1  /* s_logbl.c -- long double version of s_logb.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  /*
      16   * long double logbl(x)
      17   * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
      18   * Use ilogb instead.
      19   */
      20  
      21  #include <math.h>
      22  #include <math_private.h>
      23  #include <math_ldbl_opt.h>
      24  #include <fix-int-fp-convert-zero.h>
      25  
      26  long double
      27  __logbl (long double x)
      28  {
      29    int64_t hx, hxs, rhx;
      30    double xhi, xlo;
      31  
      32    ldbl_unpack (x, &xhi, &xlo);
      33    EXTRACT_WORDS64 (hx, xhi);
      34    hxs = hx;
      35    hx &= 0x7fffffffffffffffLL;	/* high |x| */
      36    if (hx == 0)
      37      return -1.0 / fabs (x);
      38    if (hx >= 0x7ff0000000000000LL)
      39      return x * x;
      40    if (__glibc_unlikely ((rhx = hx >> 52) == 0))
      41      {
      42        /* POSIX specifies that denormal number is treated as
      43           though it were normalized.  */
      44        rhx -= __builtin_clzll (hx) - 12;
      45      }
      46    else if ((hx & 0x000fffffffffffffLL) == 0)
      47      {
      48        /* If the high part is a power of 2, and the low part is nonzero
      49  	 with the opposite sign, the low part affects the
      50  	 exponent.  */
      51        int64_t lx;
      52        EXTRACT_WORDS64 (lx, xlo);
      53        if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
      54  	rhx--;
      55      }
      56    if (FIX_INT_FP_CONVERT_ZERO && rhx == 1023)
      57      return 0.0L;
      58    return (long double) (rhx - 1023);
      59  }
      60  #ifndef __logbl
      61  long_double_symbol (libm, __logbl, logbl);
      62  #endif