compiler/stdc/math/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 __FBSDID("$FreeBSD: src/lib/msun/src/s_trunc.c,v 1.1 2004/06/20 09:25:43 das Exp $");
  14
  15 /*
  16  * trunc(x)
  17  * Return x rounded toward 0 to integral value
  18  * Method:
  19  *      Bit twiddling.
  20  * Exception:
  21  *      Inexact flag raised if x not equal to trunc(x).
  22  */
  23
  24 #include "math.h"
  25 #include "math_private.h"
  26
  27 static const double huge = 1.0e300;
  28
  29 double
  30 trunc(double x)
  31 {
  32         int32_t i0,i1,j0;
  33         uint32_t i;
  34         EXTRACT_WORDS(i0,i1,x);
  35         j0 = ((i0>>20)&0x7ff)-0x3ff;
  36         if(j0<20) {
  37             if(j0<0) {  /* raise inexact if x != 0 */
  38                 if(huge+x>0.0) {/* |x|<1, so return 0*sign(x) */
  39                     i0 &= 0x80000000U;
  40                     i1 = 0;
  41                 }
  42             } else {
  43                 i = (0x000fffff)>>j0;
  44                 if(((i0&i)|i1)==0) return x; /* x is integral */
  45                 if(huge+x>0.0) {        /* raise inexact flag */
  46                     i0 &= (~i); i1=0;
  47                 }
  48             }
  49         } else if (j0>51) {
  50             if(j0==0x400) return x+x;   /* inf or NaN */
  51             else return x;              /* x is integral */
  52         } else {
  53             i = ((uint32_t)(0xffffffff))>>(j0-20);
  54             if((i1&i)==0) return x;     /* x is integral */
  55             if(huge+x>0.0)              /* raise inexact flag */
  56                 i1 &= (~i);
  57         }
  58         INSERT_WORDS(x,i0,i1);
  59         return x;
  60 }