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  #if defined(LIBM_SCCS) && !defined(lint)
      16  static char rcsid[] = "$NetBSD: $";
      17  #endif
      18  
      19  /*
      20   * long double logbl(x)
      21   * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
      22   * Use ilogb instead.
      23   */
      24  
      25  #include <math.h>
      26  #include <math_private.h>
      27  #include <libm-alias-ldouble.h>
      28  #include <math-use-builtins.h>
      29  
      30  _Float128
      31  __logbl (_Float128 x)
      32  {
      33  #if USE_LOGBL_BUILTIN
      34    return __builtin_logbl (x);
      35  #else
      36    /* Use generic implementation.  */
      37    int64_t lx, hx, ex;
      38  
      39    GET_LDOUBLE_WORDS64 (hx, lx, x);
      40    hx &= 0x7fffffffffffffffLL;	/* high |x| */
      41    if ((hx | lx) == 0)
      42      return -1.0 / fabsl (x);
      43    if (hx >= 0x7fff000000000000LL)
      44      return x * x;
      45    if ((ex = hx >> 48) == 0)	/* IEEE 754 logb */
      46      {
      47        /* POSIX specifies that denormal number is treated as
      48           though it were normalized.  */
      49        int ma;
      50        if (hx == 0)
      51  	ma = __builtin_clzll (lx) + 64;
      52        else
      53  	ma = __builtin_clzll (hx);
      54        ex -= ma - 16;
      55      }
      56    return (_Float128) (ex - 16383);
      57  #endif /* ! USE_LOGBL_BUILTIN  */
      58  }
      59  
      60  libm_alias_ldouble (__logb, logb)