prime/src/Runtime/s_modf.c

/* @(#)s_modf.c 1.2 95/01/04 */
/*
 * ====================================================
 * 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.
 * ====================================================
 */

/*
 * modf(double x, double *iptr)
 * return fraction part of x, and return x's integral part in *iptr.
 * Method:
 *	Bit twiddling.
 *
 * Exception:
 *	No exception.
 */

#include "fdlibm.h"

#ifdef __STDC__
static const double one = 1.0;
#else
static double one = 1.0;
#endif

#ifdef __STDC__
double modf(double x, double* iptr)
#else
double modf(x, iptr)
double x, *iptr;
#endif
{
  _INT32 i0, i1, j0;
  _UINT32 i;
  i0 = __HI(x);                      /* high x */
  i1 = __LO(x);                      /* low  x */
  j0 = ((i0 >> 20) & 0x7ff) - 0x3ff; /* exponent of x */
  if (j0 < 20) {                     /* integer part in high x */
    if (j0 < 0) {                    /* |x|<1 */
      __HIp(iptr) = i0 & 0x80000000;
      __LOp(iptr) = 0; /* *iptr = +-0 */
      return x;
    } else {
      i = (0x000fffff) >> j0;
      if (((i0 & i) | i1) == 0) { /* x is integral */
        *iptr = x;
        __HI(x) &= 0x80000000;
        __LO(x) = 0; /* return +-0 */
        return x;
      } else {
        __HIp(iptr) = i0 & (~i);
        __LOp(iptr) = 0;
        return x - *iptr;
      }
    }
  } else if (j0 > 51) { /* no fraction part */
    *iptr = x * one;
    __HI(x) &= 0x80000000;
    __LO(x) = 0; /* return +-0 */
    return x;
  } else {                                    /* fraction part in low x */
    i = ((_UINT32)(0xffffffff)) >> (j0 - 20);
    if ((i1 & i) == 0) {                      /* x is integral */
      *iptr = x;
      __HI(x) &= 0x80000000;
      __LO(x) = 0; /* return +-0 */
      return x;
    } else {
      __HIp(iptr) = i0;
      __LOp(iptr) = i1 & (~i);
      return x - *iptr;
    }
  }
}