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 1.4 2013/11/13 12:58:11 joerg 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 #ifndef __HAVE_LONG_DOUBLE
  34 __strong_alias(_truncl, trunc)
  35 __weak_alias(truncl, trunc)
  36 #endif
  37
  38 static const double huge = 1.0e300;
  39
  40 double
  41 trunc(double x)
  42 {
  43         int32_t i0,i1,jj0;
  44         uint32_t i;
  45         EXTRACT_WORDS(i0,i1,x);
  46         jj0 = ((i0>>20)&0x7ff)-0x3ff;
  47         if(jj0<20) {
  48             if(jj0<0) {         /* raise inexact if x != 0 */
  49                 if(huge+x>0.0) {/* |x|<1, so return 0*sign(x) */
  50                     i0 &= 0x80000000U;
  51                     i1 = 0;
  52                 }
  53             } else {
  54                 i = (0x000fffff)>>jj0;
  55                 if(((i0&i)|i1)==0) return x; /* x is integral */
  56                 if(huge+x>0.0) {        /* raise inexact flag */
  57                     i0 &= (~i); i1=0;
  58                 }
  59             }
  60         } else if (jj0>51) {
  61             if(jj0==0x400) return x+x;  /* inf or NaN */
  62             else return x;              /* x is integral */
  63         } else {
  64             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  65             if((i1&i)==0) return x;     /* x is integral */
  66             if(huge+x>0.0)              /* raise inexact flag */
  67                 i1 &= (~i);
  68         }
  69         INSERT_WORDS(x,i0,i1);
  70         return x;
  71 }