newlib-cygwin/newlib/libm/common/s_trunc.c

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

#include "fdlibm.h"

#ifndef _DOUBLE_IS_32BITS

#ifdef __STDC__
	double trunc(double x)
#else
	double trunc(x)
	double x;
#endif
{
  int signbit;
  /* Most significant word, least significant word. */
  int msw;
  unsigned int lsw;
  int exponent_less_1023;

  EXTRACT_WORDS(msw, lsw, x);

  /* Extract sign bit. */
  signbit = msw & 0x80000000;

  /* Extract exponent field. */
  exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023;

  if (exponent_less_1023 < 20)
    {
      /* All significant digits are in msw. */
      if (exponent_less_1023 < 0)
        {
          /* -1 < x < 1, so result is +0 or -0. */
          INSERT_WORDS(x, signbit, 0);
        }
      else
        {
          /* All relevant fraction bits are in msw, so lsw of the result is 0. */
          INSERT_WORDS(x, signbit | (msw & ~(0x000fffff >> exponent_less_1023)), 0);
        }
    }
  else if (exponent_less_1023 > 51)
    {
      if (exponent_less_1023 == 1024)
        {
          /* x is infinite, or not a number, so trigger an exception. */
          return x + x;
        }
      /* All bits in the fraction fields of the msw and lsw are needed in the result. */
    }
  else
    {
      /* All fraction bits in msw are relevant.  Truncate irrelevant
         bits from lsw. */
      INSERT_WORDS(x, msw, lsw & ~(0xffffffffu >> (exponent_less_1023 - 20)));
    }
  return x;
}

#endif /* _DOUBLE_IS_32BITS */