1  /* s_ilogbl.c -- long double version of s_ilogb.c.
       2   */
       3  
       4  /*
       5   * ====================================================
       6   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
       7   *
       8   * Developed at SunPro, a Sun Microsystems, Inc. business.
       9   * Permission to use, copy, modify, and distribute this
      10   * software is freely granted, provided that this notice
      11   * is preserved.
      12   * ====================================================
      13   */
      14  
      15  #if defined(LIBM_SCCS) && !defined(lint)
      16  static char rcsid[] = "$NetBSD: $";
      17  #endif
      18  
      19  /* ilogbl(long double x)
      20   * return the binary exponent of non-zero x
      21   * ilogbl(0) = FP_ILOGB0
      22   * ilogbl(NaN) = FP_ILOGBNAN (no signal is raised)
      23   * ilogbl(+-Inf) = INT_MAX (no signal is raised)
      24   */
      25  
      26  #include <limits.h>
      27  #include <math.h>
      28  #include <math_private.h>
      29  #include <math_ldbl_opt.h>
      30  
      31  int __ieee754_ilogbl(long double x)
      32  {
      33  	int64_t hx, hxs;
      34  	int ix;
      35  	double xhi, xlo;
      36  
      37  	ldbl_unpack (x, &xhi, &xlo);
      38  	EXTRACT_WORDS64 (hx, xhi);
      39  	hxs = hx;
      40  	hx &= 0x7fffffffffffffffLL;
      41  	if(hx <= 0x0010000000000000LL) {
      42  	    if(hx==0)
      43  		return FP_ILOGB0;	/* ilogbl(0) = FP_ILOGB0 */
      44  	    else			/* subnormal x */
      45  		for (ix = -1022, hx<<=11; hx>0; hx<<=1) ix -=1;
      46  	    return ix;
      47  	}
      48  	else if (hx < 0x7ff0000000000000LL)
      49  	  {
      50  	    int hexp = (hx >> 52) - 0x3ff;
      51  	    /* If the high part is a power of 2, and the low part is
      52  	       nonzero with the opposite sign, the low part affects
      53  	       the exponent.  */
      54  	    if ((hx & 0x000fffffffffffffLL) == 0)
      55  	      {
      56  		int64_t lx;
      57  		EXTRACT_WORDS64 (lx, xlo);
      58  		if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
      59  		  hexp--;
      60  	      }
      61  	    return hexp;
      62  	  }
      63  	else if (FP_ILOGBNAN != INT_MAX) {
      64  	    /* ISO C99 requires ilogbl(+-Inf) == INT_MAX.  */
      65  	    if (hx==0x7ff0000000000000LL)
      66  		return INT_MAX;
      67  	}
      68  	return FP_ILOGBNAN;
      69  }