src/math/trunc.c

   1 /* origin: FreeBSD /usr/src/lib/msun/src/s_trunc.c */
   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  * trunc(x)
  14  * Return x rounded toward 0 to integral value
  15  * Method:
  16  *      Bit twiddling.
  17  * Exception:
  18  *      Inexact flag raised if x not equal to trunc(x).
  19  */
  20
  21 #include "libm.h"
  22
  23 static const double huge = 1.0e300;
  24
  25 double trunc(double x)
  26 {
  27         int32_t i0,i1,j0;
  28         uint32_t i;
  29
  30         EXTRACT_WORDS(i0, i1, x);
  31         j0 = ((i0>>20)&0x7ff) - 0x3ff;
  32         if (j0 < 20) {
  33                 if (j0 < 0) { /* |x|<1, return 0*sign(x) */
  34                         /* raise inexact if x != 0 */
  35                         if (huge+x > 0.0) {
  36                                 i0 &= 0x80000000U;
  37                                 i1 = 0;
  38                         }
  39                 } else {
  40                         i = 0x000fffff>>j0;
  41                         if (((i0&i)|i1) == 0)
  42                                 return x; /* x is integral */
  43                         /* raise inexact */
  44                         if (huge+x > 0.0) {
  45                                 i0 &= ~i;
  46                                 i1 = 0;
  47                         }
  48                 }
  49         } else if (j0 > 51) {
  50                 if (j0 == 0x400)
  51                         return x + x;  /* inf or NaN */
  52                 return x;              /* x is integral */
  53         } else {
  54                 i = (uint32_t)0xffffffff>>(j0-20);
  55                 if ((i1&i) == 0)
  56                         return x;      /* x is integral */
  57                 /* raise inexact */
  58                 if (huge+x > 0.0)
  59                         i1 &= ~i;
  60         }
  61         INSERT_WORDS(x, i0, i1);
  62         return x;
  63 }