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  * $NetBSD: s_trunc.c,v 1.2 2007/01/17 23:24:22 hubertf Exp $
  13  * $DragonFly: src/lib/libm/src/s_trunc.c,v 1.1 2007/06/17 06:26:18 pavalos Exp $
  14  */
  15
  16 /*
  17  * trunc(x)
  18  * Return x rounded toward 0 to integral value
  19  * Method:
  20  *      Bit twiddling.
  21  * Exception:
  22  *      Inexact flag raised if x not equal to trunc(x).
  23  */
  24
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const double huge = 1.0e300;
  29
  30 double
  31 trunc(double x)
  32 {
  33         int32_t i0,i1,j00;
  34         uint32_t i;
  35         EXTRACT_WORDS(i0,i1,x);
  36         j00 = ((i0>>20)&0x7ff)-0x3ff;
  37         if(j00<20) {
  38             if(j00<0) {         /* raise inexact if x != 0 */
  39                 if(huge+x>0.0) {/* |x|<1, so return 0*sign(x) */
  40                     i0 &= 0x80000000U;
  41                     i1 = 0;
  42                 }
  43             } else {
  44                 i = (0x000fffff)>>j00;
  45                 if(((i0&i)|i1)==0) return x; /* x is integral */
  46                 if(huge+x>0.0) {        /* raise inexact flag */
  47                     i0 &= (~i); i1=0;
  48                 }
  49             }
  50         } else if (j00>51) {
  51             if(j00==0x400) return x+x;  /* inf or NaN */
  52             else return x;              /* x is integral */
  53         } else {
  54             i = ((u_int32_t)(0xffffffff))>>(j00-20);
  55             if((i1&i)==0) return x;     /* x is integral */
  56             if(huge+x>0.0)              /* raise inexact flag */
  57                 i1 &= (~i);
  58         }
  59         INSERT_WORDS(x,i0,i1);
  60         return x;
  61 }