x|<1, so return 0*sign(x) */
  45                     i0 &= 0x80000000U;
  46                     i1 = 0;
  47                 }
  48             } else {
  49                 i = (0x000fffff)>>jj0;
  50                 if(((i0&i)|i1)==0) return x; /* x is integral */
  51                 if(huge+x>0.0) {        /* raise inexact flag */
  52                     i0 &= (~i); i1=0;
  53                 }
  54             }
  55         } else if (jj0>51) {
  56             if(jj0==0x400) return x+x;  /* inf or NaN */
  57             else return x;              /* x is integral */
  58         } else {
  59             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  60             if((i1&i)==0) return x;     /* x is integral */
  61             if(huge+x>0.0)              /* raise inexact flag */
  62                 i1 &= (~i);
  63         }
  64         INSERT_WORDS(x,i0,i1);
  65         return x;
  66 }